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We present a successful treatment, with tigecycline monotherapy, of acute prostatitis caused by multidrug-resistant Escherichia coli harboring an NDM-1 carbapemenase along with a CMY-2 cephalosporinase and a TEM ESBL.

Background Enterococcus faecalis have been regarded as one of the leading causes of the nosocomial infections worldwide. Tigecycline (TGC) is considered as a choice of last resort for the treatment of infections caused by multidrug-resistant E. faecalis, however, the emergence of TGC non-susceptibility has posted the therapeutic challenge. Non-susceptibility in clinical strains could be due to resistance (MIC >0.5 mg/l) or heteroresistance. Therefore, this study aimed to understand the underlying molecular mechanisms of TGC resistance and heteroresistance in E. faecalis. Methods In vitro induction experiments were carried out under TGC pressure with two TGC- sensitive E. faecalis strains. Heteroresistance was evaluated by population analysis profiling (PAP) in 270 clinical TGC- sensitive E. faecalis strains. TGC susceptibility was determined by the agar dilution method. Resistance and heteroresistance mechanisms were investigated by identifying genetic mutations in tetracycline (Tet) target sites and susceptibility testing in the presence of the efflux protein inhibitors phenylalanine-arginine-β-naphthylamide (PaβN) and carbonyl cyanide m chlorophenylhydrazine (CCCP). Comparison of single nucleotide polymorphism in the whole genome between the parental isolate and two TGC-resistant strains were investigated by next-generation sequencing. Results No mutations in Tet target sites in seven TGC heteroresistant strains were present, whereas the mutations in Tet target sites of seven TGC-resistant E. faecalis were frequently found (Table 1). TGC MICs in heteroresistant strains were reduced by CCCP (Table 2). Whole genome sequencing revealed the same non-synonymous mutations and transcoding deletions in the exons of several genes encoding for various enzymes or transfer systems (Table 3). Table 1. The characteristics of the antimicrobial susceptibility, resistance mechanism of TGC-induced resistant isolates Table 2. Characteristics of clinical heteroresistant mother E. faecalis strains and heteroresistance-derived E. faecalis clones Table 3. List of mutation-related genes, amino acids and proteins by comparison of whole genome between the parental isolate and the TGC-induced resistant strains Conclusion Our data indicated that the main mechanism of TGC heteroresistance in E. faecalis might be associated with the efflux pumps. TGC resistance in E. faecalis was associated with mutations in the 16SrRNA site or 30S ribosome protein S10. The genetic mutations in several enzymes and transfer systems might also participate in the resistance development to TGC in E. faecalis. Disclosures All Authors: No reported disclosures

Background Ceftazidime-avibactam (CAZ-AVI) is a β-lactam/non-β-lactam β-lactamase inhibitor combination that can inhibit class A, C and some class D β-lactamases. Resistance caused by these β-lactamases often results in multidrug-resistance (MDR). This study evaluated the in vitro activity of CAZ-AVI and comparators against MDR Enterobacterales and Pseudomonas aeruginosa isolates collected from patients in Latin America. Methods Non-duplicate clinical isolates were collected in 2017-2018 in 10 countries in Latin America. Susceptibility testing was performed using CLSI broth microdilution and interpreted using CLSI 2020 and FDA (tigecycline) breakpoints. MDR was defined as resistant (R) to ≥3 of 7 sentinel drugs: amikacin (AMK), aztreonam (ATM), cefepime (FEP), colistin (CST), levofloxacin (LVX), meropenem (MEM), and piperacillin-tazobactam (TZP). Results The activity of CAZ-AVI and comparators against all isolates and MDR subsets is shown in the table. MDR rates for the studied species ranged from 17.6% among E. cloacae to 31.0% among K. pneumoniae. CAZ-AVI was active against 99% of Enterobacterales isolates and maintained activity against 85-99% of MDR isolates of the examined species. Only tigecycline showed comparable or higher activity. Among P. aeruginosa, CAZ-AVI was active against 86% of all isolates and 45% of MDR isolates; no other studied drug was more active. The three most common MDR phenotypes among Enterobacterales were 1) R to ATM, FEP, and LVX (n=538, 50% of all MDR Enterobacterales; 100% susceptible (S) to CAZ-AVI), 2) R to all sentinel drugs except AMK and CST (n=112, 10% of all MDR isolates; 88% S to CAZ-AVI), and 3) R to ATM, FEP, LVX, and TZP (n=111, 10% of all MDR Enterobacterales; 100% S to CAZ-AVI). The three most common MDR phenotypes among P. aeruginosa were 1) R to all sentinel drugs except CST (n=70, 22% of all MDR isolates; 20% S to CAZ-AVI), 2) R to AMK, LVX, and MEM (n=33, 10% of all MDR isolates; 33% S to CAZ-AVI), and 3) R to all sentinel drugs except AMK and CST (n=30, 9% of all MDR isolates; 70% S to CAZ-AVI). Table Conclusion These in vitro data suggest that CAZ-AVI can be an effective treatment option for infections caused by MDR Enterobacterales and P. aeruginosa collected in Latin America. Disclosures Krystyna Kazmierczak, PhD, IHMA (Employee)Pfizer, Inc. (Consultant) Sibylle Lob, PhD, IHMA (Employee)Pfizer, Inc. (Consultant) Greg Stone, PhD, AztraZeneca (Shareholder, Former Employee)Pfizer, Inc. (Employee) Daniel F. Sahm, PhD, IHMA (Employee)Pfizer, Inc. (Consultant)Shionogi & Co., Ltd. (Independent Contractor)

Background Eravacycline (ERV) is a fully-synthetic, fluorocycline antibacterial approved by the FDA and EMA for the treatment of complicated intra-abdominal infections (cIAI) in patients ≥18 years of age. The purpose of this study was to further monitor the in vitro activity of ERV against Gram-positive pathogens, such as Staphylococcus aureus (including methicillin-resistant S. aureus, MRSA), Enterococcus spp. (including vancomycin-resistant Enterococcus, VRE) and Streptococcus spp. Methods Isolates were collected globally during 2018 from various body sites. Minimum inhibitory concentrations (MICs) were determined by CLSI broth microdilution. Antibiotic susceptibility was determined using the most recent CLSI breakpoints (30th ed CLSI M100 document), except for ERV and tigecycline (TGC) where FDA breakpoints from 2018 and 2005, respectively, were applied. Results Summary MIC data for ERV and select comparators are shown in the Table. ERV MIC50/90 for Enterococcus spp were 0.06/0.12 μg/mL and were not affected by the presence of vancomycin resistant mechanisms. The MIC90 of ERV against VRE was 2-fold lower than TGC, at a value of 0.12 μg/mL. ERV MIC90 values for methicillin-susceptible S. aureus (MSSA) was 0.12 μg/mL and for MRSA was 0.25 μg/mL. Generally, for all pathogens, ERV MIC90 values were 2- to 4-fold lower than TGC. Table Conclusion ERV in vitro activity was demonstrated for clinically important Gram-positive pathogens, including resistant isolates. Overall, ERV demonstrated lower MIC90 values than comparators for all organisms. This 2018 global surveillance highlights ERV’s utility against Gram-positive organisms and further underscores its role in cIAI, where these pathogens play a causative role. Disclosures Steven Morgan, PharMD, Tetraphase Pharmaceuticals (Employee) Sara Hwang, PharMD, Tetraphase Pharmaceuticals (Employee) Ekaterina Efimova, PharMD, Tetraphase Pharmaceuticals (Employee) Stephen Hawser, PhD, Tetraphase Pharmaceuticals (Scientific Research Study Investigator) Virgil Lijfrock, PharMD, Tetraphase (Employee)

Background Enterococcus faecium infections are difficult to treat and there is a growing concern regarding the rising occurrence of daptomycin resistance. We have previously demonstrated that only daptomycin plus ampicillin combination was effective against DAP-R E. faecium R497. The efficacy and systematic screening DAP plus β-lactams and DAP plus other combinations against daptomycin-resistant strains of E. faecium has not been investigated. Here, we evaluated 40 selected single, dual and triple combinations of antibacterial regimens against two clinical isolates of DAP-R E. faecium (R497 and R496 (with daptomycin MIC of 16 and 32 µg/ml, respectively). Methods E.faecium R497 and R496 were tested against an array of antibacterial agents including daptomycin, tigecycline, linezolid, ertapenem, ceftaroline and ceftriaxone using MIC susceptibility tests and 24h time-kill curves (TKC). All susceptibility tests and TKCs were performed in MHB broth containing 50 mg/L calcium. TKCs were performed at half MIC or free peak concentration of each antibacterial (whichever was lower). Synergy was defined as >2 log10 CFU/ml decrease compared to the most potent antibacterial agent. Results Susceptibility tests demonstrated resistance to all listed β-lactams for both organisms. TKCs demonstrated that combination of daptomycin-ertapenem, daptomycin-ceftriaxone and daptomycin-ceftaroline was not effective against R497. However, addition of ceftriaxone or linezolid to either daptomycin-ertapenem or daptomycin-ceftaroline combinations resulted in synergy against this organism. Combinations of daptomycin-ertapenem and daptomycin-ceftaroline were synergistic against R496. Addition of linezolid, ceftriaxone or tigecycline to either daptomycin-ceftaroline or daptomycin-ertapenem combination did not increase killing activity against R496. Conclusion Differential affinity of β-lactams to specific PBP isotypes seems to be a key parameter for the success of daptomycin- β-lactam combinations against multi-drug resistant E. faecium . The optimized use of double β-lactam therapy in addition to daptomycin can potentially lead to improved patient outcomes and preserving antibiotic therapy for serious enterococcus infections. Disclosures Cesar A. Arias, MD, MSc, PhD, FIDSA, Entasis Therapeutics (Scientific Research Study Investigator)MeMed (Scientific Research Study Investigator)Merck (Grant/Research Support) Michael J. Rybak, PharmD, MPH, PhD, Paratek (Grant/Research Support)

Background Vancomycin-resistant Enterococci (VRE) are nosocomial pathogens that cause significant morbidity and mortality especially among patients with chronic medical conditions, critical illness and prolonged hospitalizations. Majority of human infections are caused by two species— E. faecium and E. faecalis, and which can acquire resistance to ampicillin, aminoglycosides, and vancomycin. Our aim was to study the susceptibility profile of the VRE strains to the tetracycline group of antibiotics on isolates collected from our local hospital. Older tetracyclines and their novel derivatives are included in this study. Methods Eighty preserved isolates of VRE were tested against five tetracyclines, i.e. doxycycline, minocycline, tigecycline, eravacycline and omadacycline. Antimicrobial susceptibility testing was performed using the E-test method in accordance to CLSI guidelines. Isolates were then classified as either susceptible, intermediately susceptible or resistant based on established breakpoints. Results Eighty isolates (54 VRE. faecium and 26 VRE. faecalis) were included in the study. Out of 54 E. faecium isolates, 52 (96.3%) were susceptible to tigecycline, 15 (27.8%) were susceptible to minocycline, 14 (25.9%) were susceptible to doxycycline, 42 (77.8 %) were susceptible to omadacycline, and 52 (96.3%) were susceptible to eravacycline. Out of 26 E. faecalis isolates, 26 (100%) were susceptible to tigecycline, 2 (7.6%) were susceptible to minocycline, 2 (7.6%) were susceptible to doxycycline, 2 (7.6%) were susceptible to omadacycline, and 25 (96.15%) were susceptible to eravacycline. Conclusion Tigecycline and eravacycline exhibited better in vitro antimicrobial activity against vancomycin-resistant E. faecium and E. faecalis when compared to doxycycline and minocycline. Omadacycline showed a relatively favorable susceptibility profile for E. faecium, but less favorable for E. faecalis. Results of this study will be useful to incorporate in the local antibiogram and will guide antimicrobial stewardship efforts. These findings will not only add to existing knowledge on susceptibility profiles of the novel tetracyclines, i.e. eravacycline and omadacycline, but also on their applicability in the clinical setting. Disclosures All Authors: No reported disclosures

Background Ceftazidime-avibactam (CAZ-AVI) is a β-lactam/non-β-lactam β-lactamase inhibitor combination with activity against Enterobacterales producing class A, C and some class D β-lactamases. Resistance caused by these β-lactamases is especially high in ICUs. This study evaluated the in vitro activity of CAZ-AVI and comparators against Enterobacterales isolates from patients in ICU and non-ICU wards. Methods Non-duplicate clinical isolates were collected in 2017-2018 from patients in Asia/Pacific, Europe, Latin America, and Middle East/Africa. Susceptibility testing was performed using CLSI broth microdilution and interpreted using CLSI 2020 and FDA (tigecycline) breakpoints. PCR and sequencing were used to determine the β-lactamase genes present in all isolates with meropenem (MEM) MIC >1 µg/ml, and Escherichia coli, Klebsiella spp. and Proteus mirabilis with aztreonam or ceftazidime MIC >1 µg/ml. Results The activity of CAZ-AVI and comparators is shown in the table. Susceptibility rates among global Enterobacterales were generally lower for isolates from patients in ICU than non-ICU wards, but this difference was small for CAZ-AVI, which inhibited ≥97% of isolates from both ward types. Among MEM-nonsusceptible (NS) isolates, CAZ-AVI was active against 66.5% and 68.1% of ICU and non-ICU isolates, respectively (of which 31.8% and 30.8%, respectively, carried metallo-β-lactamases [MBLs]). CAZ-AVI inhibited >97% of MEM-NS MBL-negative isolates collected globally. Antimicrobial activity against all Enterobacterales from both ICU and non-ICU wards in Latin America (LA) was generally similar to the global average. Among MEM-NS isolates, antimicrobial activity of CAZ-AVI and TGC was higher in LA than the global average among isolates from both ward types, at least partly because of a lower proportion of MBL-positive isolates in this subset (15.8% and 17.9% in ICU and non-ICUs, respectively). CAZ-AVI inhibited 100% of MEM-NS MBL-negative isolates from LA. Table Conclusion CAZ-AVI provides a valuable treatment option for infections caused by Enterobacterales that do not carry MBLs, including those among patients in ICU wards, where antimicrobial resistance is typically higher. Disclosures Sibylle Lob, PhD, IHMA (Employee)Pfizer, Inc. (Consultant) Krystyna Kazmierczak, PhD, IHMA (Employee)Pfizer, Inc. (Consultant) Greg Stone, PhD, AztraZeneca (Shareholder, Former Employee)Pfizer, Inc. (Employee) Daniel F. Sahm, PhD, IHMA (Employee)Pfizer, Inc. (Consultant)Shionogi & Co., Ltd. (Independent Contractor)

Antibiotic resistance is an ongoing global medical crisis and we are in great need of new antibacterial agents to combat rapidly emerging resistant pathogens. Tigecycline is one of few drugs that have been introduced into medicine during the last two decades. It is a broad-spectrum third generation tetracycline that is active against multidrug-resistant bacteria that cause complicated infections.In this thesis I examined the development of tigecycline resistance in Escherichia coli and associated in vitro and in vivo fitness effects. Selections of spontaneous E. coli mutants revealed relatively high accumulation rates of changes in the multidrug efflux system AcrAB-TolC regulation network and in heptose biosynthesis and transport pathways important for lipopolysaccharide (LPS) synthesis. Both groups of mutations led to reduced susceptibility to tigecycline and slower growth compared to the wild-type bacteria. Additional in vitro fitness assays and in vivo competitions showed that LPS mutants were less fit than efflux mutants, providing a possible explanation for why up-regulation of multidrug efflux pumps is the main tigecycline resistance mechanism reported in clinical isolates.Tigecycline was designed to evade the two most common tetracycline resistance mechanisms conferred by Tet proteins, efflux and ribosomal protection. However, tigecycline is a substrate for the tetracycline modifying enzyme Tet(X). Screening of Tet protein mutant libraries showed that it is possible to select Tet mutants with minimal inhibitory concentrations of tigecycline that reach clinically relevant levels. Mutations in Tet proteins that permitted a better protection from tigecycline frequently exhibited reduced activity against earlier generations of tetracyclines, except for the Tet(X) enzyme mutants, which were better at inactivating all tested tetracyclines. This is particularly worrisome because different variants of Tet(X) have recently spread to multidrug-resistant pathogens through horizontal gene transfer. Therefore, Tet(X) mutants with improved activity threaten the medical future of tetracyclines.Multidrug resistance is easily disseminated through horizontally spreading conjugative plasmids. pUUH239.2 is an example of a successful conjugative plasmid that caused the first clonal outbreak of extended spectrum β-lactamase-producing Klebsiella pneumoniae in Scandinavia. This plasmid was formed after rearrangements between two different plasmid backbones and it carries resistance genes to multiple antibiotic classes, heavy metals, and detergents.

Background Carbapenemases are the most frequent mechanism of carbapenem resistance in Enterobacteriaceae. However, alternative mechanisms such as loss of porin channels or up-regulation of efflux pumps can cause intermediate- to high-level resistance to ertapenem (ERTA) and possibly reduced susceptibilities to meropenem (MERO) leading to discordant phenotypic profiles. Clinical implications of discordant carbapenem susceptibilities and optimal therapy options are yet unknown. We sought to describe our experience with carbapenem-discordant Enterobacteriaceae (CDE). Methods Descriptive study of hospitalized adult patients with a CDE positive culture from December 1/16 - December 1/18. Discordance was defined as Enterobacteriaceae with an ERTA-resistant and MERO-susceptible phenotype. Primary objective was to describe antibiotic use patterns for CDE infections. Secondary outcomes included infectious diseases (ID) involvement and clinical outcomes. Clinical failure was defined as a composite of in-hospital mortality, switch of definitive therapy due to clinical worsening, re-hospitalization within 30 days for re-infection, or failure to achieve blood culture clearance for ≥7 days. Results A total of 55 patients with CDE were identified. Most common organisms were Enterobacter cloacae complex (72%) and Klebsiella pneumoniae (9%). Of 21 isolates tested, 1 (4.8%) was positive for a carbapenemase. Mean age of patients was 61 ± 16 years, 51% were admitted to a medicine service, and 18% were immunocompromised. ID was involved in 82% of CDE cases. Most common sites were urine (33%), wound/tissue (27%), and respiratory (18%). 43/55 (78%) patients were treated – 17/43 (40%) with MERO, 14/43 (33%) with fluoroquinolones. Ceftazidime/avibactam and tigecycline were used in 4 (9%) patients each. Combination therapy was used in 8 (19%) patients, most commonly with MERO or tigecycline. Clinical failure occurred in 21/43 (49%) patients – 8/43 (19%) were receiving MERO-based therapy, 13/43 (30%) were receiving a non-MERO-based therapy. Conclusion Discordance between ERTA and MERO susceptibility was more common in Enterobacter spp. Majority of isolates tested negative for a carbapenemase. MERO and fluoroquinolones were the most frequently used antibiotics for treatment of CDE infections. Disclosures All authors: No reported disclosures.

Background CREs are feared pathogens with resistance occurring through the production of carbapenemases. Identification of carbapenemase-producing (CP) organisms assists with proper antimicrobial selection of commonly used agents, such as ceftazidime/avibactam (CA), meropenem/vaborbactam (MV), and tigecycline (TG). AdventHealth Orlando implemented a CRE screening method based on meropenem (MER) and a confirmatory CRE PCR testing in March 2018. Prior to implementing this test, patients were deemed to have CRE infections (CREI) if the organism demonstrated resistance to any carbapenem. The objective of this study was to evaluate the impact of this testing on the utilization of anti-CRE antibiotics. Methods This was a retrospective pre (March 2017–February 2018)- and post (March 2018–February 2019)-implementation study examining the impact of CRE PCR testing. Outcomes included the number of antibiotic days saved, average duration of therapy (DOT), median length of stay (LOS), and change in CP-CRE prevalence. The intervention consisted of the implementation of CRE PCR testing and included inpatients > 18 years old who received either CA, MV, or TG for the treatment of a CREI. Results Post-implementation, 30 unique patients were identified as having a positive K. pneumoniae carbapenemase gene by PCR, indicating a CP-CRE and received CA, MV, or TG; whereas, 42 patients in the pre-implementation group had a CREI and received CA, MV, or TG. Testing to identify CP-CREs led to a 50% reduction in the number of antibiotic days for CA, MV, and TG (575 vs. 287 days, P < 0.0001). Additionally, the average DOT decreased by 2.5 days in the post-implementation group (10.5 days vs. 8 days, P = 0.18) along with a 3.5-day shorter median LOS (15 days vs. 11.5 days, P = 0.48). The CRE prevalence based on resistance only to MER is 0.27%, compared with the previously reported rate of 2.5% that included resistance to ertapenem or MER. Conclusion Implementing CRE PCR testing to identify CP-CRE organisms resulted in a significant reduction in utilization of anti-CRE agents for CREIs. Additionally, the testing algorithm allowed for accurate reporting of our local CRE prevalence. By avoiding CA, MV, or TG in patients without CP-CREs, this has the potential to optimize therapy while reducing collateral damage associated with broad-spectrum agents. Disclosures All authors: No reported disclosures.

Background Colistin is a last resort antibiotic against infections with CRKp. Its increased use has led to resistance to this antibiotic. Methods This was a single-center, retrospective, cohort study including all CRKp BSIs treated between January 1, 2014 and July 31, 2018. Antibiotic therapy was appropriate if initiated within 5 days from the onset of BSI including at least an active drug with an adequate dosage. Exclusion criteria were missing key data, death < 24 h after inclusion, subsequent episodes in the same patients, pregnancy, polymicrobial BSI, < 18 years of age, no ID consultation, no carbapenemase gene detection by multiplex PCR for blaKPC, blaNDM, blaVIM, blaIMPand blaOXA48. EUCAST breakpoints were used for antibiotic susceptibilities. Colistin MIC was determined by using broth microdilution. FDA criteria were applied for tigecycline susceptibility Results Among 174 CRKp BSIs, 129 met all inclusion criteria. Susceptibility to antibiotics was as follows: colistin (51.9%), tigecycline (67.4%), gentamicine (38.0%), amikacin (43.0%), meropenem (32.6%), ciprofloxacin (18.6%), TMP-SMX (24.0%), ceftazidime (7.8%), cefepime (7.8%). 66.1% and 19.4% of the patients received inappropriate therapy in ColR-CRKp and ColS-CRKp groups, respectively (P ≤ 0.001). We incorporated interaction between colistin susceptibility and inappropriate therapy into multivariate logistic regression analysis (MLRA) that was constructed for identification of independent risk factors for 30-day mortality. The variables having P ≤ 0.1 in crude analysis were included in MLRA. After checking correlation between variables by Pearson correlation analysis and multicollinearity analysis, the final model was builded. The results are shown in Table 2. Conclusion Colistin resistance and inappropriate therapy were not associated with decreased mortality individually, however their interaction significantly increased 30-day mortality rate (OR: 4.04; 95% CI: 1.62–10.02; P = 0.003).85.5% of ColR-CRKp isolates produced an OXA-48 enzyme which can be inhibited by ceftazidime–avibactam, but not available in our setting, treatment with this agent may have altered the mortality rates. Thus, high rate colistin resistance among CRKp isolates remains as a significant cause of mortality in our setting. Disclosures All authors: No reported disclosures.

Background Carbapenem-resistant Acinetobacter baumannii (CRAB) infection is an emerging clinical issue and shows high mortality rates. There are a few studies that have evaluated the microbiologic risk factors for mortality in CRAB bacteremia. Aim of this study is to identify the clinical and microbiologic risk factors for mortality in CRAB bacteremia. Methods Adult patients with monomicrobial CRAB bacteremia at a 2,700-bed tertiary hospital between December 2012 and December 2018 were retrospectively enrolled in the study. Risk factors for 30-day mortality were evaluated through a detailed clinical and microbiological analysis of study patients. All isolates collected on the first day of bacteremia were subjected to colistin susceptibility testing by broth microdilution and genotyping by multilocus sequence typing (MLST). Results A total of 164 patients were enrolled and 90 (55%) died within 30 days. Of the 164 patients, 111 (68%) were male and median age was 66.5 years. The most common MLST genotype was ST191 (80 isolates, 49%), followed by ST451 (14%) and ST784 (13%), and 12 (7%) isolates were resistant to colistin (MIC ≥4 mg/L). Deceased patients were more likely to have hematologic malignancy, neutropenia, pneumonia, and primary bacteremia; less likely to have solid tumor, catheter-related infection, and biliary tract infection; more likely to have a high Pitt bacteremia score; and less likely to receive appropriate antibiotic treatment, colistin, and combination therapy with colistin and tigecycline, compared with surviving patients (Table 1). Genotype, colistin MIC, and colistin resistance were not associated with mortality (Figure 1 and 2). In multivariable analysis, neutropenia (aOR, 3.25; 95% CI, 1.18–8.95), catheter-related infection (aOR, 0.33; 95% CI, 0.11–0.99), biliary tract infection (aOR, 0.20; 95% CI, 0.04–0.99), a high Pitt bacteremia score (aOR,1.42; 95% CI, 1.20–1.67), and combination therapy with colistin and tigecycline (aOR, 0.36; 95% CI, 0.14–0.92) were independent risk factors for mortality (Table 2). Conclusion Clinical factors such as the site of infection, severity of bacteremia, and specific combination therapy rather than microbiologic factors contributed to mortality in CRAB bacteremia. Appropriate combination therapy may help improving outcomes in CRAB bacteremia. Disclosures All authors: No reported disclosures.

Background The recent discovery of carbapenemase-producing hypervirulent Klebsiella pneumoniae (CP-HvKP) has signaled the convergence of multidrug resistance and pathogenicity, with the potential for increased mortality. While previous studies of CP-HvKP isolates revealed that most carried carbapenemase genes and hypervirulence elements on separate plasmids, a 2018 report from China confirmed that both could be harbored on a single, hybrid carbapenemase-hypervirulent plasmid. As part of a project sequencing isolates carrying multiple carbapenemase genes identified through CDC’s Antibiotic Resistance Laboratory Network (AR Lab Network), we discovered a blaNDM-1-bearing hypervirulent plasmid found in a KPC- and NDM-positive K. pneumoniae from the United States. Methods Antimicrobial susceptibility testing (AST) was performed by reference broth microdilution against 23 agents. Whole-genome sequencing (WGS) was performed on Illumina MiSeq and PacBio RS II platforms. Results AST results indicated the isolate was extensively drug-resistant, as it was non-susceptible to at least one agent in all but two drug classes; it was susceptible to only tigecycline and tetracycline. Analysis of WGS data showed the isolate was ST11, the same sequence type that caused a fatal outbreak of CP-HvKP in China in 2016. The genome included two plasmids. The smaller one (129kbp) carried seven antibiotic resistance (AR) genes, including the carbapenemase gene blaKPC-2. The larger plasmid (354kbp) harbored 11 AR genes, including the metallo-β-lactamase gene blaNDM-1, as well as virulence factors iucABCD/iutA, peg-344, rmpA, and rmpA2, which comprise four of the five genes previously identified as predictors of hypervirulence in K. pneumoniae. Conclusion This is the first report of a hybrid carbapenemase-hypervirulent plasmid in the United States. The presence of both blaNDM-1 and hypervirulence elements on the same plasmid suggests that the CP-Hv pathotype could spread rapidly through horizontal transfer. This discovery demonstrates the critical role of genomic characterization of emerging resistance and virulence phenotypes by the AR Lab Network as part of US containment efforts. Disclosures All authors: No reported disclosures.

Background Eravacycline (ERV) is a recently-approved, fully synthetic fluorocycline agent that demonstrates broad in vitro activity against multidrug-resistant pathogens. We sought to compare the activity of ERV with minocycline (MIN) and tigecycline (TGC) against diverse CRE clinical isolates, and to evaluate the performance of commercially-available susceptibility testing methods. Methods ERV, MIN, and TGC minimum inhibitory concentrations (MICs) were determined in triplicate by broth microdilution against previously characterized CRE isolates. ERV susceptibility was also measured by disk diffusion (20 µg disk; Mast Group) and MIC test strips (MTS; Liofilchem) according to manufacturer instructions. Results 148 CRE were tested, including 92 K. pneumoniae, 32 Enterobacter spp, 11 E. coli, 5 C. freundii, 4 K. oxytoca, and 4 S. marcescens. 72% of isolates harbored blaKPC, which encoded KPC-2 (n = 33), KPC-3 (n = 48), and other KPC variants (n = 22). 77% and 19% of isolates were resistant to meropenem and ceftazidime–avibactam, respectively. By BMD, the ERV, MIN, and TGC MIC range, MIC50 and MIC90 for shown in the Table. ERV MICs were ≥2-fold lower than MIN and TGC against 99% and 43% of isolates, respectively. ERV MICs did not vary by species or KPC-subtype. ERV MICs determined by BMD and MTS were well-correlated showing 89% essential agreement (MIC within one 2-fold dilution; Figure). The rate of categorical agreement (CA) was 73%. By comparison, the CA rate between BMD and disk diffusion was 78%. By both MTS and disk diffusion methods, susceptibility results clustered on either side of the susceptibility breakpoint. 50% of disk diffusion zones clustered between 14 and 16 millimeters (mm), which is 1 mm on either side of the susceptibility breakpoint (≥15 mm). Conclusion This study confirms the in vitro activity of ERV against CRE clinical isolates, which is comparable to TGC. ERV MTS demonstrated high rates of EA, but lower rates of CA. Clinicians should be aware of the nuances of ERV susceptibility testing and recognize that the modal distribution of ERV MICs against CRE lies on either side of the susceptibility breakpoint. Disclosures All authors: No reported disclosures.

We characterized use of the carbapenems, polymyxins, and tigecycline in United States children’s hospitals between 2010 and 2014. We found substantial variability in use across hospitals and overall decreased use over time. Most polymyxin and tigecycline use occurred in cystic fibrosis patients, and appendectomy was a common indication for carbapenem therapy.

Background Antibiotic-resistant Gram-negative bacteria, including KPC-producing Enterobacteriaceae and carbapenem-resistant A. baumannii, have been problematic hospital pathogens in NYC and other areas. Eravacycline (ERV), a fluorocycline antibiotic released in the USA in 2018, has demonstrated in vitro activity against many of these strains. We tested the activity of ERV against a recent collection of clinical isolates from NYC hospitals. Methods For a 3-month period in 2017, all unique patient isolates of E. coli, K. pneumoniae, Enterobacter spp., and A. baumannii were collected from 7 hospitals in Brooklyn, NY. MICs were performed by broth microdilution for ERV and Tigecycline (TGC) and agar dilution for other antibiotics according to CLSI methodology. Cephalosporin-resistant isolates were screened by PCR for common carbapenemases. Results The susceptibility results for tetracycline and ERV are listed in the Table. Overall, 95% of the Enterobacteriaceae were inhibited by ≤ 0.5 μg/mL of ERV, the FDA-suggested breakpoint. Of 1,876 isolates of E. coli, 4 possessed KPC. ERV MICs for these 4 isolates were 0.125–0.25 μg/mL. Of 518 isolates of K. pneumoniae, 20 possessed KPC. The ERV MIC50 and MIC90 for these isolates were 1 and 1 μg/mL, respectively. Of 172 isolates of Enterobacter spp., 3 possessed KPC. ERV MICs for these 3 isolates were 0.5–1 μg/mL. Of 45 isolates of A. baumannii, 11 isolates possessed a carbapenemase (OXA23 in 8, OXA24 in 2, and KPC in 1). The ERV MIC50 and MIC90 for these isolates were 1 and 2 μg/mL, respectively. Overall, ERV MICs were two-fold lower than TGC MICs for A. baumannii. Conclusion ERV possesses significant in vitro activity against contemporary clinical isolates of Enterobacteriaceae and A. baumannii from NYC, including many carbapenemase producing strains. Disclosures All authors: No reported disclosures.

Background M/V demonstrates potent in vitro activity against KPC-producing organisms. It is unclear whether the combination interacts synergistically with other active agents. Methods We tested isolates for responses to M/V alone (1 and 4x MIC; V fixed at 8 µg/mL), and in combination with colistin (COL; 2 µg/mL), fosfomycin (FOS; 100 µg/mL + 25 µg/mL G6P), gentamicin (GEN; 2 µg/mL), and tigecycline (TGC; 2 µg/mL) by time-kill using a starting inoculum of 1 × 108 cFu/mL. 24h was the primary endpoint. Results 16 KPC-Kp isolates were studied (7 KPC-2 and 9 KPC-3); all were M/V-susceptible (MIC range: 0.015 – 4 µg/mL). 44% harbored ompK36 mutations (4 IS5 promoter insertion, 2 134–135 DG duplication, and 1 premature stop codon). Median M/V MICs were higher against isolates with mutant ompK36 (0.25 vs. 0.03; P = 0.002). Mean log-kills by M/V at 1x and 4x were -0.50 and -2.41, respectively; M/V was bactericidal (≥3-log kill) against 6% and 56%, respectively (Figure 1). Mean log-kills at 4× were greater against KPC-2 (-3.79) than KPC-3 (−1.33) isolates (P = 0.09), and among isolates with (−3.31) vs. without (−1.71) ompK36 mutations (P = 0.11). GEN was the most active single agent (bactericidal against 56%, mean log-kill = −3.04). In combo with M/V, rates of synergy (>2-log kill in combo) with COL, FOS, GEN, and TGC were 44%, 19%, 12.5%, and 12.5%, respectively (Figure 2). Corresponding rates of bactericidal activity were 44%, 25%, 69%, and 31%, respectively. Antagonism (> 1-log kill by most active single agent) was identified for each combo against 2 isolates. Mean log-kills by M/V + GEN were greater against isolates with GEN MICs ≤1 (−7.16) vs. ≥2 (−1.66; P = 0.001), reflecting the activity of GEN alone. Mean log-kills by M/V + COL were greater against isolates with IS5 insertions (-6.32) compared with wild type (−2.38) or other mutations (−1.77) in ompK36. Responses to M/V + FOS were not dependent upon FOS MIC, but log-kills were greater against mutant (-2.13) vs. wild-type (0.01) ompK36 (P = 0.03). Conclusion M/V + GEN is rapidly cidal if GEN MICs are ≤1, while M/V + COL resulted in highest rates of synergy against diverse KPC-Kp. Mean log-kills were highest among isolates with IS5 promoter insertions suggesting a potential role for COL combination therapy against KPC-Kp isolates with decreased outer membrane permeability. Disclosures All authors: No reported disclosures.

Objectives To assess the Gram-positive-specific antibiotic linezolid and the broad-spectrum antibiotic tigecycline for use in local antibiotic delivery via antibiotic-loaded bone cement. \ud \ud \ud Methods Linezolid and tigecycline were added to Biomet bone cement at varying concentrations. Antibiotic elution over 1 week was quantified by HPLC-MS. The effect of wear on elution over 51 h was determined using a modified TE-66 wear tester. Eluted antibiotics were used to determine the MICs for a panel of clinically relevant bacteria. The impact strength of antibiotic-loaded samples was determined using a Charpy-type impact testing apparatus. Cytotoxicity of eluted antibiotics against MG-63 cells was evaluated using an MTT assay. \ud \ud \ud Results Linezolid and tigecycline eluted from bone cement to clinically relevant levels within 1 h and retained activity over 1 week. Mechanical wear significantly reduced elution of tigecycline, but had little effect on elution of linezolid. Linezolid showed low cytotoxicity towards MG-63 cells with ≤300 mg/mL resulting in >50% cell activity. Cytotoxicity of tigecycline was higher, with an IC50 of 5–10 mg/L. \ud \ud \ud Conclusions Linezolid and tigecycline retain activity after elution from bone cement. The concentration of tigecycline may need to be carefully controlled due to cytotoxicity. The effect of wear on bone cement may need to be considered if tigecycline is to be used for local delivery. Up to 10% linezolid can be added without affecting the impact strength of the bone cement. These results are promising indications for future investigation of these antibiotics for use in local antibiotic delivery strategies.

Background Obesity is on course to overtake being underweight as a global disease burden. Obesity alters antibacterial pharmacokinetics (PK) and pharmacodynamics (PD). Historically, drug PK/PD parameters have not been studied in obese populations. This means dose recommendations risk being sub-therapeutic in a population at increased risk of infection. Suboptimal antibacterial prescribing is widely associated with treatment failure, worse clinical outcomes, unnecessary escalation to broad-spectrum therapy and the emergence of antimicrobial resistance (AMR). Objectives To analyse current information provided by pharmaceutical companies, for the most commonly prescribed antibacterial agents in the UK, for evidence of dosing guidance for obese adults. Methods We analysed the manufacturers' Summary of Product Characteristics (SPC) for 42 of the most clinically important and frequently prescribed antibacterial agents dispensed across both primary and secondary care. The manufacturer's SPC was reviewed, and cross-referenced with the online British National Formulary, to assess dosing guidance for obese adults. Results No advice was provided to guide dosing for obese adults in 35 (83%) of 42 of the most clinically important and frequently prescribed antibacterial agents in the UK. Seven (17%) antibacterial agents (tigecycline, vancomycin, daptomycin, amikacin, gentamicin, tobramycin and teicoplanin) provided variable levels of advice. Conclusions There is a paucity of advice and evidence in the UK to guide dosing common antibacterial agents in the obese. The literature on antibacterial PK/PD studies in obese populations remains scarce. In the face of the increasing risks of AMR combined with the global rise of obesity there is an urgent need to address this significant research gap.

Metallo-β-lactamase-producing Enterobacteriaceae are emerging in the U.S. and are becoming a significant threat. Unfortunately, there is little recognition of the increasing reports of these organisms in U.S. children, a vulnerable population that may suffer severe long-term consequences., Metallo-β-lactamases (MBLs) are emerging as the most notable resistance determinants in Enterobacteriaceae. In many cases, the genes encoding MBLs are part of complex, mobile genetic elements that carry other resistance determinants. In the United States, there are increasing reports of MBL-producing Enterobacteriaceae, with New Delhi MBLs (NDMs) accounting for the majority of transmissible MBL infections. Many infections caused by NDM-producing bacteria are associated with international travel and medical tourism. However, little recognition of the introduction of MBL-producing Enterobacteriaceae into the pediatric community has followed. Reports suggest that this occurred as early as 2002. Here, we reflect on the unwelcome emergence of MBL-producing Enterobacteriaceae in US children and the available clinical and molecular data associated with spread. Since 2002, there have been disturbing reports that include the most readily transmissible MBLs, blaIMP, blaVIM, and blaNDM types. In the majority of children with available data, a history of foreign travel is absent.

Standard treatment for severe Clostridium difficile infection (CDI) is oral vancomycin with metronidazole. After failure of this standard regimen, treatment becomes challenging. A young woman treated for septic shock developed CDI. Standard treatment failed and she was ineligible for fecal transplant. Addition of tigecycline to her regimen resulted in cure.

Recent reports of reduced response to standard therapies for Clostridium difficile infection (CDI) and the risk for recurrent CDI that is common with all currently available treatment agents have posed a significant challenge to clinicians. Current recommendations include metronidazole for treatment of mild to moderate CDI and vancomycin for severe CDI. Results from small clinical trials suggest that nitazoxanide and teicoplanin may be alternative options to standard therapies, whereas rifaximin has demonstrated success in uncontrolled trials for the management of multiple recurrences. Anecdotal reports have also suggested that tigecycline might be useful as an adjunctive agent for the treatment of severe complicated CDI. Reports of resistance will likely limit the clinical use of fusidic acid and bacitracin and, possibly, rifaximin if resistance to this agent becomes widespread. Treatment of patients with multiple CDI recurrences and those with severe complicated CDI is based on limited clinical evidence, and new treatments or strategies are needed.

Background Delafloxacin (DLX) is an investigational anionic fluoroquinolone with an NDA that is under US FDA review to treat acute bacterial skin and skin structure infections and is undergoing Phase 3 studies to treat community-acquired bacterial pneumonia. Methods A total of 36,683 Gram-positive (GP) and -negative (GN) bacteria isolated during 2014–2016 were selected from medical centers in the US and Europe. Susceptibility testing (S) was performed by frozen-form broth microdilution methods for DLX and comparators. Results DLX was very active against Staphylococcus aureus (SA, n = 9,355; MIC50/90, 0.008/0.5 mg/L) while the levofloxacin (LEV) MIC50/90 was 0.25/>4 mg/L (67.9%S). The MIC50/90 for methicillin-resistant SA (MRSA) was 0.12/1 mg/L. For MRSA, all isolates were S to vancomycin and daptomycin (DAP), linezolid and tigecycline (TGC) S was ≥99.9%. Decreased rates of S were noted for LEV (29.8%), clindamycin (72.9%), and erythromycin (17.3/17.8%; CLSI/EUCAST). Minocycline (MIC50/90, 0.12/0.25 mg/L), ceftaroline (MIC50/90, 0.25/0.5 mg/L), DAP (MIC50/90, 0.5/0.5 mg/L), and DLX (MIC50/90, 0.015/0.5 mg/L) were the most active agents tested against coagulase-negative staphylococci. Against Streptococcus pneumoniae (SPN), the MIC50/90 for DLX (0.015/0.03 mg/L) and TGC (0.03/0.06 mg/L) were the lowest among the agents tested. The DLX MIC50/90 values did not vary among the penicillin-S, -intermediate, and -R subgroups of SPN. The MIC50/90 values for DLX against S. pyogenes and S. agalactiae were 0.015/0.03 mg/L. DLX was highly active against Haemophilus influenzae. The DLX MIC50/90 (≤0.001/0.004 mg/L) was the same for β-lactamase positive and negative H. influenzae. Against Enterobacteriaceae, 76.0% of DLX MIC values were ≤1 mg/L. Susceptibility to LEV was 80.8%, and S to ceftriaxone, ceftazidime (CAZ), and cefepime ranged from 78.5–86.3%. A total of 72.6% of Pseudomonas aeruginosa isolates exhibited DLX MIC values ≤1 mg/L, while LEV S was 73.2% and CAZ was 81.6%. The MIC50/90 for both DLX and LEV were 0.5/>4 mg/L, respectively. Conclusion DLX was active against a broad range of GP and GN bacteria, including MRSA and multidrug-resistant SPN. DLX merits further study as therapy in infections in which these organisms may occur. Disclosures R. K. Flamm, Melinta Therapeutics: Research Contractor, Research grant D. Shortridge, Melinta Therapeutics: Research Contractor, Research grant M. D. Huband, Melinta Therapeutics: Research Contractor, Research grant S. McCurdy, Melinta Therapeutics: Employee, Salary M. A. Pfaller, Melinta Therapeutics: Research Contractor, Research grant

Background Carbapenemase producing Enterobacteriaceae (CPE) is major pathogens in nosocomial infections, and disease burden due to CPE is also on the rise globally. Nevertheless, only few studies have been conducted regarding CPE infection and its epidemiological factors in the Republic of Korea (ROK). In this paper, we analyzed clinical, microbiological, and epidemiological characteristics of CPE bloodstream infection (BSI) in ROK. Methods We designed retrospective cohort study by analyzing reports of epidemiological conducted by Epidemic Investigation Officers in KCDC from January 2015 to December 2016. CPE-infected cases were collected through the nationwide surveillance system. Numbers of sentinel surveillance hospitals included in the system were 100 hospitals in year 2015, and 115 hospitals in 2016. We selected cases with confirmed CPE BSI by Korea National Institute of Health that detected gene types of carbapenemase. Results Total of 131 CPE BSI were identified during the study period. Prevalence of CPE BSI among total CPE isolates was 7%. Nationwide, Klebsiella pneumoniae accounts for 69% of CPE BSI and 66% produced K. pneumoniae carbapenemase (KPC). The antibiotics susceptibility examination results showed that CPE prevalent in ROK had susceptibility to Amkacin, Tigecycline, or Gentamicin (76%, 41%, and 39%, respectively). Colistin sensitivity test was performed on only 29 patients, and 1 of those patients showed colistin resistance. 85% (111/131) of cases were classified to hospital acquired infections. Prevalence of CPE BSI among CPE isolates was 7% (131/2020). Most common BSI sources were lung (29%), primary (16%), and biliary tract (15%). Thirty-day mortality rate due to CPE BSI was 47.3%. A multivariable analysis showed that use of adequate antibiotics for CPE (p = 0.01) and APACHE II score (P < 0.001) at the time of CPE detection in the blood stream were significantly associated with decreased 30-day mortality. Conclusion CPE bacteremic episodes were already prevalent in the Republic of Korea. Moreover, most of CPE BSI originated from hospital acquired infection, pointing out the need for improvement of hospital infection control strategies. The use of adequate antibiotics therapies upon recognition of CPE infection could decrease mortality due to CPE blood stream infections. Disclosures All authors: No reported disclosures.

Background Cefiderocol (S-649266, CFDC) is a novel siderophore cephalosporin against Gram-negatives, including carbapenem (CR)-resistant strains. Its spectrum includes both the Enterobacteriaceae but also nonfermenters, including Stenotrophomonas maltophilia—an opportunistic pathogen with intrinsic resistance to carbapenem antibiotics. In this study, in vitro activity and in vivo efficacy of CFDC and comparators against S. maltophilia were determined. Methods MICs of CFDC and comparators (trimethoprim/sulfamethoxazole (TMP/SMX), minocycline (MINO), tigecycline (TGC), ciprofloxacin (CPFX), cefepime (CFPM), meropenem (MEPM), and colistin (CL)) were determined by broth microdilution method as recommended by CLSI. The MIC against CFDC was determined using iron-depleted cation-adjusted Mueller–Hinton broth. In vivo efficacy of CFDC, CFPM, ceftazidime–avibactam (CAZ/AVI), MEPM, and CL was evaluated using neutropenic murine systemic infection model caused by strain SR21970. The 50% effective doses (ED50s) were calculated by the logit method using the survival number at each dose 7 days after infection. Results MIC90 of CFDC and comparators against the 216 clinical isolates from global countries collected in SIDERO-CR 2014/2016 study are shown in the table. CFDC, TMP/SMX, MINO, and TGC showed good activity with MIC90 of 0.5, 0.25/4.75, 1, and 2 µg/mL, respectively. CFDC, MINO, and TGC inhibited growth of all tested strains at ≤1, ≤4, and ≤8 µg/mL although two strains showed resistance to TMP/SMX. MICs of CFPM, CAZ/AVI, MEPM, and CL were ≥32 µg/mL. The ED50 of CFDC against S. maltophilia SR21970 with MIC of 0.125 mg/mL was 1.17 mg/kg/dose. Conversely, MICs of CFPM, CAZ/AVI, MEPM/CS, and CL against SR21970 were 32 μg/mL or higher, and ED50s were >100 mg/kg/dose, showing that CFDC had potent in vivo efficacy against S. maltophilia strain which was resistant to other antibiotics. Conclusion CFDC showed potent in vitro activity against S. maltophilia, including TMP/SMX-resistant isolates. CFDC also showed potent in vivo efficacy reflecting in vitro activity against S. maltophilia in murine systemic infection model. Disclosures A. Ito, Shionogi & Co., Ltd.: Employee, Salary. M. Ota, Shionogi & Co., Ltd.: Employee, Salary. R. Nakamura, Shionogi & Co., Ltd.: Employee, Salary. M. Tsuji, Shionogi & Co., Ltd.: Employee, Salary. T. Sato, Shionogi & Co., Ltd.: Employee, Salary. Y. Yamano, Shionogi & Co., Ltd.: Employee, Salary.

Background PLZ is a next-generation aminoglycoside with structural modifications that protect it from aminoglycoside-modifying enzymes (AMEs) and in vitro activity against multidrug-resistant (MDR) Enterobacteriaceae, including aminoglycoside- and carbapenem-resistant strains. In the CARE study, PLZ was associated with improvement in 28-day all-cause mortality vs. CST in patients with CRE BSI. We report the microbiological outcomes in the CARE study by pathogen and key resistance mechanism. Methods CARE was a multinational, open-label trial that enrolled BSI patients with documented or presumed CRE into two cohorts. Patients in the randomized cohort received PLZ (15 mg/kg q24h IV) or CST (300-mg load [CST base activity] then 5 mg/kg/day IV) plus adjunctive tigecycline or meropenem. Patients in the observational cohort received PLZ plus investigator’s choice of adjunctive agent. Treatment duration was 7–14 days. Isolate identification and susceptibility testing were conducted by a central laboratory. Whole-genome sequencing was used to identify AME and carbapenemase genes. Microbiological outcomes were assessed in patients with confirmed CRE who received ≥1 dose of study drug (mMITT population). Results Of 45 BSI patients enrolled, 43 had confirmed CRE (mMITT), including Klebsiella pneumoniae (n = 42) and Enterobacter aerogenes (n = 1). Against CRE, PLZ MICs ranged from 0.12 to >128 µg/mL; 25/28 (89.3%) isolates from PLZ-treated patients had a PLZ MIC ≤4 µg/mL, while 3 had a PLZ MIC ≥128 µg/mL and a confirmed 16S ribosomal methyltransferase gene. CST MICs ranged from 0.25 to >128 µg/mL; 6/16 (37.5%) isolates from CST-treated patients had an MIC >2 µg/mL. There were 47 distinct Enterobacteriaceae pathogens isolated from 43 patients, and of these, AME genes were detected in 43/47 (91.5%), most commonly aac(6’)-Ib (n = 29). Carbapenemase genes were detected in 45/47 (95.7%) isolates, most commonly blaKPC (n = 33). PLZ demonstrated higher microbiological eradication rates than CST against CRE, including AME- and carbapenemase-producing isolates (table). Conclusion The results provide evidence of the efficacy of PLZ-based therapy for patients with BSI due to MDR Enterobacteriaceae, including AME- and carbapenemase-producing organisms. Disclosures A. W. Serio, Achaogen, Inc.: Employee and Shareholder, Salary. A. Smith, Achaogen, Inc.: Employee and Shareholder, Salary. K. M. Krause, Achaogen, Inc.: Employee, Salary. I. Galani, Achaogen, Inc.: Scientific Advisor, Research funding and honoraria. MSD: Scientific Advisor, Honoraria. A. C. Gales, MSD: Consultant and Speaker, Consulting fee. Pfizer: Consultant and Speaker, Consulting fee. BD: Consultant, Consulting fee. Bayer: Consultant, Consulting fee. A. Jubb, Achaogen, Inc.: Employee and Shareholder, Salary. L. E. Connolly, Achaogen, Inc.: Consultant, Consulting fee.

Background Omadacycline is a novel aminomethylcycline that recently completed Phase 3 clinical trials for the treatment of acute bacterial skin and skin structure infections (ABSSSIs) and community-acquired bacterial pneumonia (CABP). This study evaluated the activity of omadacycline against a broad collection of recent (2016) clinical isolates with molecularly characterized tetracycline resistance mechanisms. Methods A total of 177 Gram-positive and -negative clinical isolates were identified as carrying acquired tetracycline resistance genes and were included in this study. Isolates were previously subjected to next-generation sequencing followed by screening of known tetracycline resistance mechanisms. Susceptibility testing and interpretation were performed according to CLSI methods. Results Omadacycline demonstrated MIC50 values of 0.06–0.12 µg/mL against Gram-positive isolates carrying tet genes. Similar MIC results (0.06–0.12 µg/mL) were obtained against Gram-positive organisms carrying tet(K), tet(L)/tet(M) or tet(M). Omadacycline (MIC50/90, 0.12/0.25 µg/mL) and tigecycline (MIC50/90, 0.06/0.25 µg/mL) showed similar MIC results when tested against Staphylococcus aureus carrying tet(K). While tetracycline was less active (0.0–78.6% susceptible) against Tet(K)-producing S. aureus, doxycycline (MIC50/90, 0.5/0.5 µg/mL; 100.0% susceptible) was active in vitro. Omadacycline (MIC90, 0.25–2 µg/mL) and tigecycline (MIC90, 0.12–1 µg/mL) showed potent MIC results against Gram-positive isolates carrying tet(L) and/or tet(M). Tetracycline and doxycycline had MIC90 values of ≥8 µg/mL. Omadacycline (MIC90 4–32 µg/mL) and tigecycline (MIC90 0.5–2 µg/mL) were active against Gram-negative isolates harboring tet(A), tet(B) or tet(D) or a combination of tet. Tetracycline (MIC50/90, >16/>16 µg/mL) and doxycycline (MIC50/90, >8/>8 µg/mL) had elevated MIC50 and MIC90 results against these isolates. Conclusion Results presented here indicate that omadacycline is not adversely affected by tet genes present in contemporary Gram-positive and -negative clinical isolates, a characteristic that differs from the legacy tetracycline agents. Disclosures R. E. Mendes, Paratek Pharmaceuticals: Research Contractor, Research support. M. Castanheira, Paratek Pharmaceuticals: Research Contractor, Research support. E. S. Armstrong, Paratek Pharmaceuticals: Employee, Salary. J. N. Steenbergen, Paratek Pharmaceuticals: Employee and Shareholder, Salary. R. K. Flamm, Paratek Pharmaceuticals: Research Contractor, Research support.

Background Clostridium difficile infection (CDI) is a significant cause of morbidity and mortality. IDSA guidelines recommend oral vancomycin (VAN) for the treatment of CDI, although doses used in practice vary substantially. The purpose of this study was to determine differences in outcomes between patients treated with high dose (HD; ≥250 mg four times daily [QID]) vs. standard dose (SD; 125 mg QID) VAN for CDI. Methods This multicenter study evaluated patients at two hospitals in Albany, NY diagnosed with CDI and treated with oral VAN between January 2013 and August 2017. Hospitalized patients were included if: age ≥18 years, positive C. difficile toxin polymerase chain reaction (PCR), symptomatic infection (e.g., new onset or increased frequency of loose stools), and received ≥48 hours of VAN QID. Patients were excluded if: received ≥48 hours of metronidazole prior to VAN initiation, VAN per rectum, required surgical intervention ≤48 hours from PCR, had a history of fecal microbiota transplant, received ≥1 dose of fidaxomicin or tigecycline prior to or within 48 hours from PCR, or died ≤48 hours from PCR. The primary outcome was 90-day CDI recurrence; secondary outcomes included 30-day all-cause mortality and 90-day readmission. Variables with a P-value Results Four hundred fifty-eight patients were included (site 1: 270; site 2: 188). Two hundred twenty-four patients received SD VAN (48.9%); 234 received HD VAN [250 mg QID: 199 (43.5%); 500 mg QID: 35 (7.6%)]. Baseline demographics were similar between groups. Patients treated with HD were more likely to present with colitis (19.2 vs. 29.5%, P = 0.01) and have higher infection severity based on IDSA (P < 0.01), Zar (P < 0.01), and American College of Gastroenterology (P < 0.02) criteria. Modified APACHE II scores were similar between SD and HD groups (median: 12.2 vs. 12.9, P = 0.17). MV analysis identified no difference in 90-day recurrence with HD (OR 1.65, P = 0.13) after controlling for solid tumor cancers, immunosuppression, and IDSA severity. Similarly, no significant differences between SD and HD were observed for 30-day mortality and 90-day readmission. Conclusion No differences in recurrence, mortality, or readmission were identified between SD and HD oral VAN for the treatment of CDI, though HD VAN patients primarily received 250 mg QID. Disclosures All authors: No reported disclosures.

Background Colistin has re-emerged as last line antimicrobial to combat MDR GNB. There is need for robust pharmacokinetic (PK) and pharmacodynamics (PD) data to guide dosing. This study assessed the PK of CMS and colistin and its impact on clinical cure (CC) and acute kidney injury (AKI) in critically ill patients with normal baseline renal function. Methods Adult critically ill patients with colistin susceptible MDR/XDR infections and normal renal function who were treated with intravenous CMS (9MU CMS loading dose (LD) followed by maintenance (MD) 3MU every 8 hour starting 24 hours after LD) were recruited into this prospective observational study. For PK sampling, 3mL venous blood was drawn immediately before LD and at 0.5, 1, 2, 4, 8 and 12 hours after LD. During MD, samples were collected before and at 1, 2 and 8 hours after the eight and nineth infusion. Colistin plasma concentrations were determined by LC–MS. Results A total of 280 serum samples were analyzed from 20 patients. Sixty percent had pneumonia. Predominant pathogens were Klebsiella pneumonia (12) and Acinetobacter spp. (8). Mean creatinine clearance (CrCl) was 115 ± 24 mL/minute (72.3–208.8). All patients received combination therapy with colistin, 18(90%) received meropenem and 5(25%) received tigecycline. Clinical cure rate was 50% (10/20) and mortality rate was 25% (5/20). Mean LD colistin Cmax were 3 ± 1.1 mg/L (1.75–5.14) and 2.37 ± 1.2 mg/L (1.52–5.54) among CC and CF groups, respectively (P = 0.13). MD colistin Css avg was 2.25 ± 1.3 mg/L and 1.78 ± 1.1 mg/L in CC and CF groups, respectively. The mean AUC0–24/MIC ratio of MD colistin was 92.76 ± 65.5 and 76.59 ± 51.8 for CC and CF groups, respectively (P = 0.27). In pneumonia, AUC0–24/MIC for Acinetobacter spp. was higher in the CC (71.18 ± 10.20) than in the CF group (40.88 ± 16.28) (P = 0.05). Renal injury was 5% at 7 days and 40% at end of therapy. Ten to 20% of patients with CrCl ≥ 100 mL/minute had Css avg ≥ 2 mg/L. Majority of CF with AKI had Css avg between 1 and 1.5 mg/L Conclusion Clinical cure was low at 50%. Sub-inhibitory Css avg and increased volume of distribution following MD could have contributed to high failure. Colistin exposures were similar to those reported in other published cohorts with no consistent exposure-response relationship. Based on these results, there is an important role for therapeutic drug monitoring with Colistin. Disclosures All authors: No reported disclosures.

Background In Gram-negative bacteremia (GNB), administrative data suggest that “difficult-to-treat resistance” (DTR; i.e., co-resistance to all first-line antibiotics) increases mortality. However, adequate risk-adjustment for severity of illness (SOI) may require granular laboratory and physiologic data. Methods Adult inpatients with GNB were identified from electronic health records (EHRs) of 140 hospitals in the Cerner Healthfacts database between 2009 and 2015. Mortality from DTR (intermediate/resistant in vitro to β-lactams including carbapenems and fluoroquinolones) was compared with GNB phenotypes susceptible to at least one first-line agent, but otherwise resistant to carbapenems (CR), extended-spectrum cephalosporins (ECR), or fluoroquinolones (FQR) per US Centers for Disease Control and Prevention surveillance definitions. Relative risk of mortality was adjusted (aRR) for age, sex, baseline Sequential Organ Failure Assessment (SOFA) score, Elixhauser comorbidity index, GNB source, taxon, hospital vs. community onset, year, and hospital region, bed capacity, and urban and teaching status using Poisson regression. Results Of 25,448 unique GNB encounters, 207 (1%) met DTR criteria. DTR patients were 2-fold more likely to receive intravenous colistin and 5-fold more likely to receive tigecycline compared with CR cases susceptible to ≥1 first-line agent. Crude mortality varied considerably by taxon and resistance phenotype, but resistance per se was associated with only a minority of overall deaths (DTR = 3% of deaths; any of the four resistance phenotypes = 28% of deaths; Figure 1). Inclusion of EHR-derived, baseline SOFA scores in SOI adjustments decreased aRR effect estimates; nonetheless, all resistance phenotypes still significantly increased mortality (Figure 2A). Among resistance phenotypes, aRR of mortality was similar for DTR vs. CR (aRR = 1.18; 95% CI, 0.91–1.54; P = 0.2), but higher for DTR vs. ECR (aRR = 1.26 [1.01–1.58]; P = 0.04), and DTR vs. FQR (aRR = 1.36 [1.08–1.70]; P = 0.008), respectively (Figure 2B). Conclusion DTR is associated with nonsurvival and greater use of reserve antibiotics in GNB, but adds little to the risk of death associated with CR. The impact of resistance on survival is attenuated but still present even after risk adjustment using granular clinical data. Disclosures All authors: No reported disclosures.

Sir, Anthony R. White, on behalf of the BSAC Working Party on The Urgent Need: Regenerating Antibacterial Drug Discovery and Development, has reviewed the economics of antibacterial resistance and its control.1 In this letter, we add to the current knowledge base on this issue by providing a historical perspective on the public health need for antibacterial agents active against emerging multidrug-resistant bacteria and the sales of selected agents, chosen as examples, that responded to this need in previous decades. Data on the worldwide sales of these agents and their dates of approval in the USA were obtained from MedAdNews (http://www.pharmalive.com/med-ad-news), as well as companies’ annual reports (Figure 1). Figure 1. Worldwide sales of patented antibacterial agents chosen as examples, 1985–2012. These agents targeted multidrug-resistant bacteria that were prevalent at the time of their launch. Data do not include sales of generic versions of the same agents ... In the mid-1980s, the rapid emergence of multidrug-resistant Gram-negative bacteria such as extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae2 and ceftazidime-resistant Pseudomonas aeruginosa3 highlighted the need for antibacterial agents active against these resistant bacteria. Imipenem/cilastatin, the first carbapenem, was approved in 1985 and immediately responded to this need. From the mid-1980s into the 1990s, imipenem/cilastatin was used to treat patients infected with such multidrug-resistant Gram-negative bacteria (Figure 1). Meropenem, a second carbapenem, was approved in 1996 and its sales rapidly increased. In 2013, meropenem and imipenem/cilastatin are still essential antibacterial agents for the treatment of healthcare-associated infections, especially in severely ill or immunocompromised patients.4,5 Both are classified by the WHO as critically important antimicrobials in human medicine.6 During the last two decades, several other antibacterial agents active against emerging multidrug-resistant bacteria, and thus responding to the public health need, have reached substantial sales (Figure 1). Piperacillin/tazobactam, approved in 1993, found its market in the 2000s, in particular as an agent to treat healthcare-associated infections. Linezolid, approved in 2000 as the first oxazolidinone, and daptomycin, approved in 2003 as the first lipopeptide, quickly found their markets as agents to treat infections with Gram-positive bacteria, in particular methicillin-resistant Staphylococcus aureus. The sales of linezolid, which is available for both intravenous and oral use, should soon reach a similar level to that of ciprofloxacin in the late 1990s to early 2000s (Figure 1). The only exception to these trends may be tigecycline, approved in 2005 as the first glycylcycline, but did not yet reach annual worldwide sales of US$500 million (Figure 1). The increasing use of carbapenems, together with the varying quality of infection control practices, has led to the emergence of carbapenem-resistant Gram-negative bacteria. As early as the late 1980s, the percentage of P. aeruginosa isolates that were resistant to carbapenems started to increase.7 In 2007, the number of carbapenem-resistant P. aeruginosa infections in the European Union was estimated at 141 900 annually and the number of multidrug-resistant P. aeruginosa infections in the USA at 72 250 annually.8,9 More recently, carbapenemase-producing Enterobacteriaceae have emerged and are now spreading globally, including in the European Union.10–13 The generally favoured option for the treatment of patients infected by multiresistant carbapenemase-producing bacteria is colistin, an old antibiotic that has now become an essential drug in hospitals. The consequence of the increasing use of colistin, however, is the inevitable rise of colistin resistance, with high percentages of resistance already occurring in K. pneumoniae infections in some European hospitals,14,15 leading to clinical situations where there is no straightforward option for treatment. In 2009, a joint report from the European Centre for Disease Prevention and Control and the European Medicines Agency, in a collaboration with ReAct—Action on Antimicrobial Resistance, highlighted the gap between increasing antimicrobial resistance in Europe and the urgent need for new antibacterial agents active against resistant bacteria, in particular to treat multidrug-resistant Gram-negative infections.8 Although comparable to the need for agents to treat patients with multidrug-resistant Gram-negative infections (in particular those caused by ESBL-producing bacteria) in the mid-1980s and the 1990s, the current public health need for new antibacterial agents is still currently not being addressed. The succession of cycles of public health need followed by antibacterial productivity, as illustrated by White,1 that prevailed since the discovery of antibiotics seems to have come to a halt. Two recent reviews of the antibacterial research and development pipeline confirm that, despite some progress, there are currently only a few compounds in development with activity against multidrug-resistant Gram-negative bacteria, in particular metallo-carbapenemase (e.g. New Delhi metallo-β-lactamase)-producing Enterobacteriaceae or P. aeruginosa, or against multidrug-resistant Acinetobacter spp.16,17 This historical perspective shows that, in the presence of a public health need, antibacterial agents that targeted emerging multidrug-resistant bacteria quickly found their market and reached annual worldwide sales of US$500 million or above, sometimes reaching the ‘blockbuster’ threshold of US$1 billion for worldwide sales annually before the 10th full year after their launch (Figure 1). This observation goes against the common view that new antibacterial agents have a small potential market of less than US$500 million annually.18 It provides an insight into what would be the potential market, considering the current public health need and current economic model,1 for a novel antibacterial agent active against carbapenem-resistant Gram-negative bacteria.

Oritavancin is a novel lipoglycopeptide with activity against Gram-positive organisms including streptococci, methicillin-resistant Staphylococcus aureus, vancomycin-resistant S aureus (VRSA), and vancomycin-resistant enterococci (VRE) [1–3]. The US Food and Drug Administration approved oritavancin as a single intravenous dose of 1200 mg for the treatment of acute bacterial skin and skin structure infections on the basis of 2 clinical trials demonstrating noninferiority compared with vancomycin [4, 5]. There are limited options for treatment of serious VRE infections. Monotherapy with daptomycin or tigecycline or linezolid may be sufficient in some cases, but combination therapy is often indicated for severe or complicated infections such as endocarditis. Several antibiotic combinations have been used in isolated case reports with some efficacy, including the following: high-dose ampicillin with an aminoglycoside [6], ampicillin with ceftriaxone or imipenem [7, 8], high-dose daptomycin with ampicillin and gentamicin [9] or with gentamicin and rifampin [10], daptomycin with tigecycline [11, 12], quinupristin-dalfopristin with high-dose ampicillin [13] or doxycycline and rifampin [14], and linezolid with tigecycline [15]. The limited efficacy, limited susceptibility, and extensive toxicities with many of these agents and combinations present barriers to effective treatment. Additional treatment options for VRE endocarditis would be valuable. Although oritavancin has been shown to have in vitro activity against some isolates of VRE, clinical data are lacking. We describe the first use of a prolonged course of oritavancin in the treatment of a serious VRE infection, prosthetic valve endocarditis.

Background Overthe use of antibiotics has been associated with the emergence of antibiotic resistance. This study aims to evaluate trends in antibiotic utilization as defined by days of therapy per 1000 patient-days (DOT/1000 PD) in various community hospitals across the US. Methods Eighteen network hospitals provided antibiotic utilization data (2012–2016) on overall antibiotic use and the following classes: narrow-spectrum β-lactams (ampicillin, nafcillin, oxacillin, cefazolin, and cephalexin), non-carbapenem antipseudomonal β-lactams (piperacillin/tazobactam, ceftazidime, and cefepime), carbapenems, anti-methicillin-resistant Staphylococcus aureus (MRSA) agents (vancomycin, linezolid, daptomycin, and tigecycline), and fluoroquinolones. Antibiotic utilization and change in utilization trend during the study period was calculated using linear regression (β coefficient). Results Hospitals were primarily urban (72%) with an average of 209 total beds and 22 ICU beds. All hospitals have antimicrobial stewardship programs (ASPs) established during the study period. A decrease in antipseudomonal B-lactams and fluoroquinolones was observed during the study period, all other antibiotic classes had increased use (Table). Conclusion Overall antibiotic utilization increased over five years, particularly carbapenems and anti-MRSA agents with the highest utilization being reported with the latter. Efforts are needed to halt or decrease the use of these broad spectrum antimicrobials. Disclosures All authors: No reported disclosures. Antibiotic Class Mean Utilization (Range), DOT/1000 PD Mean β Coefficient All Antibiotics 62.3 (49.4–80.6) 2.7 Narrow-spectrum β-lactams 122.8 (64.5–207.2) 18 Antipseudomonal β-lactams * 129.6 (35–191.6) -1.2 Carbapenems 46.7 (145–82) 2.7 Anti-MRSA 156.9 (84.7–272.3) 5.5 Fluoroquinolones 151.9 (88.5–207.6) -2.6 *Excluding carbapenems

Background PLZ is a next-generation aminoglycoside with potent in vitro activity against multidrug- and carbapenem-resistant EB. The objective of this study was to assess the efficacy of PLZ human-simulated exposure, alone and in combination with MEM or TGC, against EB in the I+ murine septicemia model. Methods ICR mice were inoculated intraperitoneally with bacterial suspensions of 10 6.5 CFU/mL. Eight EB isolates with PLZ, MEM and TGC MICs ranging from 2 to 16, ≤0.015 to >32, and ≤0.06 to 2 mg/L, respectively, were utilized to assess the efficacy of PLZ alone or in combination against isolates at the upper end of PLZ MIC distribution. PLZ, MEM and TGC doses in mice that mimic the human plasma exposures following the administration of the clinical doses summarized in the table were utilized. Drug Human Dose PLZ 15 mg/kg Q24H, 0.5 h infusion MEM 2 g Q8H, 3 hours infusion TGC 50 mg Q12H Treatment mice were administered PLZ, MEM or TGC human-equivalent doses alone or in combinations of PLZ/MEM and PLZ/TGC, while control mice were administered vehicle. Treatments were initiated 1 hours post-infection and continued for 24 hours. Efficacy was assessed by survival through 96 hours. Survival was compared using Kaplan-Meier analysis and log-rank test. Results Compared with controls, human-simulated exposure of PLZ monotherapy produced significant improvement in survival for all isolates (P < 0.05) and resulted in overall survival percentages of 86 (n = 50) and 53.3 (n = 30) for isolates with MIC ≤4 and ≥8 mg/L, respectively (P < 0.05). Survival of MEM and TGC groups correlated well with their respective susceptibilities, with incremental increase in survival observed at lower MIC values. For isolate KP 561 (PLZ, MEM and TGC MICs of 8, >32 and 2 mg/L, respectively), PLZ/MEM and PLZ/TGC showed significant reduction in mortality compared with any of the single agents (P < 0.05) (Fig 1). Conclusion PLZ monotherapy resulted in improved survival in the I+ murine septicemia model, notably for isolates with MIC ≤4. Moreover, some evidence suggests that co-administration of MEM or TGC could potentially lead to further improvement in survival. These preclinical data utilizing clinically relevant exposures support a role for PLZ in the management of septicemia due to EB, including carbapenem-resistant isolates. Disclosures A. Kim, Achaogen, Inc.: Employee, Salary and Stock; K. M. Krause, Achaogen, Inc: Employee, Salary; D. P. Nicolau, Achaogen, Inc.: Grant Investigator, Research grant and Research support

Background Infections caused by carbapenem resistant Enterobacteriaceae (CRE) are associated with high mortality. Optimal treatment for CRE bacteremia remains unclear, including the role of combination therapy, carbapenem-containing regimens, or newer antimicrobials, such as ceftazidime-avibactam (CAZ-AVI). The objective of this study was to evaluate risk factors associated with mortality in patients with CRE bacteremia, with a focus on antimicrobial therapy. Methods This was a multicenter, retrospective cohort study of inpatients within Carolinas HealthCare System who had a positive blood culture with CRE (Klebsiella spp., Enterobacter spp., or Escherichia coli) between January 1, 2010 and September 30, 2016. CRE isolates were identified as pathogens with an ertapenem MIC ≥ 1 mcg/mL. The primary endpoint was death within 28 days after the first positive blood culture in patients with CRE bacteremia. Clinical variables, including the use of specific antimicrobials and combination therapy, were compared between 28-day survivors vs. non-survivors. Results A total of 73 patients were included with CRE bacteremia. The most common sources of infection identified were urine (42.5%) and intra-abdominal (38.4%). The overall 28-day mortality was 26%. Fifty-three (72.6%) patients received combination antibiotic therapy and 20 (27.4%) received monotherapy. Combination therapy with in vitro active agents (36.8% vs. 33.3%, P = 0.87) and the use of carbapenem-containing regimens (47.4% vs. 46.3%, P = 0.74) did not differ between those who died and survived, respectively. One patient treated with CAZ-AVI as monotherapy died, but only eight patients received this antibiotic. There was a trend towards higher use of tigecycline in the group that died compared with the group that survived (73.7% vs. 59.3%, P = 0.26). Conclusion There did not appear to be a difference in mortality at 28 days with the use of combination therapy or a carbapenem-containing regimen. While a statistically significant difference was not demonstrated, tigecycline-containing regimens may be associated with increased mortality in the treatment of CRE bacteremia. Larger prospective studies are necessary to further elucidate the role of combination therapy and newer agents, such as CAZ-AVI, in this patient population. Disclosures C. Polk, The Medicines Company: Investigator, Research support.

AdeR-AdeS is a two-component regulatory system, which controls expression of the adeABC efflux pump involved in Acinetobacter baumannii multidrug resistance. AdeR is a response regulator consisting of an N-terminal receiver domain and a C-terminal DNA-binding-domain. AdeR binds to a direct-repeat DNA in the intercistronic region between adeR and adeABC. We demonstrate a markedly high affinity binding between unphosphorylated AdeR and DNA with a dissociation constant of 20 nM. In addition, we provide a 2.75 angstrom crystal structure of AdeR DNA-binding-domain complexed with the intercistronic DNA. This structure shows that the alpha 3 and beta hairpin formed by beta 5-beta 6 interacts with the major and minor groove of the DNA, which in turn leads to the introduction of a bend. The AdeR receiver domain structure revealed a dimerization motif mediated by a gearwheel-like structure involving the D108F109-R122 motif through cation pi stack interaction. The structure of AdeR receiver domain bound with magnesium indicated a conserved Glu19Asp20-Asp63 magnesium-binding motif, and revealed that the potential phosphorylation site Asp63(OD1) forms a hydrogen bond with Lys112. We thus dissected the mechanism of how AdeR recognizes the intercistronic DNA, which leads to a diverse mode of response regulation. Unlocking the AdeRS mechanism provides ways to circumvent A. baumannii antibiotic resistance.