Reduced Susceptibility To Metronidazole Research Articles

840. Clinical Failure Rates Associated with Hemin-induced Metronidazole Resistance in Clostridioides difficile

BackgroundCurrent guidelines suggest limiting metronidazole (MTZ) use due to increased treatment failures in patients with Clostridioides difficile infections (CDI). We hypothesized that an increase in the minimum inhibitory concentration (MIC) of MTZ to C. difficile may contribute to these poor response rates. The objective of this study was to examine clinical response rates in patients with CDI based on MTZ MIC and stratified by receipt of MTZ treatment.Methods Clostridioides difficile-positive stool samples collected from 2017 to 2018 as part of routine care at two hospital systems in Houston, Texas were collected for MIC determination at 24 h to MTZ by broth microdilution following incorporation of 5 mg/L of hemin. The primary outcome was initial clinical success by Day 7 of treatment in those with MICs ≥1 vs. <1. Results were stratified based on receipt of MTZ within 48 hours of diagnosis. Study objectives were tested using χ 2 and multivariable logistic regression analyses.ResultsA total of 235 C. difficile samples were included, of which 73 (31%) had an MTZ MIC ≥1. Overall, 72% received MTZ within the first 48 hours. Clinical success rates differed based on disease severity (77% in nonsevere, 64% in severe/fulminant; P = 0.03) and infecting ribotype (52% in RT 027, 75% in non-RT 027; P = 0.014). In patients with MTZ receipt, clinical success rates were higher in patients infected with strains with an MTZ MIC < 1 (76%) compared with those with an MIC ≥1 (60%; P = 0.031). The difference in initial clinical success was not different in those that did not receive MTZ (78% for MIC <1 vs. 65% for MIC ≥1, P = 0.28). After controlling for disease severity, treatment failure was higher in patients infected with strains with an MTZ MIC ≥1 and treated with MTZ (OR 2.1; 95% CI, 1.01–4.35; P = 0.048) but not for those with an MIC ≥1 treated with other therapies (OR 1.9; 95% CI, 0.62–5.6; P = 0.27).ConclusionThis study provides the first preliminary evidence of an association between reduced metronidazole susceptibility and decreased clinical success rates. Larger studies are warranted to validate these findings.Disclosures All Authors: No reported Disclosures.

710. Increased Clinical Failure Rates Associated with Reduced Metronidazole Susceptibility in Clostridioides difficile

BackgroundCurrent national guidelines suggest limiting metronidazole (MTZ) use due to increased treatment failures in patients with Clostridioides difficile infections (CDI). However, the reason for these increased failure rates is unclear. We hypothesized an increase in the minimum inhibitory concentration (MIC) of MTZ to C. difficile may contribute to these poor response rates. The objective of this study was to examine clinical response rates in patients with CDI who received MTZ monotherapy vs. other therapies stratified by MTZ susceptibility.MethodsStool samples that tested positive for C. difficile (2017–2018) were collected from two large academic hospital systems in Texas. C. difficile was isolated from stool and visually screened for growth on heme-containing agar plates with MTZ at 2 mg/L (defined as reduced susceptibility). Blinded investigators reviewed electronic medical records to identify the treatment received and determine clinical success or failure for each patient. Treatment failure rates were assessed in patients that received MTZ monotherapy vs. other therapies stratified by MTZ susceptibility. Results were analyzed using multivariate logistic regression analysis.ResultsA total of 172 C. difficile isolates were included of which 55.8% displayed reduced susceptibility to MTZ. Clinical success rates with MTZ varied based on disease severity (mild-moderate: 80.4%; severe/severe-complicated: 64%). Treatment success rates were higher in patients infected with MTZ susceptible isolates (88.4%) compared with those infected with isolates showing reduced MTZ susceptibility (60.5%; P = 0.004.) In multivariate logistic regression after controlling for disease severity, patients infected with strains displaying reduced MTZ susceptibility and treated with MTZ were more likely to experience treatment failure compared with patients with susceptible isolates (OR = 6.8; 95% CI:1.96–23.8; P = 0.003). In patients given non-MTZ-based therapies, reduced susceptibility to MTZ was not predictive of failure to other treatments.ConclusionThis is the first report to demonstrate that increased clinical failure rates for MTZ monotherapy are associated with reduced susceptibility to MTZ.Disclosures K. Garey, Summit Therapeutics: Collaborator, Research support.

Characterisation of Clostridium difficile strains isolated from Groote Schuur Hospital, Cape Town, South Africa.

The C. difficile infection rate in South Africa is concerning. Many strains previously isolated from diarrhetic patients at Groote Schuur Hospital were ribotype 017. This study further characterised these strains with respect to their clonal relationships, antibiotic susceptibility, toxin production and various attributes impacting on pathogen colonisation. Multilocus variable-number tandem-repeat analysis (MLVA) was used to characterise all C. difficile isolates. Antibiotic susceptibility was determined by E-test and PCR-based analysis of the ermB, gyrA and gyrB genes. Auto-aggregation of cells was measured in broth, and biofilm formation observed in 24-well plates. Toxins were measured using the Wampole C DIFF TOX A/B II kit. Most isolates belonged to the ribotype 017 group. Identical MLVA types occurred in different wards over time, and several patients were infected with identical strains. All isolates were susceptible to vancomycin and metronidazole, but some ribotype 017 isolates showed reduced metronidazole susceptibility (≥2mgl(-1)). Sixty-nine percent of ribotype 017 isolates were resistant to moxifloxacin, and 94% to erythromycin, compared to 0% and 17% resistance, respectively, in non-ribotype 017 isolates. The ermB gene and mutations in the gyrA and/or gyrB genes were linked to erythromycin and moxifloxacin resistance, respectively. Ribotype 017 isolates auto-aggregated more strongly than other isolates and produced lower levels of the TcdB toxin than a reference strain. Certain strains produced strong biofilms. Patient-to-patient transfer and unique infection events could cause the predominance of ribotype 017 strains in the cohort. Multi-drug resistant strains are a potential reservoir for future infections.

In vitro activity of surotomycin against contemporary clinical isolates of toxigenic Clostridium difficile strains obtained in Spain.

OBJECTIVES Clostridium difficile infection (CDI) is the leading cause of hospital-acquired diarrhoea in developed countries. Metronidazole and vancomycin are the mainstay of treatment, although they are associated with treatment failure and recurrence. Novel agents have emerged to address these shortcomings. We investigated the in vitro activity of a novel agent, surotomycin (formerly CB-183,315), and seven other antimicrobial agents against clinical C. difficile isolates. METHODS Antimicrobial susceptibility to surotomycin, fidaxomicin, metronidazole, vancomycin, clindamycin, rifaximin, moxifloxacin and tigecycline was determined for 100 contemporary clinical isolates of C. difficile collected in 2013. MICs were determined by agar dilution according to CLSI procedures. In addition, 10 strains with reduced susceptibility to metronidazole (n = 6) and vancomycin (n = 4) were also tested. Strains were PCR ribotyped. RESULTS The MICs of surotomycin for the 100 isolates ranged from ≤0.06 to 2 mg/L, with a geometric mean (GM) of 0.31 mg/L and an MIC50/90 of 0.25/0.5 mg/L. The MIC range of surotomycin was 0.25-1 mg/L (GM = 0.45 mg/L) for isolates with reduced metronidazole susceptibility and 0.125-0.5 mg/L (GM = 0.25 mg/L) for isolates with reduced vancomycin susceptibility. The three most common ribotypes were 001 (31.0%), 014/020 (17.0%) and 078/126 (17.0%). Ribotype 014/020 exhibited the lowest MICs of surotomycin (GM = 0.22 mg/L); the highest MICs were for ribotype 078/126 (GM = 0.72 mg/L). CONCLUSIONS Surotomycin exhibited potent in vitro activity against all the isolates tested, including those with elevated metronidazole and vancomycin MICs. The potential role of this agent in the treatment of CDI requires further clinical evaluation.

Water Sources in a Zoological Park Harbor Genetically Diverse Strains of Clostridium Perfringens Type A with Decreased Susceptibility to Metronidazole.

The presence of Clostridium perfringens in water is generally regarded as an indicator of fecal contamination, and exposure to waterborne spores is considered a possible source of infection for animals. We assessed the presence and genetic diversity of C. perfringens in water sources in a zoological park located in Madrid (Spain). A total of 48 water samples from 24 different sources were analyzed, and recovered isolates were toxinotyped, genotyped by fluorophore-enhanced repetitive polymerase chain reaction (rep-PCR) fingerprinting and tested for antimicrobial susceptibility. C. perfringens was recovered from 43.8% of water samples and 50% of water sources analyzed. All isolates (n = 70) were type A and 42.9% were β2-toxigenic (i.e., cpb2+), but none contained the enterotoxin-encoding gene (cpe). Isolates belonged to 15 rep-PCR genotypes and most genetic diversity (88%) was distributed among isolates obtained from the same sample. Most isolates displayed intermediate susceptibility (57.1%; MIC = 16μgml-1) or resistance (5.7%; MIC ≥ 32μgml-1) to metronidazole. No resistance to other antimicrobials was detected, although some isolates showed elevated MICs to erythromycin and/or linezolid. Finally, a marginally significant association between absence of cpb2 and decreased susceptibility to metronidazole (MIC ≥ 16μgml-1) was detected. In conclusion, our results reveal a high prevalence of C. perfringens type A in the studied water reservoirs, which constitutes a health risk for zoo animals. The elevated MICs to metronidazole observed for genetically diverse isolates is a cause of additional concern, but more work is required to clarify the significance of reduced metronidazole susceptibility in environmental strains.

In vitro activity of surotomycin against contemporary clinical isolates of toxigenic Clostridium difficile strains obtained in Spain.

Clostridium difficile infection (CDI) is the leading cause of hospital-acquired diarrhoea in developed countries. Metronidazole and vancomycin are the mainstay of treatment, although they are associated with treatment failure and recurrence. Novel agents have emerged to address these shortcomings. We investigated the in vitro activity of a novel agent, surotomycin (formerly CB-183,315), and seven other antimicrobial agents against clinical C. difficile isolates. Antimicrobial susceptibility to surotomycin, fidaxomicin, metronidazole, vancomycin, clindamycin, rifaximin, moxifloxacin and tigecycline was determined for 100 contemporary clinical isolates of C. difficile collected in 2013. MICs were determined by agar dilution according to CLSI procedures. In addition, 10 strains with reduced susceptibility to metronidazole (n = 6) and vancomycin (n = 4) were also tested. Strains were PCR ribotyped. The MICs of surotomycin for the 100 isolates ranged from ≤0.06 to 2 mg/L, with a geometric mean (GM) of 0.31 mg/L and an MIC50/90 of 0.25/0.5 mg/L. The MIC range of surotomycin was 0.25-1 mg/L (GM = 0.45 mg/L) for isolates with reduced metronidazole susceptibility and 0.125-0.5 mg/L (GM = 0.25 mg/L) for isolates with reduced vancomycin susceptibility. The three most common ribotypes were 001 (31.0%), 014/020 (17.0%) and 078/126 (17.0%). Ribotype 014/020 exhibited the lowest MICs of surotomycin (GM = 0.22 mg/L); the highest MICs were for ribotype 078/126 (GM = 0.72 mg/L). Surotomycin exhibited potent in vitro activity against all the isolates tested, including those with elevated metronidazole and vancomycin MICs. The potential role of this agent in the treatment of CDI requires further clinical evaluation.

In vitro susceptibility of Clostridium difficile to SMT19969 and comparators, as well as the killing kinetics and post-antibiotic effects of SMT19969 and comparators against C. difficile.

ObjectivesSMT19969 is a novel antimicrobial under clinical development for the treatment of Clostridium difficile infection (CDI). The objective was to determine the comparative susceptibility of 82 C. difficile clinical isolates (which included ribotype 027 isolates and isolates with reduced metronidazole susceptibility) to SMT19969, fidaxomicin, vancomycin and metronidazole and to determine the killing kinetics and post-antibiotic effects of SMT19969, fidaxomicin and vancomycin against C. difficile.MethodsMICs were determined by agar incorporation. Killing kinetics and post-antibiotic effects were determined against C. difficile BI1, 630 and 5325 (ribotypes 027, 012 and 078, respectively).ResultsSMT19969 showed potent inhibition of C. difficile (MIC90=0.125 mg/L) and was markedly more active than either metronidazole (MIC90 = 8 mg/L) or vancomycin (MIC90 = 2 mg/L). There were no differences in susceptibility to SMT19969 between different ribotypes. Fidaxomicin was typically one doubling dilution more active than SMT19969 and both agents maintained activity against isolates with reduced susceptibility to metronidazole. In addition, SMT19969 was bactericidal against the C. difficile strains tested, with reductions in viable counts to below the limit of detection by 24 h post-inoculation. Vancomycin was bacteriostatic against all three strains. Fidaxomicin was bactericidal although reduced killing was observed at concentrations <20 × MIC against C. difficile BI1 (ribotype 027) compared with other strains tested.ConclusionsThese data demonstrate that SMT19969 is associated with potent and bactericidal activity against the strains tested and support further investigation of SMT19969 as potential therapy for CDI.

In vitro activity of cadazolid against clinically relevant Clostridium difficile isolates and in an in vitro gut model of C. difficile infection

We investigated the in vitro activity of cadazolid against 100 Clostridium difficile isolates and its efficacy in a simulated human gut model of C. difficile infection (CDI). MICs of cadazolid, metronidazole, vancomycin, moxifloxacin and linezolid were determined using agar incorporation for 100 C. difficile isolates, including 30 epidemic strains (ribotypes 027, 106 and 001) with reduced metronidazole susceptibility, 2 linezolid-resistant isolates and 2 moxifloxacin-resistant isolates. We evaluated the efficacy of two cadazolid dosing regimens (250 versus 750 mg/L twice daily for 7 days) to treat simulated CDI. Microflora populations, C. difficile total viable counts and spores, cytotoxin titres, possible emergence of cadazolid, linezolid or quinolone resistance, and antimicrobial concentrations were monitored throughout. Cadazolid was active against all (including linezolid- and moxifloxacin-resistant) C. difficile strains (MIC90 0.125, range 0.03-0.25 mg/L). The cadazolid geometric mean MIC was 152-fold, 16-fold, 9-fold and 7-fold lower than those of moxifloxacin, linezolid, metronidazole and vancomycin, respectively. Both cadazolid dosing regimens rapidly reduced C. difficile viable counts and cytotoxin with no evidence of recurrence. Cadazolid levels persisted at 50-100-fold supra-MIC for 14 days post-dosing. Cadazolid inhibition of enumerated gut microflora was limited, with the exception of bifidobacteria; Bacteroides fragilis group and Lactobacillus spp. counts were unaffected. There was no evidence for selection of strains resistant to cadazolid, quinolones or linezolid. Cadazolid activity was greater than other tested antimicrobials against 100 C. difficile strains. Cadazolid effectively treated simulated CDI in a gut model, with limited impact on the enumerated gut microflora and no signs of recurrence or emergence of resistance within the experimental timeframe.

Emergence of reduced susceptibility to metronidazole in Clostridium difficile

Antimicrobial treatment for Clostridium difficile infection (CDI) has typically been metronidazole, although reports have questioned the efficacy of this option. We screened recently isolated C. difficile (2005-06) for susceptibility to metronidazole and compared results for historic isolates (1995-2001). C. difficile ribotypes 001 (n = 86), 106 (n = 81) and 027 (n = 48) and isolates from the 10 other most prevalent ribotypes in Leeds (n = 57) were screened using spiral gradient endpoint analysis (SGE). C. difficile with metronidazole SGE MICs > or = 6 mg/L were analysed further by agar incorporation and Etest. Multiple-locus variable-number tandem-repeat analysis (MLVA) typing was performed for 28 C. difficile isolates. No reduced metronidazole susceptibility was observed in C. difficile ribotypes 106 and 027 (geometric mean SGE MICs 1.11 and 0.90 mg/L, respectively). In contrast, 21 (24.4%) C. difficile ribotype 001 demonstrated reduced susceptibility to metronidazole (geometric mean SGE MICs 3.51 mg/L, P < 0.001). Variations in susceptibility were observed relating to the method and media, but increased metronidazole MICs were confirmed by an agar incorporation method. Geometric mean agar incorporation MICs for historic C. difficile ribotype 001 (n = 72) were 1.03 (range 0.25-2) mg/L compared with 5.94 (4-8) mg/L (P < 0.001) for recent isolates displaying reduced metronidazole susceptibility. MLVA typing revealed two clonal complexes of C. difficile with reduced susceptibility to metronidazole. We have demonstrated the emergence of reduced susceptibility to metronidazole in 24.4% of the recent C. difficile ribotype 001 isolates from our institution. Our observations could have implications in the clinical setting due to the poor penetration of metronidazole into the colon.

Surveillance de la résistance aux antibiotiques des anaérobies stricts à Gram négatif

Material and method Using an agar reference method (Norma M11-A5, National Committee for Clinical and Laboratory Standards) the minimal inhibitory concentrations of nine antibiotics were determined for 376 anaerobic strains. The following strains were investigated: 254 Bacteroides fragilis group (including 143 B. fragilis), 122 other gram-negative anaerobes ( Bacteroides spp. , Prevotella, Fusobacterium, Porphyromonas, Suterella, Desulfomonas, Veillonella). Results In the B. fragilis group resistance rates were: coamoxyclav 2.8%, ticarcillin 27.5%, ticarcillin–clavulanic acid 1.9%, piperacillin–tazobactam 1.9%, cefoxitin 6.2%, imipenem 0.8%, clindamycin 28.3%, respectively. Based on previous studies, resistance to imipenem remained low in 2003 and was only observed for B. fragilis. Resistance to clindamycin was maintained around 25%. No metronidazole resistance was observed, but decreased susceptibility was found for B. fragilis, B. merdae and Prevotella, as in 4.3% of gram-negative anaerobes. Discussion This study confirms the high resistance rate of gram-negative anaerobes to clindamycin, the efficient activity of imipenem, β-lactam/β-lactamase inhibitor combinations and metronidazole. However, reduced metronidazole susceptibility seems to be increasing.