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Objectives To investigate the molecular epidemiology and antimicrobial susceptibility of Clostridioides difficile isolates from patients with C. difficile infection (CDI) from two Phase 3 clinical trials of surotomycin. Methods In both trials [Protocol MK-4261-005 (NCT01597505) conducted across Europe, North America and Israel; and Protocol MK-4261-006 (NCT01598311) conducted across North America, Asia-Pacific and South America], patients with CDI were randomized (1:1) to receive oral surotomycin (250 mg twice daily) or oral vancomycin (125 mg four times per day) for 10 days. Stool samples were collected at baseline and C. difficile isolates were characterized by restriction endonuclease analysis (REA) and PCR ribotyping. Susceptibility testing was performed by agar dilution, according to CLSI recommendations. Results In total, 1147 patients were included in the microbiological modified ITT population. Of 992 recovered isolates, 922 (92.9%) were typed. There was a high association between REA groups and their corresponding predominant PCR ribotype (RT) for BI, DH, G and CF strains. REA group A showed more diverse PCR RTs. Overall, the most common strain was BI/RT027 (20.3%) followed by Y/RT014/020 (15.0%) and DH/RT106 (7.2%). The BI/RT027 strain was particularly prevalent in Europe (29.9%) and Canada (23.6%), with lower prevalence in the USA (16.8%) and Australia/New Zealand (3.4%). Resistance was most prevalent in the BI/RT027 strain, particularly to metronidazole, vancomycin and moxifloxacin. Conclusions A wide variation in C. difficile strains, both within and across different geographical regions, was documented by both REA and ribotyping, which showed overall good correlation.

Three strictly anaerobic strains of Escherichia coli were misidentified as Fusobacterium mortiferum, due to a deletion of the hemB gene which is involved in anaerobic respiration. An unusual antimicrobial susceptibility pattern sparked the further diagnostic strategies that eventually identified these strains as true anaerobic E. coli This phenomenon is more common than appreciated and can have an impact on clinical practice including persistent and relapsing infections.

The in vitro activity of 13 antimicrobials against clinical isolates of Gemella morbillorum showed good susceptibility to clindamycin, all beta-lactams agents studied except cefoxitin (MIC

Tedizolid’s anaerobic activity is unappreciated. In this study, it was active against all 332 anaerobic isolates tested at ≤2 μg/ml exceptBilophila wadsworthiaand was more active than linezolid againstBacteroides fragilisgroup species (MIC90, 1 μg/ml versus 2 to 4 μg/ml). Tedizolid was active against Gram-positive anaerobes (MIC90for clostridia, 0.25 to 1 μg/ml; MIC90for anaerobic cocci, ≤0.

Background Bezlotoxumab reduced rates of recurrent Clostridioides difficile infection (rCDI) vs placebo in Monoclonal Antibodies for C. difficile Therapy (MODIFY) I/II trial participants receiving antibacterial drug treatment for CDI. A secondary objective of MODIFY I/II was to assess bezlotoxumab’s efficacy against C. difficile strains associated with increased rates of morbidity and mortality. Methods In this post-hoc analysis of pooled MODIFY I/II data, efficacy endpoints were assessed in participants infected with restriction endonuclease analysis BI and non-BI strains of C. difficile at study entry. Treatment outcomes were compared between participants receiving bezlotoxumab (alone or with actoxumab [B, B+A]) and those receiving no bezlotoxumab (placebo or actoxumab [P, A]). Results From 2559 randomized participants, C. difficile was isolated from 1588 (67.2%) baseline stool samples. Participants with BI strains (n = 328) were older and had more risk factors for rCDI than non-BI strain participants (n = 1260). There were no differences in initial clinical cure rate between BI and non-BI strains in either group. The rCDI rate for BI strains treated with bezlotoxumab was lower than for the no bezlotoxumab group (B, B+A vs P, A: 23.6% vs 43.9%) and was also lower for the non-BI strains (B, B+A vs P, A: 21.4% vs 36.1%). Rates of 30-day CDI-associated rehospitalization were greater with BI vs non-BI strains in both groups. Conclusions Infection with BI strains of C. difficile predicted poor outcomes in the MODIFY I/II trials. Bezlotoxumab (alone or with actoxumab) treatment was effective both in BI and non-BI subpopulations.

To better characterize murine intestinal microbiota, a large number (187) of Gram-positive-staining, rod- and coccoid-shaped, and facultatively or strictly anaerobic bacteria were isolated from small and large intestinal contents from mice. Based on 16S rRNA gene sequencing, a total 115 isolates formed three phylogenetically distinct clusters located within the family Erysipelotrichaceae. Group 1, as represented by strain NYU-BL-A3T, was most closely related to Allobaculum stercoricanis, with 16S rRNA gene sequence similarity values of 87.7 %. A second group, represented by NYU-BL-A4T, was most closely related to Faecalibaculum rodentium, with 86.6 % 16S rRNA gene sequence similarity. A third group had a nearly identical 16S rRNA gene sequence (99.9 %) compared with the recently described Faecalibaculum rodentium, also recovered from a laboratory mouse; however, this strain had a few differences in biochemical characteristics, which are detailed in an emended description. The predominant (>10 %) cellular fatty acids of strain NYU-BL-A3T were C16 : 0 and C18 : 0, and those of strain NYU-BL-A4T were C10 : 0, C16 : 0, C18 : 0 and C18 : 1ω9c. The two groups could also be distinguished by multiple biochemical reactions, with the group represented by NYU-BL-A4T being considerably more active. Based on phylogenetic, biochemical and chemotaxonomic criteria, two novel genera are proposed, Ileibacterium valens gen. nov., sp. nov. with NYU-BL-A3T (=ATCC TSD-63T=DSM 103668T) as the type strain and Dubosiella newyorkensis gen. nov., sp. nov. with NYU-BL-A4T (=ATCC TSD-64T=DSM 103457T) as the type strain.

Due to increasing antibiotic resistance among anaerobic bacteria, routine antimicrobial susceptibility testing is recommended by the Clinical and Laboratory Standards Institute (CLSI). This study compared the minimum inhibitory concentrations (MICs) from 920 Clostridium difficile isolates tested against seven antimicrobial agents using the two current CLSI reference methodologies, agar dilution method, vs broth microdilution method. A subset of isolate testing was performed independently by two laboratories to evaluate reproducibility. A negative bias was noted for MICs generated from broth microdilution compared to agar dilution and the reproducibility was variable and drug dependent. Therefore, broth microdilution is not recommended as an alternative to agar dilution for C. difficile antimicrobial susceptibility testing.

The in vitro activity of DS-2969b, a novel GyrB inhibitor, and six comparator agents was studied against 101 recent North American Clostridioides difficile isolates, 46 other intestinal anaerobes and 51 strains of methicillin-resistant Staphylococcus aureus. The MIC ranges (MIC90s) of DS-2969b against C. difficile and S. aureus were 0.03–0.125 (0.125) μg/ml and 0.125–1 (0.5) μg/ml, respectively. DS-2969b showed the greatest activity of the agents tested. There was no difference in MICs of DS-2969b among different ribotypes.

Oral vancomycin is used to treat Clostridioides (Clostridium) difficile infection. Several different preparations are available including reconstituted IV solutions, vancomycin capsules, and grape flavored vancomycin oral solution kit (CutisPharma). The shelf life for IV after reconstitution varies between 7 and 14 days under refrigeration, and a standard 30 days for vancomycin oral solution kit (CutisPharma). The impact of storage on the in vitro potency was determined in 3 different vancomycin preparations by measuring MICs for 100 strains of C. difficile and 25 strains of Staphylococcus aureus, at T0, 14, 30, and 60 days, stored at ambient (RT) and refrigerated (2–5 °C) temperatures. All vancomycin preparations showed potency over a period of 60 days regardless of storage conditions. However, the capsule preparation showed mold after 60 days at room temperature, but unlike vancomycin oral solution kit, which retained a clear appearance, the IV and capsule preps showed evidence of crystallization.

From Monoclonal Antibodies for C. difficile Therapy II, no participants (n = 0/69) with a sustained clinical cure through 12 weeks following bezlotoxumab infusion experienced recurrent Clostridioides difficile infection (rCDI) after 9 months (versus actoxumab + bezlotoxumab, n = 2/65; versus placebo, n = 1/34). Bezlotoxumab’s efficacy appears to be due to prevention rather than delayed onset of rCDI.Clinical Trials Registration. NCT01513239.

We compared the eSwab system to a swab with an anaerobic transport semisolid agar system for their capacities to maintain the viability of 20 species of fastidious anaerobes inoculated on the bench and held at ambient or refrigerator temperature for 24 or 48 h. On average, both systems maintained similar viabilities among analogous groups of organisms at both temperatures, although there were quantitative differences among some species.

Clostridium difficile -associated diarrhea has been associated with disruption of the normal intestinal microbiota, particularly the Bacteroides fragilis group and Prevotella species. Surotomycin is a bactericidal cyclic lipopeptide in development for treatment of Clostridium difficile -associated diarrhea that has selective and potent activity against C. difficile and other Gram-positive bacteria and a minimal impact on intestinal Gram-negative organisms. The impacts of ascending doses of surotomycin on major organism groups in the gut microbiota of healthy volunteers were evaluated during a randomized, double-blind, placebo-controlled, multiple-dose phase 1 study. Thirty volunteers were randomized into 3 cohorts, using a 4:1 ratio, to receive 250 mg, 500 mg, or 1,000 mg of surotomycin, or placebo, twice daily for 14 days. Stool samples collected at baseline (days 0 and 1) and at the end of treatment (days 13 to 15) were cultured quantitatively. The B. fragilis group, the Bacteroides / Prevotella group, and Enterobacteriaceae were also quantified by quantitative real-time PCR. Baseline and end-of-treatment stool samples showed 1- to 2-log 10 CFU/g reductions in total bacterial counts for most volunteers. Various decreases in clostridial, Lactobacillus-Bifidobacterium group, and enterococcus-streptococcus group counts occurred while patients were receiving surotomycin, whereas the enterobacteria and the B. fragilis group persisted at the end of treatment. There was no change in enterococcus MICs of surotomycin, nor was vancomycin-resistant Enterococcus detected after exposure. Surotomycin at doses of up to 1,000 mg twice daily had only modest disruptive effects on the gut microbiota. The potential sparing of the gut microbiota by surotomycin may decrease the risk of disease recurrence.

Omadacycline was tested against 125 isolates recovered from infected cat and dog bites in humans. Its activity was similar to that of other compounds in the tetracycline class, and it was active against strains exhibiting tetracycline resistance. Against anaerobic isolates, resistance to tetracyclines was more prominent and omadacycline was the most active of the group. All isolates had omadacycline MICs of Eikenella corrodens , which showed reduced susceptibility to the entire tetracycline group.

The prevalence of C. difficile infection (CDI) and severe CDI are influenced by the prevalence of specific C. difficile strains, which are themselves influenced by antimicrobial susceptibility determinants as well as antimicrobial usage patterns. Restriction endonuclease analysis (REA) typing and antimicrobial susceptibility testing were used to characterize 1808 C. difficile isolates obtained from patients enrolled in four multicenter, multi-country, randomized CDI treatment trials conducted between 2006 and 2009 and between 2012 and 2015. By 2015, the epidemic REA group BI strain (RT027) had decreased in prevalence in North America (US: 43%-18%, Canada: 39%-24%, P 0.001), but rates of moxifloxacin resistance remained high. In contrast, REA group Y (RT014/020) and DH (RT106) strains, both of which had low rates of moxifloxacin resistance, increased in prevalence (Y strain - US: 6%-17%, Canada: 11%-23%, P 0.001; DH strain - US: 1%-11%, Canada: 0%-8%, P 0.0001). In Europe, the BI strain (RT027) was highly prevalent in Eastern European countries in 2015, but was unchanged in other parts of Europe. As in North America, the Y strain (RT014/020) was prevalent in both time periods, but the DH strain was rarely identified. Continued international molecular surveillance of C. difficile will be important to track prevalence of known epidemic strains and detect emergence of new strains of potential epidemiologic significance.

Relebactam is an important beta-lactamase inhibitor for certain aerobic organisms, but alone it has no antianaerobic activity, with most anaerobes having MICs of ≥32 μg/ml with the exception of a very few strains. There was no enhancement or antagonism of imipenem activity with the addition of relebactam, including activity against imipenem-resistant strains. The relebactam-imipenem combination had excellent overall activity against the anaerobes tested.

Omadacycline was tested against 125 isolates recovered from infected cat and dog bites in humans. Its activity was similar to that of other compounds in the tetracycline class, and it was active against strains exhibiting tetracycline resistance. Against anaerobic isolates, resistance to tetracyclines was more prominent and omadacycline was the most active of the group. All isolates had omadacycline MICs of

Pexiganan, a cationic peptide, exhibited a broad range of anti-anaerobic antimicrobial activity. The MIC 90 s of studied isolates were as follows: Bacteroides fragilis , 16 μg/ml; other B. fragilis group spp., 4 μg/ml; Prevotella and Fusobacterium spp., 32 μg/ml; Porphyromonas spp., 64 μg/ml; Propionibacterium acnes , 4 μg/ml; Eggerthella lenta and Peptostreptococcus anaerobius , 32 μg/ml; other Gram-positive rods and cocci, 4 μg/ml; Clostridium perfringens , 128 μg/ml; and other clostridia, 256 μg/ml. Pexiganan cream shows potential as adjunctive therapy for skin and skin structure infections (SSSIs) involving anaerobes.

Animal bite wounds affect more than 5 million Americans annually, resulting in 300,000 emergency department visits, 10,000 hospitalizations, and an untold number of physician office visits. Various forms of topical therapy are empirically self-employed by many patients prior to seeking medical attention. Pexiganan, a 22-amino-acid synthetic cationic analogue of the peptide magainin II, acts by selectively damaging bacterial cell membranes. We determined the MICs for pexiganan and other antimicrobial agents often used for treatment of bite wounds. Most isolates were from U.S. patients, and ∼10% were from European and Canadian patients. The comparator antimicrobials studied were penicillin, amoxicillin-clavulanate, piperacillin-tazobactam, meropenem, clindamycin, doxycycline, moxifloxacin, ceftriaxone, linezolid, and metronidazole. The MIC 90 s of pexiganan were 32 μg/ml (against Pasteurella multocida subsp. multocida ), 16 μg/ml ( P. multocida subsp. septica , Pasteurella canis , and Pasteurella dagmatis ), 8 μg/ml ( Pasteurella stomatis ), 8 μg/ml ( Eikenella corrodens ), 2 μg/ml ( Neisseria weaveri , Neisseria zoodegmatis , and Moraxella canis-Moraxella lacunata group), 16 μg/ml ( Bergeyella zoohelcum ), 64 μg/ml ( Bacteroides pyogenes ), 4 μg/ml ( Fusobacterium russii ), 32 μg/ml ( Fusobacterium canifelinum ), and 64 μg/ml ( Prevotella heparinolytica ). The concentration of pexiganan in the cream used was 8,000 μg/ml, more than 60 to 100 times the highest MIC obtained. Pexiganan exhibited a broad range of antimicrobial activity, showing potential for treating animal bite infections. A clinical trial seems warranted.

We determined the comparative activity of SMT19969 (SMT) against 162 strains representing 35 well-characterized Clostridium species in clusters I to XIX and 13 Clostridium species that had no 16S rRNA match. SMT MICs ranged from 0.06 to >512 μg/ml and were not species related. SMT might have less impact on normal gut microbiota than other Clostridium difficile infection (CDI) antimicrobials.

The comparative in vitro activity of SMT19969, a novel, narrow-spectrum, nonabsorbable agent, was studied against 50 ribotype-defined Clostridium difficile strains, 174 Gram-positive and 136 Gram-negative intestinal anaerobes, and 40 Gram-positive aerobes. SMT19969 was one dilution more active against C. difficile isolates (MIC range, 0.125 to 0.5 μg/ml; MIC 90 , 0.25 μg/ml), including ribotype 027 strains, than fidaxomicin (range, 0.06 to 1 μg/ml; MIC 90 , 0.5 μg/ml) and two to six dilutions lower than either vancomycin or metronidazole. SMT19969 and fidaxomicin were generally less active against Gram-negative anaerobes, especially the Bacteroides fragilis group species, than vancomycin and metronidazole, suggesting that SMT19969 has a lesser impact on the normal intestinal microbiota that maintain colonization resistance. SMT19969 showed limited activity against other Gram-positive anaerobes, including Bifidobacteria species, Eggerthella lenta , Finegoldia magna , and Peptostreptococcus anaerobius , with MIC 90 s of >512, >512, 64, and 64 μg/ml, respectively. Clostridium species showed various levels of susceptibility, with C. innocuum being susceptible (MIC 90 , 1 μg/ml) and C. ramosum and C. perfringens being nonsusceptible (MIC 90 , >512 μg/ml). Activity against Lactobacillus spp. (range, 0.06 to >512 μg/ml; MIC 90 , >512 μg/ml) was comparable to that of fidaxomicin and varied by species and strain. Gram-positive aerobic cocci ( Staphylococcus aureus , Enterococcus faecalis , E. faecium , and streptococci) showed high SMT19969 MIC 90 values (128 to >512 μg/ml).

Biapenem is a carbapenem being developed in combination with RPX7009, a new inhibitor of serine β-lactamases. Biapenem was tested alone and in combination with fixed concentrations of RPX7009 by agar dilution against 377 recent isolates of anaerobes. A separate panel of 27 isolates of Bacteroides spp. with decreased susceptibility or resistance to imipenem was also tested. Comparator drugs included meropenem, piperacillin-tazobactam, ampicillin-sulbactam, cefoxitin, ceftazidime, metronidazole, clindamycin, and tigecycline plus imipenem, doripenem, and ertapenem for the 27 selected strains. For recent consecutive strains of Bacteroides species, the MIC 90 for biapenem-RPX7009 was 1 μg/ml, with a MIC 90 of 4 μg/ml for meropenem. Other Bacteroides fragilis group species showed a MIC 90 of 0.5 μg/ml for both agents. The MIC 90 s for biapenem-RPX7009 were 0.25 μg/ml for Prevotella spp., 0.125 μg/ml for Fusobacterium nucleatum and Fusobacterium necrophorum , 2 μg/ml for Fusobacterium mortiferum , 0.5 μg/ml for Fusobacterium varium , ≤0.5 μg/ml for Gram-positive cocci and rods, and 0.03 to 8 μg/ml for clostridia. Against 5 B. fragilis strains harboring a known metallo-beta-lactamase, biapenem-RPX7009 MICs were comparable to those of other carbapenems (≥32 μg/ml). Against Bacteroides strains with an imipenem MIC of 2 μg/ml, biapenem-RPX7009 had MICs of 0.5 to 2 μg/ml, with MICs of 0.5 to 32 μg/ml for meropenem, doripenem, and ertapenem. For strains with an imipenem MIC of 4 μg/ml, the MICs for biapenem-RPX7009 were 4 to 16 μg/ml, with MICs of 8 to >32 μg/ml for meropenem, doripenem, and ertapenem. The inhibitor RPX7009 had no antimicrobial activity when tested alone, and it showed little or no potentiation of biapenem versus anaerobes. Biapenem-RPX7009 showed activity comparable to that of imipenem and was superior to meropenem, doripenem, and ertapenem against imipenem-nonsusceptible Bacteroides spp.

It has been speculated that the oral flora of the Komodo dragon (Varanus komodoensis) exerts a lethal effect on its prey; yet, scant information about their specific oral flora bacteriology, especially anaerobes, exists. Consequently, the aerobic and anaerobic oral bacteriology of 16 captive Komodo dragons (10 adults and six neonates), aged 2-17 yr for adults and 7-10 days for neonates, from three U.S. zoos were studied. Saliva and gingival samples were collected by zoo personnel, inoculated into anaerobic transport media, and delivered by courier to a reference laboratory. Samples were cultured for aerobes and anaerobes. Strains were identified by standard methods and 16S rRNA gene sequencing when required. The oral flora consisted of 39 aerobic and 21 anaerobic species, with some variation by zoo. Adult dragons grew 128 isolates, including 37 aerobic gram-negative rods (one to eight per specimen), especially Enterobacteriaceae; 50 aerobic gram-positive bacteria (two to nine per specimen), especially Staphylococcus sciuri and Enterococcusfaecalis, present in eight of 10 and nine of 10 dragons, respectively; and 41 anaerobes (one to six per specimen), especially clostridia. All hatchlings grew aerobes but none grew anaerobes. No virulent species were isolated. As with other carnivores, captive Komodo oral flora is simply reflective of the gut and skin flora of their recent meals and environment and is unlikely to cause rapid fatal infection.

Study objective The incidence of Clostridium difficile infection has increased and has been observed among persons from the community who have not been exposed to antibiotics or health care settings. Our aims are to determine prevalence of C difficile infection among emergency department (ED) patients with diarrhea and the prevalence among patients without traditional risk factors. Methods We conducted a prospective observational study of patients aged 2 years or older with diarrhea (≥3 episodes/24 hours) and no vomiting in 10 US EDs (2010 to 2013). We confirmed C difficile infection by positive stool culture result and toxin assay. C difficile infection risk factors were antibiotic use or overnight health care stay in the previous 3 months or previous C difficile infection. We typed strains with pulsed-field gel electrophoresis. Results Of 422 participants, median age was 46 years (range 2 to 94 years), with median illness duration of 3.0 days and 43.4% having greater than or equal to 10 episodes of diarrhea during the previous 24 hours. At least one risk factor for C difficile infection was present in 40.8% of participants; 25.9% were receiving antibiotics, 26.9% had health care stay within the previous 3 months, and 3.3% had previous C difficile infection. Forty-three participants (10.2%) had C difficile infection; among these, 24 (55.8%) received antibiotics and 19 (44.2%) had health care exposure; 17 of 43 (39.5%) lacked any risk factor. Among participants without risk factors, C difficile infection prevalence was 6.9%. The most commonly identified North American pulsed-field gel electrophoresis (NAP) strains were NAP type 1 (23.3%) and NAP type 4 (16.3%). Conclusion Among mostly adults presenting to US EDs with diarrhea and no vomiting, C difficile infection accounted for approximately 10%. More than one third of patients with C difficile infection lacked traditional risk factors for the disease. Among participants without traditional risk factors, prevalence of C difficile infection was approximately 7%.

Because Bacteroides fragilis has the ability to develop mechanisms of resistance to almost all antibiotics, we studied the comparative in vitro activity of tedizolid against 124 Bacteroides group species clinical isolates, including carbapenem, metronidazole and piperacillin-tazobactam resistant strains. Tedizolid had an MIC90 of 2 μg/ml (range, 0.5–4 μg/ml) and was 1–4 times more active than linezolid that had an MIC90 of 8 μg/ml (range, 2–16 μg/ml). It was also active (MICs 0.5–2 μg/ml) against the 27 ertapenem, 2 metronidazole and 12 piperacillin-tazobactam resistant strains tested. This suggests that tedizolid may be useful treating infections, including bacteremias, due to resistant B. fragilis group species, as well as, mixed skin and soft tissue infections such as diabetic foot infections caused by Gram-positive aerobes and B. fragilis group species.

The recent proposal by Lawson and Rainey (2015) to restrict the genus Clostridium to Clostridium butyricum and related species has ramifications for the members of the genera that fall outside this clade that should not be considered as Clostridium sensu stricto. One such organism of profound medical importance is Clostridioides difficile that is a major cause of hospital-acquired diarrhea and mortality in individuals. Based on 16S rRNA gene sequence analysis, the closest relative of Clostridium difficile is Clostridium mangenotii with a 94.7% similarity value and both are located within the family Peptostreptococcaceae that is phylogenetically far removed from C. butyricum and other members of Clostridium sensu stricto. Clostridium difficile is Clostridium mangenotii each produce abundant H2 gas when grown in PYG broth and also produce a range of straight and branched chain saturated and unsaturated fatty acids with C16:0 as a major product. The cell wall peptidoglycan contains meso-DAP as the diagnostic diamino acid. Based on phenotypic, chemotaxonomic and phylogenetic analyses, novel genus Clostridioides gen. nov. is proposed for Clostridium difficile as Clostridioides difficile gen. nov. comb. nov. and that Clostridium mangenotii be transferred to this genus as Clostridioides mangenotii comb. nov. The type species of Clostridioides is Clostridioides difficile.

Clostridium difficile infection (CDI) is the leading cause of infectious healthcare-associated diarrhoea. Recurrent CDI increases disease morbidity and mortality, posing a high burden to patients and a growing economic burden to the healthcare system. Thus, there exists a significant unmet and increasing medical need for new therapies for CDI. This review aims to provide a concise summary of CDI in general and a specific update on ridinilazole (formerly SMT19969), a novel antibacterial currently under development for the treatment of CDI. Owing to its highly targeted spectrum of activity and ability to spare the normal gut microbiota, ridinilazole provides significant advantages over metronidazole and vancomycin, the mainstay antibiotics for CDI. Ridinilazole is bactericidal against C. difficile and exhibits a prolonged post-antibiotic effect. Furthermore, treatment with ridinilazole results in decreased toxin production. A phase 1 trial demonstrated that oral ridinilazole is well tolerated and specifically targets clostridia whilst sparing other faecal bacteria. Phase 2 and 3 trials will hopefully further our understanding of the clinical utility of ridinilazole for the treatment of CDI.

More than 5 million Americans are bitten by animals, usually dogs, annually. Bite patients comprise ∼1% of all patients who visit emergency departments (300,000/year), and approximately 10,000 require hospitalization and intravenous antibiotics. Ceftaroline is the bioactive component of the prodrug ceftaroline fosamil, which is FDA approved for the treatment of acute bacterial skin and skin structure infections (ABSSSIs), including those containing methicillin-resistant Staphylococcus aureus (MRSA). There are no in vitro data about the activity of ceftaroline against Pasteurella multocida subsp. multocida and Pasteurella multocida subsp. septica , other Pasteurella spp., or other bite wound isolates. We therefore studied the in vitro activity of ceftaroline against 243 animal bite isolates. MICs were determined using the broth microdilution method according to CLSI guidelines. Comparator drugs included cefazolin, ceftriaxone, ertapenem, ampicillin-sulbactam, azithromycin, doxycycline, and sulfamethoxazole-trimethoprim (SMX-TMP). Ceftaroline was the most active agent against all 5 Pasteurella species, including P. multocida subsp. multocida and P. multocida subsp. septica , with a maximum MIC of ≤0.008 μg/ml; more active than ceftriaxone and ertapenem (MIC 90 s, ≤0.015 μg/ml); and more active than cefazolin (MIC 90 , 0.5 μg/ml) doxycycline (MIC 90 , 0.125 μg/ml), azithromycin (MIC 90 , 0.5 μg/ml), ampicillin-sulbactam (MIC 90 , 0.125 μg/ml), and SMX-TMP (MIC 90 , 0.125 μg/ml). Ceftaroline was also very active against all S. aureus isolates (MIC 90 , 0.125 μg/ml) and other Staphylococcus and Streptococcus species, with a maximum MIC of 0.125 μg/ml against all bite isolates tested. Ceftaroline has potential clinical utility against infections involving P. multocida , other Pasteurella species, and aerobic Gram-positive isolates, including S. aureus .

Clostridium difficile infection (CDI) causes moderate to severe disease, resulting in diarrhea and pseudomembranous colitis. CDI is difficult to treat due to production of inflammation-inducing toxins, resistance development, and high probability of recurrence. Only two antibiotics are approved for the treatment of CDI, and the pipeline for therapeutic agents contains few new drugs. MBX-500 is a hybrid antibacterial, composed of an anilinouracil DNA polymerase inhibitor linked to a fluoroquinolone DNA gyrase/topoisomerase inhibitor, with potential as a new therapeutic for CDI treatment. Since MBX-500 inhibits three bacterial targets, it has been previously shown to be minimally susceptible to resistance development. In the present study, the in vitro and in vivo efficacies of MBX-500 were explored against the Gram-positive anaerobe, C. difficile . MBX-500 displayed potency across nearly 50 isolates, including those of the fluoroquinolone-resistant, toxin-overproducing NAP1/027 ribotype, performing as well as comparator antibiotics vancomycin and metronidazole. Furthermore, MBX-500 was a narrow-spectrum agent, displaying poor activity against many other gut anaerobes. MBX-500 was active in acute and recurrent infections in a toxigenic hamster model of CDI, exhibiting full protection against acute infections and prevention of recurrence in 70% of the animals. Hamsters treated with MBX-500 displayed significantly greater weight gain than did those treated with vancomycin. Finally, MBX-500 was efficacious in a murine model of CDI, again demonstrating a fully protective effect and permitting near-normal weight gain in the treated animals. These selective anti-CDI features support the further development of MBX 500 for the treatment of CDI.

Our study sought to compare the strain types of Clostridium difficile causing initial and recurrent episodes of C. difficile infection (CDI) in adult patients with a first episode of CDI or 1 prior episode of CDI within the previous 90 days. Strains originated from patients who had been entered into two phase 3 randomized clinical trials of fidaxomicin versus vancomycin. Isolates of C. difficile from the initial and recurrent episodes within 28 (±2) days of cure of CDI were compared using restriction endonuclease analysis (REA) typing. Paired isolates were available from 90 of 194 (46%) patients with recurrent CDI. Patients with isolates available were significantly younger (P = .008) and more likely to be from Canadian sites (P = .0001), compared with patients without isolates. In 75 of 90 subjects (83.3%), the identical REA type strain was identified at recurrence and the initial episode (putative relapse). Early recurrences (0–14 days after treatment completion) were relapses in 86.7% and a new strain (reinfection) in 13.3%. Later recurrences (15–31 days after treatment) were relapses in 76.7% and reinfections in 23.3%. Mean time (± standard deviation) to recurrence was 12.2 (±6.4) days for relapses and 14.7 (±6.8) days for reinfections (P = .177). The most common BI/NAP1/027 group and the previous US epidemic REA group J/NAP2/001 had a significantly higher combined rate of recurrence with the same strain (relapse), compared with the other REA groups (39 of 42 [93%] vs 36 of 48 [75%], respectively; P = .023). We found a higher than historic rate of recurrent CDI caused by the same isolate as the original episode, a finding that may be related to the relatively short observation period in this study and the high frequency of isolation of epidemic strains, such as groups BI and J, for which relapse rates may be higher than for other REA groups. Caution in generalizing these observations is required, because the patients studied were younger and more likely to be from Canadian sites than were patients with recurrence who did not provide isolates. Clinical Trials Registration. NCT00314951 and NCT00468728.

The in vitro activities of LFF571, a novel analog of GE2270A that inhibits bacterial growth by binding with high affinity for protein synthesis elongation factor Tu, fidaxomicin, and 10 other antimicrobial agents were determined against 50 strains of Clostridium difficile and 630 other anaerobic and aerobic organisms of intestinal origin. LFF571 possesses potent activity against C. difficile and most other Gram-positive anaerobes (MIC 90 , ≤0.25 μg/ml), with the exception of bifidobacteria and lactobacilli. The MIC 90 s for aerobes, including enterococci, Staphylococcus aureus (as well as methicillin-resistant S. aureus [MRSA] isolates), Streptococcus pyogenes , and other streptococci were 0.06, 0.125, 2, and 8 μg/ml, respectively. Comparatively, fidaxomicin showed variable activity against Gram-positive organisms: MIC 90 s against C. difficile , Clostridium perfringens , and Bifidobacterium spp. were 0.5, ≤0.015, and 0.125 μg/ml, respectively, but >32 μg/ml against Clostridium ramosum and Clostridium innocuum . MIC 90 for S. pyogenes and other streptococci was 16 and >32 μg/ml, respectively. LFF571 and fidaxomicin were generally less active against Gram-negative anaerobes.

Two groups of previously undescribed anaerobic, gram-positive cocci recovered from human clinical infections were characterized using phenotypic and molecular genotypic methods. Comparative genotypic analysis showed that the strains within each of these two groups were homogeneous within the group and that each group was unique within the genus Peptoniphilus. The first group is most closely related to Peptoniphilus ivorii and the second group to Peptoniphilus harei. Based on these findings we propose two novel species, Peptoniphilus coxii sp. nov. and Peptoniphilus tyrrelliae sp. nov. The type strains are P. coxii sp. nov., RMA 16757(T) (= JCM 16892(T) = CCUG 59622(T) = ATCC BAA-2106(T)) and P. tyrrelliae sp. nov., RMA 19911(T) (= JCM 16893(T) = CCUG 59621(T) = ATCC BAA-2105(T)).

TD-1792 is a multivalent glycopeptide-cephalosporin heterodimer antibiotic with potent activity against Gram-positive bacteria. We tested TD-1792 against 377 anaerobes and 34 strains of Corynebacterium species. Against nearly all Gram-positive strains, TD-1792 had an MIC 90 of 0.25 μg/ml and was typically 3 to 7 dilutions more active than vancomycin and daptomycin.

A 10-day course of oral fidaxomicin (200 mg twice a day [b.i.d.]), a potent new macrocyclic drug, was compared to vancomycin (125 mg four times a day [q.i.d.]) in 1,164 adults (1,105 in the modified intent-to-treat [mITT] population) with Clostridium difficile infection in two phase III randomized, double-blind trials at sites in North America and 7 European countries. Of 1,105 mITT patients, 792 (71.7%), including 719/999 (72.0%) in the per-protocol (PP) population, provided a C. difficile strain at baseline, of whom 356 received fidaxomicin with 330 cures (92.7%) and 363 received vancomycin with 329 cures (90.6%). The susceptibilities (MIC 90 ) of baseline isolates did not predict clinical cure, failure, or recurrence for fidaxomicin (MIC 90 , 0.25 μg/ml for both; range, ≤0.007 to 1 μg/ml), but there was a one-dilution difference in the MIC 90 (but not the MIC 50 ) for vancomycin (MIC 90 , 2 μg/ml [range, 0.25 to 8 μg/ml] for cure and 4.0 μg/ml [range, 0.5 to 4 μg/ml] for failures). A total of 65 (7.9%) “rifaximin-resistant” (MIC > 256 μg/ml) strains were isolated in both treatment groups on enrollment, which increased to 25% for failures at the end of therapy. No resistance to either fidaxomicin or vancomycin developed during treatment in either of the phase III studies, although a single strain isolated from a cured patient had an elevated fidaxomicin MIC of 16 μg/ml at the time of recurrence. All isolates were susceptible to ≤4 μg/ml of metronidazole. When analyzed by restriction endonuclease analysis (REA) type, 247/719 (34.4%) isolates were BI group isolates, and the MICs were generally higher for all four drugs tested (MIC 90 s: fidaxomicin, 0.5; vancomycin, 2.0; metronidazole, 2.0; and rifaximin, >256 μg/ml) than for the other REA types. There was no correlation between the MIC of a baseline clinical isolate and clinical outcome. MIC 90 s were generally low for fidaxomicin and vancomycin, but BI isolates had higher MICs than other REA group isolates.

NXL104, a novel β-lactamase inhibitor, was tested at a constant concentration of 4 μg/ml in combination with ceftazidime (CAZ), with and without added metronidazole, against 396 β-lactamase-producing strains of anaerobic bacteria. MIC 50 /MIC 90 values for Bacteroides fragilis and the B. fragilis group were 8/16 and 64/>128 μg/ml, respectively. Although CAZ-NXL104 had limited activity against most anaerobic strains, in combination with metronidazole it shows potential for treating mixed infections involving resistant Enterobacteriaceae and anaerobes.

Alistipes (previously Bacteroides) are strictly anaerobic gram-negative rods that resemble the Bacteroides fragilis group in that most species are bile-resistant and indole-positive; however, they are only weakly saccharolytic and most species produce light brown pigment only on laked rabbit blood agar. In this retrospective study, we re-identified 18 organisms previously identified phenotypically as "Bacteroides putredinis-like", but that did not produce pigment on routine media. The strains were identified with 16S rDNA sequencing and pigment production was evaluated on several different culture media. Only 12/18 strains had molecular identifications of Alistipes species, while the remaining strains phylogenetically resembled Butyricimonas and Odoribacter spp. Pigment production was not a reliable test for those Alistipes strains that are described as pigment producers.

Garenoxacin, a des-(F)6-quinolone, was tested using the agar dilution method against 536 anaerobic bacteria, composed of 408 unusual strains from various sources and 128 pelvic isolates. Only 33/408 (8%) unusual isolates and 6/128 (4.7%) pelvic isolates had garenoxacin MICs ≥ 4 μg/mL, and 18 and 3 (4.4% and 2.3% of the respective totals) had MICs ≥ 8 μg/mL. Less susceptible unusual isolates included 7/15 Veillonella sp. from various clinical sources, 6/14 Fusobacterium varium from predominantly abdominal infections, 5/5 F. russii (cat bites), and 6/9 Actinomyces israelii. Overall, garenoxacin showed good activity against the isolates studied and has potential utility in mixed aerobic/anaerobic infections.

Due to a high rate of relapse, osteomyelitis remains difficult to treat, requiring prolonged parenteral therapy. MICs for 41 consecutive Staphylococcus species recovered from patients with osteomyelitis were determined for dalbavancin, daptomycin, doxycycline, levofloxacin, linezolid, vancomycin, trimethoprim-sulfamethoxazole, rifampin, and vancomycin. Strains of vancomycin-intermediate Staphylococcus aureus (VISA) and heteroresistant VISA were included for additional comparison. Except for rifampin, dalbavancin was the most active agent tested. Dalbavancin is given once a week, making treatment of infections such as osteomyelitis potentially more convenient and thus could help reduce the rate of hospitalizations and outpatient costs.

Background Recurrence of CDI (rCDI) is associated with perturbation of the gut microbiome during treatment with vancomycin (VAN) or metronidazole (MTZ). RDZ is a novel, targeted spectrum antibacterial under investigation to treat CDI and reduce rCDI. Here correlation of in vitro spectrum of activity with preservation of the human gut microbiome and clinical outcomes is presented. Methods Susceptibility testing was to CLSI standards with VAN, MTZ, and fidaxomicin (FDX) comparators. The Phase 2 clinical trial was a double-blind, randomized study of 100 patients assigned 1:1 to 10 days RDZ 200 mg BID or VAN 125 mg QID treatment. Primary endpoint was sustained clinical response (SCR), defined as cure at end of therapy (EOT), and no rCDI for the next 30 days. Relative effects of RDZ and VAN on the gut microbiome were examined by sequencing 16S rDNA amplicons from stool collected at baseline, days 5, 10, 25, and end of study. Bioinformatic analyses were performed in QIIME. Results RDZ C. difficile (N = 50) MIC range was 0.125–0.25 μg/mL. Clostridium spp. showed varied RDZ susceptibility; C. innocuum MIC90 1 μg/mL, C. ramosum and C. perfringens MIC90 >512 μg/mL. VAN showed potent to moderate growth inhibition of all Clostridium spp. (MIC range 1–16 µg/mL). Limited RDZ activity was observed for Gram-positive anaerobes, including Bifidobacteria, Eggerthella, Finegoldia, and Peptostreptococcus (MIC90 >512, >512, 64, and 64 μg/mL) compared with VAN (MIC90 1, 4, 0.5, and 0.5 μg/mL). Bacteroides fragilis MIC90 for RDZ and VAN were >512 and 64 µg/mL, respectively. These in vitro data correlate closely with human microbiome profiles. RDZ reduced C. difficile to below detection with other reductions in abundancy observed in only 2 families from the Clostridia. VAN at EOT resulted in significant losses, often below detection, in 4 Firmicutes families, Actinobacteria, and Bacteroidetes and a 25-fold increase in Proteobacteria abundance. The preservation of the microbiome by RDZ likely accounted for reduced rCDI compared with VAN with RDZ shown to be superior on SCR to VAN with rates of 66.7% and 42.4%, respectively (pre-specified 90% CI 3.1, 39.1). Conclusion These data demonstrate strong translation of in vitro spectrum to human gut microbiome preservation during therapy and support further clinical development of RDZ. Disclosures R. Vickers, Summit Therapeutics: Employee, Salary and Stock options. E. J. C. Goldstein, Summit Therapeutics: Grant Investigator and Scientific Advisor, Consulting fee and Grant recipient. D. Citron, Summit Therapeutics: Grant Investigator, Research grant. D. Snydman, Summit Therapeutics: Grant Investigator, Grant recipient. C. M. Thorpe, Summit Therapeutics: Grant Investigator and Scientific Advisor, Consulting fee and Grant recipient. A. V. Kane, Summit Therapeutics: Grant Investigator, Grant recipient.

Strategies to reduce rates of Clostridium difficile infection (CDI) generally recommend isolation or cohorting of active cases and the reduced use of cephalosporin and quinolone antibiotics. Data supporting these recommendations come predominantly from the setting of epidemic disease caused by ribotype 027 strains. We introduced an initiative involving a restrictive antibiotic policy and a CDI-cohort ward at an acute, 820-bed teaching hospital where ribotype 027 strains account for only one quarter of all CDI cases. Antibiotic use and monthly CDI cases in the 12 months before and the 15 months after the initiative were compared using an interrupted time series analysis and segmented regression analysis. The initiative resulted in a reduced level of cephalosporin and quinolone use (22.0% and 38.7%, respectively, both p

We investigated vancomycin and daptomycin efficacy for Staphylococcus aureus isolates at our institution by testing 221 methicillin-sensitive and 299 methicillin-resistant isolates recovered from serious infections between 1979 and 2007 using a microdilution method. The MIC(90)'s for vancomycin remained constant at 2 microg/mL for methicillin-resistant S. aureus (MRSA) and methicillin-sensitive S. aureus (MSSA). For MSSA, the geometric mean vancomycin MICs remained at 1.1 microg/mL but varied from 1.1 to 1.7 for MRSA. Tolerance to vancomycin was seen in 6.5% of MRSA and 10.5% of MSSA. Daptomycin MIC(90)'s remained at < or =1 microg/mL, and the daptomycin concentration at which 90% of the strains were killed (MBC(90)) remained at 2 microg/ml. Over 29 years, no trend was detected in vancomycin or daptomycin susceptibilities. Daptomycin had excellent inhibitory and bactericidal activities against all strains throughout the years. Although vancomycin's inhibitory activity was consistent over time, vancomycin-tolerant strains whose presence was not predicted by their MIC were found.

Studies have demonstrated that thickened mucous layers in the lungs of cystic fibrosis (CF) patients contain areas of low oxygen tension. These microaerophilic environments may reduce the activity of aerosol antibiotics used in the management of chronic infection in CF. The aim of this study was to compare the MICs of levofloxacin, tobramycin, amikacin, and aztreonam against Pseudomonas aeruginosa under reference and anaerobic conditions and evaluate the in vitro pharmacodynamics of levofloxacin under aerobic and hypoxic testing conditions. The MICs for 114 isolates of P. aeruginosa from CF patients were determined in cation-adjusted Mueller Hinton broth alone or supplemented with 1% potassium nitrate for anaerobic testing. Levofloxacin time-kill curves were performed under aerobic and hypoxic conditions using strains of P. aeruginosa with elevated efflux pump overexpression and/or target mutations. The MICs of nonmucoid or mucoid P. aeruginosa isolates to levofloxacin incubated under aerobic and anaerobic conditions were similar. In contrast, anaerobic incubation resulted in higher MICs for tobramycin, amikacin, and aztreonam among nonmucoid or mucoid isolates, with > or =4-fold increase in MICs for over 40% of the isolates. Time-kill curves performed in aerobic and hypoxic environments with levofloxacin concentrations attained in CF sputum demonstrated similar activity, approaching a maximum bactericidal effect within 10 min of exposure. Together, these results indicate that the activity of some antibiotics against P. aeruginosa is significantly reduced under conditions relevant to the CF lung environment. In contrast, levofloxacin maintains activity against P. aeruginosa under anaerobic or hypoxic conditions similar to those found in CF microaerophilic environments.

Fusobacterium nucleatum is a Gram-negative anaerobic rod found in dental plaque biofilms, and is an opportunistic pathogen implicated in periodontitis as well as a wide range of systemic abscesses and infections. Genomic analyses of F. nucleatum indicate considerable genetic diversity and a prominent role for horizontal gene transfer in the evolution of the species. Several plasmids isolated from F. nucleatum, including pFN1, harbor relaxase gene homologues that may function in plasmid mobilization. In this investigation we examined the RP4-mediated mobilization properties of pFN1 and the prevalence of pFN1-related sequences in a panel of F. nucleatum clinical isolates. The fusobacterial plasmid pFN1 was mobilized by RP4 at a high frequency. Deletion analyses were used to delineate the core mobilon of pFN1, which consisted of the relaxase gene (rlx), an upstream open reading frame ORF4 and a region of DNA upstream of ORF4 with potential nic sites. To examine the prevalence of pFN1 in a panel of clinical isolates, total DNA isolated from the strains was hybridized with pFN1 replication (repA) and rlx gene probes. DNA from strains harboring plasmids known to be homologous to pFN1 hybridized with both the repA and rlx probes. Five additional strains were rlx-positive but repA-negative, indicating a greater prevalence of rlx-related genes in comparison with repA-related genes. Plasmid or plasmid-related sequences were identified in 11.5% of the strains examined. These findings demonstrate mobilization properties of a fusobacterial plasmid that may be important in horizontal gene transfer.

After ertapenem was added to the formulary of a 344-bed community teaching hospital, we retrospectively studied its effect on antimicrobial utilization and on the in vitro susceptibility of various antimicrobial agents against Pseudomonas aeruginosa . Three study periods were defined as preintroduction (months 1 to 9), postintroduction but before the autosubstitution of ertapenem for ampicillin-sulbactam (months 10 to 18), and after the policy of autosubstitution (months 19 to 48) was initiated. Ertapenem usage rose slowly from introduction to a range of 36 to 48 defined daily doses/1,000 patient days (DDD) with a resultant decrease in ampicillin-sulbactam usage due to autosubstitution. Imipenem usage peaked 6 months after the introduction of ertapenem and started to decline coincidently with the increased use of ertapenem. During the second period, imipenem usage decreased (slope = −1.28; P = 0.002). Prior to the introduction of ertapenem, the susceptibility of P. aeruginosa to imipenem increased from 61 to 81% at month 7 but then decreased slightly to 67% at month 9. After the introduction of ertapenem, susceptibility continued to increase; the increasing trend was significant (slope = 1.74; P < 0.001). In the third period, the median susceptibility (interquartile range) was 88% (82 to 95%). This change appeared related to decreased imipenem usage. For every unit decrease in the monthly DDD of imipenem, there was an increase of 0.38% ( P = 0.008) in the susceptibility of P. aeruginosa to imipenem in the same month. Ertapenem was effective in our antimicrobial stewardship program and may have helped improve the P. aeruginosa antimicrobial susceptibility to imipenem by decreasing the unnecessary usage and selective pressure of antipseudomonal agents.

A randomized study comparing single-dose cefotetan and ertapenem prophylaxis for elective colorectal surgery in 1,002 patients found ertapenem to be significantly more effective (p0.001). Failures of prophylaxis were thought to involve organisms resistant to both antimicrobial agents, isolated most often from deep or superficial incision sites.Further testing and analysis of the microbial data was performed. Susceptibility results were correlated with the clinical outcomes reported previously.Of the 216 aerobes tested, 62.6% were resistant to cefotetan and 44% to ertapenem. Enterococci and methicillin-resistant Staphylococcus epidermidis were the aerobes recovered most frequently, and Bacteroides thetaiotaomicron, Clostridium innocuum, and Eubacterium lentum were the most frequent anaerobes. Enterococcus faecalis usually was associated in mixed culture with Bacteroides fragilis group species. Approximately one-half of the 158 anaerobes (50.7%), including all the species above, were resistant to cefotetan; most of these (61.4%) came from superficial incision sites. Only one anaerobe (Desulfovibrio fairfieldensis), found in a superficial incisional infection, was resistant to ertapenem, and no ertapenem-resistant enteric bacteria were recovered. In vitro resistance was associated with therapeutic failure.The in vitro activity of ertapenem was superior to that of cefotetan against all anaerobic and many aerobic bacteria isolated from postoperative cultures of patients who failed prophylaxis with these agents. Our findings help to elucidate the results of the clinical trial.

Antimicrobial susceptibility testing of anaerobic isolates was conducted at four independent sites from 2010 to 2012 and compared to results from three sites during the period of 2007–2009. This data comparison shows significant changes in antimicrobial resistance in some anaerobic groups. Therefore, we continue to recommend institutions regularly perform susceptibility testing when anaerobes are cultured from pertinent sites. Annual generation of an institutional-specific antibiogram is recommended for tracking of resistance trends over time.