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Background Antimicrobial susceptibility testing (AST) is not routinely performed for Clostridioides difficile and data evaluating minimum inhibitory concentrations (MICs) are limited. We performed AST and whole genome sequencing (WGS) for 593 C. difficile isolates collected between 2012 and 2017 through the Centers for Disease Control and Prevention's Emerging Infections Program. Methods MICs to 6 antimicrobial agents (ceftriaxone, clindamycin, meropenem, metronidazole, moxifloxacin, and vancomycin) were determined using the reference agar dilution method according to Clinical and Laboratory Standards Institute guidelines. Whole genome sequencing was performed on all isolates to detect the presence of genes or mutations previously associated with resistance. Results Among all isolates, 98.5% displayed a vancomycin MIC ≤2 μg/mL and 97.3% displayed a metronidazole MIC ≤2 μg/mL. Ribotype 027 (RT027) isolates displayed higher vancomycin MICs (MIC50: 2 μg/mL; MIC90: 2 μg/mL) than non-RT027 isolates (MIC50: 0.5 μg/mL; MIC90: 1 μg/mL) (P <.01). No vanA/B genes were detected. RT027 isolates also showed higher MICs to clindamycin and moxifloxacin and were more likely to harbor associated resistance genes or mutations. Conclusions Elevated MICs to antibiotics used for treatment of C. difficile infection were rare, and there was no increase in MICs over time. The lack of vanA/B genes or mutations consistently associated with elevated vancomycin MICs suggests there are multifactorial mechanisms of resistance. Ongoing surveillance of C. difficile using reference AST and WGS to monitor MIC trends and the presence of antibiotic resistance mechanisms is essential. [ABSTRACT FROM AUTHOR]

Background Penicillin and ciprofloxacin are important for invasive meningococcal disease (IMD) management and prevention. IMD cases caused by penicillin- and ciprofloxacin-resistant Neisseria meningitidis containing a ROB-1 β-lactamase gene (blaROB-1) and a mutated DNA gyrase gene (gyrA) have been recently reported in the United States. Methods We examined 2097 meningococcal genomes collected through US population-based surveillance from January 2011 to February 2020 to identify IMD cases caused by strains with blaROB-1- or gyrA-mediated resistance. Antimicrobial resistance was confirmed phenotypically. The US isolate genomes were compared to non-US isolate genomes containing blaROB-1. Interspecies transfer of ciprofloxacin resistance was assessed by comparing gyrA among Neisseria species. Results Eleven penicillin- and ciprofloxacin-resistant isolates were identified after December 2018; all were serogroup Y, sequence type 3587, clonal complex (CC) 23, and contained blaROB-1 and a T91I-containing gyrA allele. An additional 22 penicillin-resistant, blaROB-1- containing US isolates with wild-type gyrA were identified from 2013 to 2020. All 33 blaROB-1-containing isolates formed a single clade, along with 12 blaROB-1-containing isolates from 6 other countries. Two-thirds of blaROB-1-containing US isolates were from Hispanic individuals. Twelve additional ciprofloxacin-resistant isolates with gyrA T91 mutations were identified. Ciprofloxacin-resistant isolates belonged to 6 CCs and contained 10 unique gyrA alleles; 7 were similar or identical to alleles from Neisseria lactamica or Neisseria gonorrhoeae. Conclusions Recent IMD cases caused by a dual resistant serogroup Y suggest changing antimicrobial resistance patterns in the United States. The emerging dual resistance is due to acquisition of ciprofloxacin resistance by β-lactamase-containing N. meningitidis. Routine antimicrobial resistance surveillance will effectively monitor resistance changes and spread. [ABSTRACT FROM AUTHOR]

Background: Aztreonam/avibactam is a combination agent that shows promise in treating infections caused by highly antibiotic-resistant MBL-producing Enterobacterales. This combination can be achieved by combining two FDA-approved drugs: ceftazidime/avibactam and aztreonam. It is unknown whether ceftazidime in the combination ceftazidime/aztreonam/avibactam has a synergistic or antagonistic effect on the in vitro activity of aztreonam/avibactam by significantly increasing or decreasing the MIC.Objectives: To determine whether increasing ceftazidime concentrations affect the MICs of aztreonam/avibactam alone.Methods: A custom 8 × 8 chequerboard broth microdilution (BMD) panel was made using a digital dispenser (Hewlett-Packard, Corvallis, OR, USA). The panel included orthogonal 2-fold dilution series of aztreonam and ceftazidime ranging from 0.5 to 64 mg/L. Avibactam concentration was kept constant at 4 mg/L throughout the chequerboard. Thirty-seven Enterobacterales isolates from the CDC & FDA Antibiotic Resistance Isolate Bank or CDC's internal collection with intermediate or resistant interpretations to aztreonam and ceftazidime/avibactam were included for testing. All isolates harboured at least one of the following MBL genes: blaIMP, blaNDM or blaVIM.Results: Regardless of the concentration of ceftazidime, aztreonam/avibactam with ceftazidime MICs for all 37 isolates were within one 2-fold doubling dilution of the aztreonam/avibactam MIC.Conclusions: Ceftazidime, in the combination ceftazidime/avibactam/aztreonam, did not affect the in vitro activity of aztreonam/avibactam in this sample of isolates. These findings can help assure clinical and public health laboratories that testing of aztreonam/avibactam by BMD can act as a reliable surrogate test when the combination of ceftazidime/avibactam and aztreonam is being considered for treatment of highly antibiotic-resistant MBL-producing Enterobacterales. [ABSTRACT FROM AUTHOR]

Background Previous reports suggested that US methicillin-resistant Staphylococcus aureus (MRSA) strain epidemiology has changed since the rise of USA300 MRSA. We describe invasive MRSA trends by strain type. Methods Data came from 5 Centers for Disease Control and Prevention Emerging Infections Program sites conducting population-based surveillance and collecting isolates for invasive MRSA (ie, from normally sterile body sites), 2005–2013. MRSA bloodstream infection (BSI) incidence per 100 000 population was stratified by strain type and epidemiologic classification of healthcare exposures. Invasive USA100 vs USA300 case characteristics from 2013 were compared through logistic regression. Results From 2005 to 2013, USA100 incidence decreased most notably for hospital-onset (6.1 vs 0.9/100 000 persons, P <.0001) and healthcare-associated, community-onset (10.7 vs 4.9/100 000 persons, P <.0001) BSIs. USA300 incidence for hospital-onset BSIs also decreased (1.5 vs 0.6/100 000 persons, P <.0001). However, USA300 incidence did not significantly change for healthcare-associated, community-onset (3.9 vs 3.3/100 000 persons, P =.05) or community-associated BSIs (2.5 vs 2.4/100 000 persons, P =.19). Invasive MRSA was less likely to be USA300 in patients who were older (adjusted odds ratio [aOR], 0.97 per year [95% confidence interval {CI},.96–.98]), previously hospitalized (aOR, 0.36 [95% CI,.24–.54]), or had central lines (aOR, 0.44 [95% CI,.27–.74]), and associated with USA300 in people who inject drugs (aOR, 4.58 [95% CI, 1.16–17.95]). Conclusions Most of the decline in MRSA BSIs was from decreases in USA100 BSI incidence. Prevention of USA300 MRSA BSIs in the community will be needed to further reduce burden from MRSA BSIs. [ABSTRACT FROM AUTHOR]

Background Few data suggest that Clostridioides difficile infections (CDIs) detected by toxin enzyme immunoassay (EIA) are more severe and have worse outcomes than those detected by nucleic acid amplification tests (NAATs) only. We compared toxin- positive and NAAT-positive-only CDI across geographically diverse sites. Methods A case was defined as a positive C. difficile test in a person ≥1 year old with no positive tests in the prior 8 weeks. Cases were detected during 2014–2015 by a testing algorithm (specimens initially tested by glutamate dehydrogenase and toxin EIA; if discordant results, specimens were reflexed to NAAT) and classified as toxin positive or NAAT positive only. Medical charts were reviewed. Multivariable logistic regression models were used to compare CDI-related complications, recurrence, and 30-day mortality between the 2 groups. Results Of 4878 cases, 2160 (44.3%) were toxin positive and 2718 (55.7%) were NAAT positive only. More toxin-positive than NAAT-positive-only cases were aged ≥65 years (48.2% vs 38.0%; P <.0001), had ≥3 unformed stools for ≥1 day (43.9% vs 36.6%; P <.0001), and had white blood cell counts ≥15 000 cells/µL (31.4% vs 21.4%; P <.0001). In multivariable analysis, toxin positivity was associated with recurrence (adjusted odds ratio [aOR], 1.89; 95% confidence interval [CI], 1.61–2.23), but not with CDI-related complications (aOR, 0.91; 95% CI,.67–1.23) or 30-day mortality (aOR, 0.95; 95% CI,.73–1.24). Conclusions Toxin-positive CDI is more severe, but there were no differences in adjusted CDI-related complication and mortality rates between toxin-positive and NAAT-positive-only CDI that were detected by an algorithm that utilized an initial glutamate dehydrogenase screening test. [ABSTRACT FROM AUTHOR]

Objectives: To understand the molecular epidemiology of gentamicin-resistant Campylobacter and investigate aminoglycoside resistance mechanisms. Methods: One-hundred-and-fifty-one gentamicin-resistant Campylobacter isolates from humans (n=38 Campylobacter jejuni; n=41, Campylobacter coli) and retail chickens (n=72 C. coli), were screened for the presence of gentamicin resistance genes by PCR and subtyped using PFGE. A subset of the isolates (n=41) was analysed using WGS. Results Nine variants of gentamicin resistance genes were identified: aph(2)-Ib, Ic, Ig, If, If1, If3, Ih, aac(6')-Ie/aph(2)-Ia and aac(6')-Ie/aph(2)-If2. The aph(2)-Ib, Ic, If1, If3, Ih and aac(6')-Ie/aph(2)-If2 variants were identified for the first time in Campylobacter. Human isolates showed more diverse aminoglycoside resistance genes than did retail chicken isolates, in which only aph(2)-Ic and -Ig were identified. The aph(2)-Ig gene was only gene shared by C. coli isolates from human (n=27) and retail chicken (n=69). These isolates displayed the same resistance profile and similar PFGE patterns, suggesting that contaminated retail chicken was probably the source of human C. coli infections. Human isolates were genetically diverse and generally more resistant than the retail chicken isolates. The most frequent co-resistance was to tetracycline (78/79, 98.7%), followed by ciprofloxacin/nalidixic acid (46/79, 58.2%), erythromycin and azithromycin (36/79, 45.6%), telithromycin (32/79, 40.5%) and clindamycin (18/79, 22.8%). All human and retail meat isolates were susceptible to florfenicol. Conclusions: This study demonstrated that several new aminoglycoside resistance genes underlie the recent emergence of gentamicin-resistant Campylobacter, and that, in addition to contaminated retail chicken, other sources have also contributed to gentamicin-resistant Campylobacter infections in humans. [ABSTRACT FROM AUTHOR]

Skin infections are frequently caused by Staphylococcus aureus and can lead to a fatal sepsis. The microbial mechanisms controlling the initiation and progression from mild skin infection to a severe disseminated infection remain poorly understood. Using a combination of clinical data and in vitro and ex vivo assays, we show that staphylokinase, secreted by S. aureus, promoted the establishment of skin infections in humans and increased bacterial penetration through skin barriers by activating plasminogen. However, when infection was established, the interaction between staphylokinase and plasminogen did not promote systemic dissemination but induced the opening and draining of abscesses and decreased disease severity in neutropenic mice. Also, increased staphylokinase production was associated with noninvasive S. aureus infections in patients. Our results point out the dual roles of staphylokinase in S. aureus skin infections as promoting the establishment of infections while decreasing disease severity. [ABSTRACT FROM PUBLISHER]

In this article, the authors discuss the study that characterizes the properties of the human gut microbes in gnotobiotic mice. It discusses the methods for establishing and propagating inbred strains of mice under germ-free (GF) conditions. The authors provide an overview of the methods use in studying the complex microbial communities in gnotobiotic mice. It argues that community genetics provide powerful technology to dissect the operations of microbial communities.

Background Carbapenemases, a global health threat, are a diverse group of β-lactamases active against cephalosporins and carbapenems, which are often last resort treatments for multidrug-resistant gram-negative infections. The most common carbapenemases reported among Pseudomonas aeruginosa are metallo-β-lactamase (MBLs). We describe a novel MBL (designated HMB-2) identified in a P. aeruginosa isolate from a urine specimen collected in 2015 as part of CDC's Emerging Infections Program. Methods We performed antimicrobial susceptibility testing (AST) by broth microdilution, real-time PCR to screen for common carbapenemases (IMP, KPC, NDM, VIM, and OXA-48), and modified carbapenem inactivation method (mCIM) to test for carbapenemase production. The isolate underwent whole-genome sequencing (WGS) using Illumina MiSeq and PacBio RS II (Pacific Biosciences) platforms. Long read sequences were polished using Quiver and corrected by Pilon utilizing Illumina reads. We further characterized a putative novel MBL identified in WGS data by amplifying and cloning the gene into the pCR2.1-TOPO II vector (Invitrogen), which was then sub-cloned into a pET21 expression vector (Sigma–Aldrich). The resulting hmb2 + pET21 plasmid was transformed into a susceptible Escherichia coli for AST, including the imipenem-EDTA method to confirm MBL activity. Results The isolate displayed resistance to carbapenems and demonstrated phenotypic carbapenemase activity (mCIM positive), but was negative for carbapenemase genes by PCR. WGS analyses identified a putative MBL gene located on the chromosome. The gene shared 98% DNA and protein sequence identity with an MBL reported in 2016 in a P. aeruginosa isolate from Germany (HMB-1) and thus was named hmb -2. The cloned hmb -2 gene conferred resistance to carbapenems (meropenem and ertapenem) and third-generation cephalosporins (cefotaxime and ceftazidime) in transformed E. coli. The Minimum Inhibitory Concentrationratio for the imipenem-EDTA method was ≥4. Conclusion A putative, novel β-lactamase gene, bla HMB-2, was identified and cloned. The imipenem-EDTA results indicated that HMB-2 is an MBL. This discovery underscores the important role WGS plays in identifying new mechanisms of antimicrobial resistance. Disclosures All authors: No reported disclosures. [ABSTRACT FROM AUTHOR]

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 bla NDM-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 bla KPC-2 . The larger plasmid (354kbp) harbored 11 AR genes, including the metallo-β-lactamase gene bla NDM-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. [ABSTRACT FROM AUTHOR]

Colistin is increasingly being used to treat serious infections caused by multidrug-resistant Gram-negative bacteria. With the recent emergence of plasmid-mediated colistin resistance (mcr genes), screening for isolates with phenotypic colistin resistance has become clinically and epidemiologically relevant. However, antimicrobial susceptibility testing (AST) of colistin is associated with several technical challenges. Disk diffusion does not work because of poor diffusion of the large colistin molecule, Etest has been reported to underestimate minimum inhibitory concentration (MIC) values, and most clinical microbiology laboratories lack the capacity to perform broth microdilution (BMD). In this study, we compared the Etest method with the reference BMD method described by the Clinical and Laboratory Standards Institute (CLSI) for determining colistin MICs among Enterobacteriaceae. A total of 114 isolates of Enterobacteriaceae (51 carbapenem-resistant [CRE] and 63 carbapenem-susceptible [CSE]) were selected for colistin AST. One CRE isolate and 13 CSE isolates harbored a mcr gene. BMD testing was performed according to CLSI guidelines using a frozen reference panel with colistin concentrations ranging from 0.25 to 8 µg/mL. The Etest (BioMérieux, Durham, NC) method was performed on Mueller-Hinton agar (BBL, Becton Dickinson, Sparks, MD) according to the manufacturer's instructions. Interpretive criteria based on CLSI epidemiological cutoff values (non-wild-type ≥4 µg/mL; wild-type ≤2 µg/mL) were used to define resistance and susceptibility to colistin, respectively. By BMD, colistin MICs ranged from ≤0.25 to >8 µg/mL and 27% were determined to be colistin-resistant. The categorical agreement between Etest and BMD was 92%. All 14 mcr-positive isolates were categorized as colistin-resistant by BMD, while Etest classified 13/14 as resistant. In conclusion, clinical microbiology laboratories lacking capacity to perform BMD could implement the Etest method with BBL Mueller-Hinton agar for epidemiological purposes to help identify candidate isolates for mcr screening. To determine whether colistin can be used clinically, BMD would still be required. [ABSTRACT FROM AUTHOR]

Background Infections with metallo-β-lactamase (MBL)-producing organisms are emerging in the United States. Treatment options for these infections are limited. We describe MBL genes among carbapenemase positive carbapenem-resistant Enterobacteriaceae (CP-CRE) and Pseudomonas aeruginosa (CP-CRPA) isolates tested during the first two years of the Antibiotic Resistance Laboratory Network (AR Lab Network). Methods State and local public health laboratories tested CRE and CRPA isolates for organism identification, antimicrobial susceptibility, and PCR-based detection of bla KPC, bla NDM, bla OXA-48-like, bla VIM, and bla IMP carbapenemase genes. All testing results were sent to CDC at least monthly. Results Since January 2017, the AR Lab Network tested 21,733 CRE and 14,141 CRPA. CP-CRE were detected in 37% of CRE; 2% of CRPA were CP-CRPA. Among CP-CRE, 9% (686/8016) were MBL-producers (NDM, VIM, or IMP). Among MBL-producers, a bla NDM gene was detected most often (81%; 551/686). bla NDM were most common among Klebsiella spp. (47%; 261/551), bla IMP were most common among Providencia spp. (53%; 40/75), bla VIM was most common among Enterobacter spp. (19%; 25/62). Twelve percent (96) of MBL CP-CRE contained more than one carbapenemase gene. Among CP-CRPA, 73% (218/300) were MBL producers and bla VIM was the most common gene (62%; 186). Three (1%) MBL CP-CRPA contained more than one carbapenemase. Conclusion Increased testing of CRE and CRPA isolates through the AR Lab Network has facilitated early and rapid detection of hard-to-treat infections caused by MBL-producing organisms across the United States. The widespread distribution of MBL genes highlights the continued need for containment strategies that help prevent transmission between patients and among healthcare facilities. To support therapeutic decisions for severe infections caused by MBL-producing organisms, the AR Lab Network is now offering rapid susceptibility testing against aztreonam/avibactam, using digital dispenser technology. This testing program aims to close the gap between the availability of new drugs or drug combinations and the availability of commercial AST methods, thereby improving patient safety and antimicrobial stewardship. Disclosures All authors: No reported disclosures. [ABSTRACT FROM AUTHOR]

Background In 2009, the Centers for Disease Control and Prevention (CDC) implemented Clostridioides difficile infection (CDI) surveillance through the Emerging Infections Program (EIP) to monitor the incidence and evolving epidemiology of CDI in the United States. Since 2012, ribotypes (RTs) 027, 106, 002, 014, and 020 have constituted the top five strain types among both US community- and healthcare-associated isolates. Here we describe the changes in molecular epidemiology of C. difficile isolates collected in the United States in 2017. Methods In 2017, CDI surveillance was conducted at 10 EIP sites (CA, CO, CT, GA, MD, MN, NM, NY, OR, and TN). A convenience sample of clinical laboratories across EIP sites submitted C. difficile -positive stool specimens to the MN Department of Health Public Health Laboratory and Hines VA Hospital (IL) for culture. Isolates were forwarded to CDC and characterized by capillary-based PCR-ribotyping and PCR detection of tcdA , tcdB , cdtA , cdtB , and deletions in tcdC. Results In 2017, 1,051 C. difficile isolates were submitted; the total number of isolates received from each site ranged from 11 to 286 with a median of 85.5. In total, 143 RTs were observed, with the majority of isolates harboring toxin genes tcdA and tcdB (95%) and a wild-type tcdC sequence (71%). Among 556 healthcare-associated isolates, RT 027 was the most prevalent and the top RT at 5 sites (CA, GA, MD, NM, TN). Ribotype 106 was the most prevalent among 495 community-associated CA isolates and the top RT at 6 sites (CO, CT, GA, MD, MN, TN). Ribotype 027 significantly decreased from 2012 to 2017 among both healthcare-associated (21% vs 15%; p = 0.02) and community-associated isolates (17% vs 6%; P < 0.0001). Among healthcare-associated isolates, RT 076, which was observed in 8 EIP sites, increased from 2% in 2016 to 5% in 2017 (p = 0.05) and replaced RT 020 as one of the top 5 healthcare-associated RTs in 2017. Conclusion Despite an overall decline since 2012, RT 027 remained the most prevalent RT among healthcare-associated isolates submitted in 2017. The increased frequency of RT 076 among healthcare-associated isolates submitted in 2017 highlights the evolving molecular epidemiology of C. difficile and the need for continued surveillance to monitor potential emerging strains. Disclosures All authors: No reported disclosures. [ABSTRACT FROM AUTHOR]