In vitro identification of underutilized ß-lactam combinations against methicillin-resistant Staphylococcus aureus bacteremia isolates.

Methicillin-resistant Staphylococcus aureus (MRSA) bacteremia is a serious clinical challenge with high mortality rates. Antibiotic combination therapy is currently used in cases of persistent infection; however, the limited development of new antibiotics will likely increase the need for combination therapy, and better methods are needed for identifying effective combinations for treating persistent bacteremia. To identify pairwise combinations with the most consistent potential for benefit compared to monotherapy with a primary anti-MRSA agent, we conducted a systematic study with an in vitro high-throughput methodology. We tested daptomycin and vancomycin each in combination with gentamicin, rifampicin, cefazolin, and oxacillin, and ceftaroline with daptomycin, gentamicin, and rifampicin. Combining cefazolin with daptomycin lowered the daptomycin concentration required to reach 95% growth inhibition (IC95) for all isolates tested and lowered daptomycin IC95 below the sensitivity breakpoint for five out of six isolates that had daptomycin minimum inhibitory concentrations at or above the sensitivity breakpoint. Similarly, vancomycin IC95s were decreased when vancomycin was combined with cefazolin for 86.7% of the isolates tested. This was a higher percentage than was achieved by adding any other secondary antibiotic to vancomycin. Adding rifampicin to daptomycin or vancomycin did not always reduce IC95s and failed to produce synergistic interaction in any of the isolates tested; the addition of rifampicin to ceftaroline was frequently synergistic and always lowered the amount of ceftaroline required to reach the IC95. These analyses rationalize further in vivo evaluation of three drug pairs for MRSA bacteremia: daptomycin+cefazolin, vancomycin+cefazolin, and ceftaroline+rifampicin.IMPORTANCEBloodstream infections caused by methicillin-resistant Staphylococcus aureus (MRSA) have a high mortality rate despite the availability of vancomycin, daptomycin, and newer antibiotics including ceftaroline. With the slow output of the antibiotic pipeline and the serious clinical challenge posed by persistent MRSA infections, better strategies for utilizing combination therapy are becoming increasingly necessary. We demonstrated the value of a systematic high-throughput approach, adapted from prior work testing antibiotic combinations against tuberculosis and other mycobacteria, by using this approach to test antibiotic pairs against a panel of MRSA isolates with diverse patterns of antibiotic susceptibility. We identified three antibiotic pairs-daptomycin+cefazolin, vancomycin+cefazolin, and ceftaroline+rifampicin-where the addition of the second antibiotic improved the potency of the first antibiotic across all or most isolates tested. Our results indicate that these pairs warrant further evaluation in the clinical setting.

The clinical effectiveness of Fidaxomicin compared to Vancomycin in the treatment of Clostridioides difficile infection, a single center real-world experience.

BACKGROUND: The use of fidaxomicin is recommended as first line therapy for all patients with Clostridioides difficile infection (CDI). However, real-world studies have shown conflicting evidence of superiority. METHODS: We conducted a retrospective single center study of patients diagnosed with CDI between 2011-2021. A primary composite outcome of clinical failure, 30-day relapse or CDI-related death was used. A multivariable cause specific Cox proportional hazards model was used to evaluate fidaxomicin compared to vancomycin in preventing the composite outcome. A separate model was fit on a subset of patients with C. difficile ribotypes adjusting for ribotype. RESULTS: There were 598 patients included, of whom 84 received fidaxomicin. The primary outcome occurred in 8 (9.5%) in the fidaxomicin group compared to 111 (21.6%) in the vancomycin group. The adjusted multivariable model showed fidaxomicin was associated with 63% reduction in the risk of the composite outcome compared to vancomycin (HR = 0.37, 95% CI 0.17-0.80). In the 337 patients with ribotype data after adjusting for ribotype 027, the results showing superiority of fidaxomicin were maintained (HR = 0.19, 95% CI 0.05-0.77). CONCLUSION: In the treatment of CDI, we showed that real-world use of fidaxomicin is associated with lower risk of a composite endpoint of treatment failure.

Impact of antimicrobial use in dogs on antimicrobial resistance and shared flora with human owners.

Transmission of bacteria between animals and humans in domestic households is increasingly recognized. We evaluated the presence of antimicrobial-resistant fecal bacteria in 8 dog-owner-dog pairs before and after the dog received amoxicillin-clavulanate. The study identified shared flora in the humans and dogs that were affected by antimicrobial administration.

Antimicrobial susceptibility and ribotypes of Clostridium difficile isolates from a Phase 2 clinical trial of ridinilazole (SMT19969) and vancomycin.

Objectives: We evaluated the antimicrobial susceptibility and ribotypes of Clostridium difficile isolates from participants in a Phase 2 study of ridinilazole, a novel targeted-spectrum agent for treatment of C. difficile infection. Methods: Participants received ridinilazole (200 mg twice daily) or vancomycin (125 mg four times daily) for 10 days (ClinicalTrials.gov: NCT02092935). The MICs of ridinilazole and comparators for C. difficile isolates from stool samples were determined by agar dilution. Toxin gene profiling was performed by multiplex PCR and ribotype identification by capillary electrophoresis. Results: Eighty-nine isolates were recovered from 88/100 participants (one participant had two strains at baseline). The median colony count (cfu/g stool) was 1.9 × 104 (range: 2.5 × 102-7.0 × 106). Twelve participants (three received ridinilazole and nine received vancomycin) experienced recurrence, confirmed by immunoassays for free toxin in stool samples. The ribotype of eight out of nine isolates obtained at recurrence matched those of the initial isolates. All isolates, including those obtained at recurrence, were susceptible to ridinilazole within the expected range [median (range) MIC: 0.12 (0.06-0.5) mg/L]. The median (range) vancomycin MIC was 1 (0.5-4.0) mg/L. At baseline, 13.6% and 13.3% of samples in the ridinilazole and vancomycin groups were positive for VRE, increasing to 23.7% and 29.7% by day 40, respectively. Common ribotypes included 014-20 (14 isolates), 027 (13), 106 (7), 002 (7), 078-126 (4), 001 (4), 087 (3) and 198 (3). Toxin gene profiling of nearly all baseline isolates (98.9%) revealed a binary toxin gene (cdtA/cdtB) prevalence of 35%. Conclusions: Ridinilazole potently inhibited recovered C. difficile isolates. Recurrence was not associated with altered susceptibility.

A repeat offender: Recurrent extraintestinal Clostridium difficile infection following fecal microbiota transplantation.

Extraintestinal infection with Clostridium difficile has been reported but remains uncommon. Treatment of this unusual complication is complex given the limitations of current therapeutic options. Here we report a novel case of recurrent extraintestinal C. difficile infection that occurred following fecal microbiota transplantation. Using whole genome sequencing, we confirmed recrudescence rather than reinfection was responsible. The patient ultimately responded to prolonged, targeted antimicrobial therapy informed by susceptibility testing.

Evaluation of the In Vitro Activity of Eravacycline against a Broad Spectrum of Recent Clinical Anaerobic Isolates.

The novel fluorocycline antibiotic eravacycline is in development for use in the treatment of serious infections caused by susceptible and multidrug-resistant (MDR) aerobic and anaerobic Gram-negative and Gram-positive pathogens. Eravacycline and 11 comparator antibiotics were tested against recent anaerobic clinical isolates, including MDR Bacteroides spp. and Clostridium difficile Eravacycline was potent in vitro against all the isolates tested, including strains with tetracycline-specific resistance determinants and MDR anaerobic pathogens resistant to carbapenems and/or ß-lactam-ß-lactamase inhibitor combinations.

In Vitro Evaluation of the Activity of Imipenem-Relebactam against 451 Recent Clinical Isolates of Bacteroides Group and Related Species.

We evaluated the in vitro activity of imipenem-relebactam (imipenem-MK7655) against 451 recent clinical isolates within the Bacteroides group and related species. Relebactam did not enhance or inhibit the activity of imipenem against Bacteroides fragilis or other Bacteroides species. No synergistic or antagonistic effect was observed. The MICs of imipenem-relebactam were equal to or within one dilution of the MICs of these isolates to imipenem.

Differences in the Molecular Epidemiology and Antibiotic Susceptibility of Clostridium difficile Isolates in Pediatric and Adult Patients.

The rising incidence of Clostridium difficile infections (CDIs) in adults is partly related to the global spread of fluoroquinolone-resistant strains, namely, BI/NAP1/027. Although CDIs are also increasingly diagnosed in children, BI/NAP1/027 is relatively uncommon in children. Little is known about the antibiotic susceptibility of pediatric CDI isolates. C. difficile was cultured from tcdB-positive stools collected from children diagnosed with CDI between December 2012 and December 2013 at an academic children's hospital. CDI isolates were grouped by restriction endonuclease analysis (REA). MICs were measured by agar dilution method for 7 antibiotics. Susceptibility breakpoints were based on guidelines from CLSI and/or the European Committee on Antimicrobial Susceptibility Testing (EUCAST). MICs and REA groupings of C. difficile isolates from 74 adult patients (29 isolates underwent REA) from a temporally and geographically similar adult cohort were compared to those of pediatric isolates. Among 122 pediatric and 74 adult isolates, respectively, the rates of resistance were as follows: metronidazole, 0% and 0%; vancomycin, 0% and 8% (P = 0.003); rifaximin, 1.6% and 6.7% (P = 0.11); clindamycin, 18.9% and 25.3% (P = 0.29); and moxifloxacin, 2.5% and 36% (P = <0.0001). Only 1 of 122 (0.8%) BI/NAP1/027 isolates was identified among the children, compared to 9 of 29 (31%) isolates identified among the adults (P = <0.0001). The 3 moxifloxacin-resistant pediatric isolates were of REA groups BI and CF and a nonspecific group. The 2 rifaximin-resistant pediatric isolates were of REA groups DH and Y. The 21 clindamycin-resistant pediatric isolates were distributed among 9 REA groups (groups A, CF, DH, G, L, M, and Y and 2 unique nonspecific REA groups). These data suggest that a diverse array of relatively antibiotic-susceptible C. difficile strains predominate in a cohort of children with CDI compared to adults.

Activity of ceftolozane-tazobactam against a broad spectrum of recent clinical anaerobic isolates.

We evaluated in vitro activity of ceftolozane-tazobactam (TOL-TAZ), formerly CXA-201, against recent clinical anaerobic isolates with emphasis on the Bacteroides fragilis group. Ceftolozane-tazobactam showed good activity against B. fragilis species and intermediate to limited activity against other species of Bacteroides. Ceftolozane-tazobactam showed very good activity against Prevotella spp., Fusobacterium spp., and Propionibacterium spp., varying activities against Gram-positive cocci, and limited activity against Clostridium spp.

In vitro activity of ceftaroline against a broad spectrum of recent clinical anaerobic isolates.

The in vitro activity of ceftaroline was compared with those of ceftriaxone, clindamycin, imipenem, metronidazole, moxifloxacin, tigecycline, and vancomycin against 514 clinical anaerobic isolates using Clinical and Laboratory Standards Institute (CLSI) standard methodology. Ceftaroline demonstrated good to excellent activity against Gram-positive anaerobic pathogens and limited activity against Gram-negative pathogens, particularly Bacteroides fragilis group isolates.

Candidaemia associated with decreased in vitro fluconazole susceptibility: is Candida speciation predictive of the susceptibility pattern?

BACKGROUND: Candidaemia is often treated with fluconazole in the absence of susceptibility testing. We examined factors associated with candidaemia caused by Candida isolates with reduced susceptibility to fluconazole. METHODS: We identified consecutive episodes of candidaemia at two hospitals from 2001 to 2007. Species identification followed CLSI methodology and fluconazole susceptibility was determined by Etest or broth microdilution. Susceptibility to fluconazole was defined as: full susceptibility (MIC < or = 8 mg/L); and reduced susceptibility (MIC > or = 32 mg/L). Complete resistance was defined as an MIC > 32 mg/L. RESULTS: Of 243 episodes of candidaemia, 190 (78%) were fully susceptible to fluconazole and 45 (19%) had reduced susceptibility (of which 27 were fully resistant). Of Candida krusei and Candida glabrata isolates, 100% and 51%, respectively, had reduced susceptibility. Despite the small proportion of Candida albicans (8%), Candida tropicalis (4%) and Candida parapsilosis (4%) with reduced fluconazole susceptibility, these species composed 36% of the reduced-susceptibility group and 48% of the fully resistant group. In multivariate analysis, independent factors associated with reduced fluconazole susceptibility included male sex [odds ratio (OR) 3.2, P < 0.01], chronic lung disease (OR 2.7, P = 0.01), the presence of a central vascular catheter (OR 4.0, P < 0.01) and prior exposure to antifungal agents (OR 2.2, P = 0.04). CONCLUSIONS: A significant proportion of candidaemia with reduced fluconazole susceptibility may be caused by C. albicans, C. tropicalis and C. parapsilosis, species usually considered fully susceptible to fluconazole. Thus, identification of these species may not be predictive of fluconazole susceptibility. Other factors that are associated with reduced fluconazole susceptibility may help clinicians choose adequate empirical anti-Candida therapy.

Lessons learned from the anaerobe survey: historical perspective and review of the most recent data (2005-2007).

BACKGROUND: The rationale and lessons learned through the evolution of the National Survey for the Susceptibility of Bacteroides fragilis Group from its initiation in 1981 through 2007 are reviewed here. The survey was conceived in 1980 to track emerging antimicrobial resistance in Bacteroides species. METHODS: Data from the last 11 years of the survey (1997-2007), including 6574 isolates from 13 medical centers, were analyzed for in vitro antimicrobial resistance to both frequently used and newly developed anti-anaerobic agents. The minimum inhibitory concentrations of the antibiotics were determined using agar dilution in accordance with Clinical and Laboratory Standards Institute recommendations. RESULTS: The analyses revealed that the carbapenems (imipenem, meropenem, ertapenem, and doripenem) and piperacillin-tazobactam were the most active agents against these pathogens, with resistance rates of 0.9%-2.3%. In the most recent 3 years of the survey (2005-2007), resistance to some agents was shown to depend on the species, such as ampicillin-sulbactam against Bacteroides distasonis (20.6%) and tigecycline against Bacteroides uniformis and Bacteroides eggerthii ( approximately 7%). Very high resistance rates (>50%) were noted for moxifloxacin and trovafloxacin, particularly against Bacteroides vulgatus. During that period of study, non-B. fragilis Bacteroides species had >40% resistance to clindamycin. Metronidazole-resistant Bacteroides strains were also first reported during that period. CONCLUSIONS: In summary, resistance to antibiotics was greater among non-B. fragilis Bacteroides species than among B. fragilis and was especially greater among species with a low frequency of isolation, such as Bacteroides caccae and B. uniformis. The emergence of resistance among the non-B. fragilis Bacteroides species underscores the need for speciation of B. fragilis group isolates and for clinicians to be aware of associations between species and drug resistance.

In vitro activities of doripenem, a new broad-spectrum carbapenem, against recently collected clinical anaerobic isolates, with emphasis on the Bacteroides fragilis group.

Doripenem was evaluated against 527 recent clinical isolates, i.e., 404 Bacteroides fragilis isolates and 123 gram-positive anaerobe isolates. Against B. fragilis, doripenem was as active as imipenem, meropenem, and piperacillin-tazobactam and more active than ertapenem or ampicillin-sulbactam. Doripenem was active against isolates resistant to ertapenem, ampicillin-sulbactam, cefoxitin, clindamycin, and moxifloxacin. All of the gram-positive isolates tested were susceptible to doripenem.

Evaluation of the in vitro activity of NVP-LMB415 against clinical anaerobic isolates with emphasis on the Bacteroides fragilis group.

OBJECTIVES: To compare the in vitro activity of NVP-LMB415 (formerly referred to as NVP-PDF 713) with that of other agents with anti-anaerobe activity against clinical anaerobic isolates, with emphasis on the Bacteroides fragilis group. METHODS: The MICs for 405 B. fragilis group and 102 Gram-positive anaerobic isolates were determined using NCCLS-recommended procedures. The activity of NVP-LMB415 was compared with that of cefoxitin, clindamycin, imipenem, garenoxacin, linezolid, moxifloxacin and tigecycline. Vancomycin was included in the evaluation of the Gram-positive organisms. RESULTS: NVP-LMB415 showed excellent in vitro activity against all the species of the B. fragilis group isolates (MIC range < or = 0.03-0.5 mg/L and MIC(90) 0.5 mg/L). NVP-LMB415 was active against B. fragilis group strains resistant to beta-lactams, quinolones or clindamycin, and the MICs were much lower than those of newer agents such as linezolid, tigecycline and garenoxacin. The MICs of NVP-LMB415 ( > or = 4 mg/L) for Clostridium species were higher than the MICs for other anaerobes. CONCLUSIONS: Given the frequency of isolation of anaerobic bacteria and their increasing resistance to all classes of antibiotics, NVP-LMB415 is an ideal agent for potential use against mixed infections caused by resistant anaerobic pathogens such as of B. fragilis and Gram-positive aerobic strains such as methicillin-resistant staphylococci, streptococci and enterococci.

Emergence of fluoroquinolone resistance among Bacteroides species.

BACKGROUND: Several newer generation fluoroquinolones have demonstrated good in vitro activity against Bacteroides species; particularly when first introduced. However, resistance of Bacteroides to quinolones appears to be increasing. MATERIALS AND METHODS: From 1994 to 2001, consecutive non-duplicated Bacteroides isolates from clinical specimens in 12 US hospitals were sent to the Tufts anaerobe laboratory for identification and susceptibility testing. NCCLS recommended methodology for testing was employed. Breakpoints of 8 mg/l for trovafloxacin and 4 mg/l for moxifloxacin were used to examine susceptibility trends. RESULTS: In total, 4434 isolates were analysed. The geometric mean MIC increased significantly for clinafloxacin, trovafloxacin and moxifloxacin. Resistance to trovafloxacin (breakpoint of 8 mg/l) and moxifloxacin (breakpoint of 4 mg/l) increased from 8% to 25% and from 30% to 43%, respectively. Increased resistance was observed for all Bacteroides species, for all sites of isolation, and in 11 of 12 participating hospitals. Bacteroides vulgatus and isolates from decubitus ulcers were associated with increased resistance. During 2001, trovafloxacin and moxifloxacin resistance among blood isolates was 27% and 52%, respectively. The association between increased resistance and year of isolation remained significant after adjustment for hospital, species and site of isolation. CONCLUSIONS: Fluoroquinolone resistance among Bacteroides isolated in the US has markedly increased during the years 1994 to 2001. High rates of resistance among blood isolates are of particular concern.