Para-cresol production by Clostridium difficile affects microbial diversity and membrane integrity of Gram-negative bacteria.

Clostridium difficile is a Gram-positive spore-forming anaerobe and a major cause of antibiotic-associated diarrhoea. Disruption of the commensal microbiota, such as through treatment with broad-spectrum antibiotics, is a critical precursor for colonisation by C. difficile and subsequent disease. Furthermore, failure of the gut microbiota to recover colonisation resistance can result in recurrence of infection. An unusual characteristic of C. difficile among gut bacteria is its ability to produce the bacteriostatic compound para-cresol (p-cresol) through fermentation of tyrosine. Here, we demonstrate that the ability of C. difficile to produce p-cresol in vitro provides a competitive advantage over gut bacteria including Escherichia coli, Klebsiella oxytoca and Bacteroides thetaiotaomicron. Metabolic profiling of competitive co-cultures revealed that acetate, alanine, butyrate, isobutyrate, p-cresol and p-hydroxyphenylacetate were the main metabolites responsible for differentiating the parent strain C. difficile (630Δerm) from a defined mutant deficient in p-cresol production. Moreover, we show that the p-cresol mutant displays a fitness defect in a mouse relapse model of C. difficile infection (CDI). Analysis of the microbiome from this mouse model of CDI demonstrates that colonisation by the p-cresol mutant results in a distinctly altered intestinal microbiota, and metabolic profile, with a greater representation of Gammaproteobacteria, including the Pseudomonales and Enterobacteriales. We demonstrate that Gammaproteobacteria are susceptible to exogenous p-cresol in vitro and that there is a clear divide between bacterial Phyla and their susceptibility to p-cresol. In general, Gram-negative species were relatively sensitive to p-cresol, whereas Gram-positive species were more tolerant. This study demonstrates that production of p-cresol by C. difficile has an effect on the viability of intestinal bacteria as well as the major metabolites produced in vitro. These observations are upheld in a mouse model of CDI, in which p-cresol production affects the biodiversity of gut microbiota and faecal metabolite profiles, suggesting that p-cresol production contributes to C. difficile survival and pathogenesis.

Comparison of planktonic and biofilm-associated communities of Clostridium difficile and indigenous gut microbiota in a triple-stage chemostat gut model.

BACKGROUND: Biofilms are characteristic of some chronic or recurrent infections and this mode of growth tends to reduce treatment efficacy. Clostridium difficile infection (CDI) is associated with a high rate of recurrent symptomatic disease. The presence and behaviour of C. difficile within intestinal biofilms remains largely unexplored, but may factor in recurrent infection. METHODS: A triple-stage chemostat gut model designed to facilitate the formation of intestinal biofilm was inoculated with a pooled human faecal emulsion. Bacterial populations were allowed to equilibrate before simulated CDI was induced by clindamycin (33.9 mg/L, four times daily, 7 days) and subsequently treated with vancomycin (125 mg/L, four times daily, 7 days). Indigenous gut microbiota, C. difficile total viable counts, spores, cytotoxin and antimicrobial activity in planktonic and biofilm communities were monitored during the 10 week experimental period. RESULTS: Vancomycin successfully treated the initial episode of simulated CDI, but ∼18 days after therapy cessation, recurrent infection occurred. Germination, proliferation and toxin production were evident within planktonic communities in both initial and recurrent CDI. In contrast, sessile C. difficile remained in dormant spore form for the duration of the experiment. The effects of and recovery from clindamycin and vancomycin exposure for sessile populations was delayed compared with responses for planktonic bacteria. CONCLUSIONS: Intestinal biofilms provide a potential reservoir for C. difficile spore persistence, possibly facilitating their dispersal into the gut lumen after therapeutic intervention, leading to recurrent infection. Therapeutic options for CDI could have increased efficacy if they are more effective against sessile C. difficile.

Evaluation of antimicrobial activity of ceftaroline against Clostridium difficile and propensity to induce C. difficile infection in an in vitro human gut model.

OBJECTIVES: To examine the effects of exposure to ceftaroline or ceftriaxone on the epidemic Clostridium difficile strain PCR ribotype 027 and the indigenous gut microflora in an in vitro human gut model. Additionally, the MICs of ceftriaxone and ceftaroline for 60 C. difficile isolates were determined. METHODS: Two triple-stage chemostat gut models were primed with human faeces and exposed to ceftaroline (10 mg/L, twice daily, 7 days) or ceftriaxone (150 mg/L, once daily, 7 days). Populations of indigenous gut microorganisms, C. difficile total viable counts, spore counts, cytotoxin titres and antimicrobial concentrations were monitored throughout. MICs were determined by a standard agar incorporation method. RESULTS: In the gut model, both ceftaroline and ceftriaxone induced C. difficile spore germination, proliferation and toxin production, although germination occurred 5 days later in the ceftaroline-exposed model. Toxin detection was sustained until the end of the experimental period in both models. No active antimicrobial was detected in vessel 3 of either model, although inhibitory effects on microflora populations were observed. Ceftaroline was ∼8-fold more active against C. difficile than ceftriaxone (geometric mean MICs, 3.38 versus 28.18 mg/L; MIC90s, 4 versus 64 mg/L; and MIC ranges, 0.125-16 versus 8-128 mg/L). CONCLUSIONS: Ceftaroline, like ceftriaxone, can induce simulated C. difficile infection in a human gut model. However, low in vivo gut concentrations of ceftaroline and increased activity against C. difficile in comparison with ceftriaxone mean that the true propensity of this novel cephalosporin to induce C. difficile infection remains unclear.

Evaluation of NVB302 versus vancomycin activity in an in vitro human gut model of Clostridium difficile infection.

OBJECTIVES: First-line treatment options for Clostridium difficile infection (CDI) are limited. NVB302 is a novel type B lantibiotic under evaluation for the treatment of CDI. We compared the responses to NVB302 and vancomycin when used to treat simulated CDI in an in vitro gut model. METHODS: We used ceftriaxone to elicit simulated CDI in an in vitro gut model primed with human faeces. Vancomycin and NVB302 were instilled into separate gut models and the indigenous gut microbiota and C. difficile total viable counts, spores and toxin levels were monitored throughout. RESULTS: Ceftriaxone instillation promoted C. difficile germination and high-level toxin production. Commencement of NVB302 and vancomycin instillation reduced C. difficile total viable counts rapidly with only C. difficile spores remaining within 3 and 4 days, respectively. Cytotoxin was reduced to undetectable levels 5 and 7 days after vancomycin and NVB302 instillation commenced in vessel 2 and 3, respectively, and remained undetectable for the remainder of the experiments. C. difficile spores were unaffected by the presence of vancomycin or NVB302. NVB302 treatment was associated with faster resolution of Bacteroides fragilis group. CONCLUSIONS: Both NVB302 and vancomycin were effective in treating simulated CDI in an in vitro gut model. C. difficile spore recrudescence was not observed following successful treatment with either NVB302 or vancomycin. NVB302 displayed non-inferiority to vancomycin in the treatment of simulated CDI, and had less deleterious effects against B. fragilis group. NVB302 warrants further clinical investigation as a potentially novel antimicrobial agent for the treatment of CDI.

Mixed infection by Clostridium difficile in an in vitro model of the human gut.

OBJECTIVES: Clostridium difficile infection (CDI) is still a major clinical challenge. Previous studies have demonstrated multiple distinct C. difficile strains in the faeces of patients with CDI; yet whether true mixed CDI occurs in vivo is unclear. In this study we evaluated whether two distinct C. difficile strains could co-germinate and co-proliferate in an in vitro human gut model. METHODS: An in vitro triple-stage chemostat was used to study the responses of two PCR ribotype 001 C. difficile strains following exposure to ceftriaxone at concentrations observed in vivo (7 days). C. difficile viable counts (vegetative and spore forms), cytotoxin titres and indigenous microflora viable counts were monitored throughout the experiment. RESULTS: Both C. difficile strains germinated and proliferated following exposure to ceftriaxone. Cytotoxin production was detected in the gut model following C. difficile spore germination and proliferation. Ceftriaxone elicited reduced viable counts of Bifidobacterium spp. and elevated viable counts of Enterococcus spp. CONCLUSIONS: These data suggest that multiple C. difficile strains are able to proliferate concurrently in an in vitro model reflective of the human colon. Previous studies in the gut model have reflected clinical observations so clinicians should be mindful of the possibility that multiple C. difficile strains may infect patients. These observations augment recent human epidemiological studies in this area.

Non-Toxigenic Clostridioides difficile Strain E4 (NTCD-E4) Prevents Establishment of Primary C. difficile Infection by Epidemic PCR Ribotype 027 in an In Vitro Human Gut Model.

Clostridioides difficile infection (CDI) remains a significant healthcare burden. Non-toxigenic C. difficile (NTCD) strains have shown a benefit in preventing porcine enteritis and in human recurrent CDI. In this study, we evaluated the efficacy of metronidazole-resistant NTCD-E4 in preventing CDI facilitated by a range of antimicrobials in an in vitro human gut model. NTCD-E4 spores (at a dose of 107) were instilled 7 days before a clinical ribotype (RT) 027 (at the same dose) strain (210). In separate experiments, four different antimicrobials were used to perturb gut microbiotas; bacterial populations and cytotoxin production were determined using viable counting and Vero cell cytotoxicity, respectively. RT027 and NTCD-E4 proliferated in the in vitro model when inoculated singly, with RT027 demonstrating high-level cytotoxin (3-5-log10-relative units) production. In experiments where the gut model was pre-inoculated with NTCD-E4, RT027 was remained quiescent and failed to produce cytotoxins. NTCD-E4 showed mutations in hsmA and a gene homologous to CD196-1331, previously linked to medium-dependent metronidazole resistance, but lacked other metronidazole resistance determinants. This study showed that RT027 was unable to elicit simulated infection in the presence of NTCD-E4 following stimulation by four different antimicrobials. These data complement animal and clinical studies in suggesting NTCD offer prophylactic potential in the management of human CDI.

Analysis of biofilm production and expression of adhesion structures of circulating Clostridioides difficile strains from Mexico.

INTRODUCTION: Clostridioides difficile biofilms are believed to protect the pathogen from antibiotics, in addition to potentially contributing to recurrent infections. METHODOLOGY: Biofilm production of 102 C. difficile isolates was determined using the crystal violet staining technique, and detachment assays were performed. The expression levels of cwp84 and slpA genes were evaluated by real-time PCR on selected isolates. RESULTS: More than 70% of isolates (75/102) were strong biofilm producers, and the highest detachment of biofilm was achieved with the proteinase K treatment (>90%). The overall mean expression of cwp84 was higher in RT027 than in RT001 (p=0.003); among strong biofilm-producing strains, the slpA expression was lower in RT027 than in RT001 (p<0.000). CONCLUSIONS: Proteins seem to have an important role in the biofilm's initial adherence and maturation. slpA and cwp84 are differentially expressed by C. difficile ribotype and biofilm production level.

Evaluation of linezolid for the treatment of Clostridium difficile infection caused by epidemic strains using an in vitro human gut model.

OBJECTIVES: Therapeutic options in Clostridium difficile infection (CDI) are limited. We examined linezolid activity in vitro and potential therapeutic efficacy using a gut model of CDI. METHODS: MICs were determined by agar incorporation for 118 diverse C. difficile faecal isolates, including epidemic strains and strains with reduced susceptibility to metronidazole. CDI was established in two gut model experiments using C. difficile epidemic strains (ribotypes 027 and 106) and linezolid was dosed to achieve human gut concentrations. RESULTS: Linezolid demonstrated good in vitro activity against 98% of the isolates. Two isolates (PCR ribotypes 023 and 067) demonstrated resistance to linezolid, although supplementary susceptibility testing of ribotype 023 isolates did not detect further resistance. In a gut model that simulates CDI, linezolid reduced the duration of cytotoxin production by C. difficile PCR ribotype 027 without influencing viable counts of vegetative forms of the organism. C. difficile PCR ribotype 106 viable counts declined at a faster rate than those of PCR ribotype 027 following dosing with linezolid, but cytotoxin titres declined at a similar rate to an untreated control. Gut flora perturbation occurring on linezolid exposure reversed after drug cessation. Recrudescence of spore germination with subsequent cytotoxin was seen with the C. difficile ribotype 106 strain. Resistance to linezolid was not detected either during linezolid instillation or post-dosing. CONCLUSIONS: Linezolid may reduce toxin levels, as reported in staphylococci and streptococci. Further evaluation is warranted of the effect of linezolid on expression of C. difficile toxin, and to investigate potential recurrence of CDI following cessation of linezolid.

Analysis of biofilm production and expression of adhesion structures of circulating Clostridioides difficile strains from Mexico.

INTRODUCTION: Clostridioides difficile biofilms are believed to protect the pathogen from antibiotics, in addition to potentially contributing to recurrent infections. METHODOLOGY: Biofilm production of 102 C. difficile isolates was determined using the crystal violet staining technique, and detachment assays were performed. The expression levels of cwp84 and slpA genes were evaluated by real-time PCR on selected isolates. RESULTS: More than 70% of isolates (75/102) were strong biofilm producers, and the highest detachment of biofilm was achieved with the proteinase K treatment (>90%). The overall mean expression of cwp84 was higher in RT027 than in RT001 (p=0.003); among strong biofilm-producing strains, the slpA expression was lower in RT027 than in RT001 (p<0.000). CONCLUSIONS: Proteins seem to have an important role in the biofilm's initial adherence and maturation. slpA and cwp84 are differentially expressed by C. difficile ribotype and biofilm production level.

Diversity of Circulating Clostridioides difficile Ribotypes in Mexico and Susceptibility to Fidaxomicin, Vancomycin, and Metronidazole.

In this study, we report the results of the epidemiological analysis of Clostridioides difficile ribotypes (RTs) and antimicrobial susceptibility testing. Most isolates were RT027, representing 73% (84/115) of isolates. No isolates with reduced susceptibility to fidaxomicin were found; however, 38 (33.04%) isolates had reduced susceptibility to metronidazole, and 7 isolates (6.1%) had reduced susceptibility to vancomycin. These findings highlight the need for continuous surveillance of C. difficile RTs and antimicrobial susceptibility testing.

Molecular epidemiology of predominant and emerging Clostridioides difficile ribotypes.

There has been an increase in the incidence and severity of Clostridioides difficile infection (CDI) worldwide, and strategies to control, monitor, and diminish the associated morbidity and mortality have been developed. Several typing methods have been used for typing of isolates and studying the epidemiology of CDI; serotyping was the first typing method, but then was replaced by pulsed-field gel electrophoresis (PFGE). PCR ribotyping is now the gold standard method; however, multi locus sequence typing (MLST) schemes have been developed. New sequencing technologies have allowed comparing whole bacterial genomes to address genetic relatedness with a high level of resolution and discriminatory power to distinguish between closely related strains. Here, we review the most frequent C. difficile ribotypes reported worldwide, with a focus on their epidemiology and genetic characteristics.

Characterization of the sporulation initiation pathway of Clostridium difficile and its role in toxin production.

Clostridium difficile is responsible for significant mortality and morbidity in the hospitalized elderly. C. difficile spores are infectious and are a major factor contributing to nosocomial transmission. The Spo0A response regulator is the master regulator for sporulation initiation and can influence many other cellular processes. Using the ClosTron gene knockout system, we inactivated genes encoding Spo0A and a putative sporulation-associated sensor histidine kinase in C. difficile. Inactivation of spo0A resulted in an asporogeneous phenotype, whereas inactivation of the kinase reduced C. difficile sporulation capacity by 3.5-fold, suggesting that this kinase also has a role in sporulation initiation. Furthermore, inactivation of either spo0A or the kinase resulted in a marked defect in C. difficile toxin production. Therefore, Spo0A and the signaling pathway that modulates its activity appear to be involved in regulation of toxin synthesis in C. difficile. In addition, Spo0A was directly phosphorylated by a putative sporulation-associated kinase, supporting the hypothesis that sporulation initiation in C. difficile is controlled by a two-component signal transduction system rather than a multicomponent phosphorelay. The implications of these findings for C. difficile sporulation, virulence, and transmission are discussed.

Tolevamer is not efficacious in the neutralization of cytotoxin in a human gut model of Clostridium difficile infection.

The efficacy of tolevamer, a nonantimicrobial styrene derivative toxin-binding agent, in treating simulated Clostridium difficile infection in an in vitro human gut model was investigated. Tolevamer reduced neither the duration nor magnitude of cytotoxin activity by C. difficile, reflecting poor efficacy observed in recent phase III clinical trials.

Effects of exposure of Clostridium difficile PCR ribotypes 027 and 001 to fluoroquinolones in a human gut model.

The incidence of Clostridium difficile infection is increasing, with reports implicating fluoroquinolone use. A three-stage chemostat gut model was used to study the effects of three fluoroquinolones (ciprofloxacin, levofloxacin, and moxifloxacin) on the gut microbiota and two epidemic C. difficile strains, strains of PCR ribotypes 027 and 001, in separate experiments. C. difficile total viable counts, spore counts, and cytotoxin titers were determined. The emergence of C. difficile isolates with reduced antibiotic susceptibility was monitored with fluoroquinolone-containing medium, and molecular analysis of the quinolone resistance-determining region was performed. C. difficile spores were quiescent in the absence of fluoroquinolones. Instillation of each fluoroquinolone led to C. difficile spore germination and high-level cytotoxin production. High-level toxin production occurred after detectable spore germination in all experiments except those with C. difficile PCR ribotype 027 and moxifloxacin, in which marked cytotoxin production preceded detectable germination, which coincided with isolate recovery on fluoroquinolone-containing medium. Three C. difficile PCR ribotype 027 isolates and one C. difficile PCR ribotype 001 isolate from fluoroquinolone-containing medium exhibited elevated MICs (80 to > or =180 mg/liter) and possessed mutations in gyrA or gyrB. These in vitro results suggest that all fluoroquinolones have the propensity to induce C. difficile infection, regardless of their antianaerobe activities. Resistant mutants were seen only following moxifloxacin exposure.

Activity of vancomycin against epidemic Clostridium difficile strains in a human gut model.

OBJECTIVES: Vancomycin and metronidazole remain the only primary options for the treatment of Clostridium difficile infection (CDI). Recent reports have suggested a superior clinical response to vancomycin therapy compared with metronidazole, but this has been difficult to prove or explain. There are few robust in vitro data of the effects of antibiotic treatment of CDI in a gut reflective setting. METHODS: We used clindamycin to induce high-level toxin production by two epidemic C. difficile PCR ribotypes in a human gut model of CDI. Vancomycin was instilled into the models to achieve in vivo faecal concentrations. C. difficile populations and toxin titres, and gut bacterial populations and vancomycin levels were monitored before, during and after vancomycin instillation. RESULTS: Clindamycin treatment elicited C. difficile germination and high-level cytotoxin production. Vancomycin reduced total viable counts and cytotoxin titres of both C. difficile PCR ribotypes, with no evidence of recurrence before the model runs were ended. C. difficile PCR ribotype 027 populations exhibited greater germination capacity than did PCR ribotype 106. Vancomycin was more rapidly effective against the greater numbers of PCR ribotype 027 vegetative forms. Vancomycin showed no activity against C. difficile spores. CONCLUSIONS: Bacteriological response to vancomycin varies between strains causing CDI, possibly correlating with the extent of germination capacity. Vancomycin effectively reduced vegetative forms and cytotoxin titres of both of the epidemic C. difficile PCR ribotypes evaluated, but showed no anti-spore activity. Comparison with the results of a previous gut model study showed that vancomycin was more effective than metronidazole in reducing C. difficile PCR ribotype 027 numbers and cytotoxin titres.

High sporulation and overexpression of virulence factors in biofilms and reduced susceptibility to vancomycin and linezolid in recurrent Clostridium [Clostridioides] difficile infection isolates.

Clostridium [Clostridioides] difficile infection (CDI) is one of the leading causes of diarrhea associated with medical care worldwide, and up to 60% of patients with CDI can develop a recurrent infection (R-CDI). A multi-species microbiota biofilm model of C. difficile was designed to evaluate the differences in the production of biofilms, sporulation, susceptibility to drugs, expression of sporulating (sigH, spo0A), quorum sensing (agrD1, and luxS), and adhesion-associated (slpA and cwp84) pathway genes between selected C. difficile isolates from R-CDI and non-recurrent patients (NR-CDI). We obtained 102 C. difficile isolates from 254 patients with confirmed CDI (66 from NR-CDI and 36 from R-CDI). Most of the isolates were biofilm producers, and most of the strains were ribotype 027 (81.374%, 83/102). Most C. difficile isolates were producers of biofilm (100/102), and most were strongly adherent. Sporulation was higher in the R-CDI than in the NR-CDI isolates (p = 0.015). The isolates from R-CDI patients more frequently demonstrated reduced susceptibility to vancomycin than isolates of NR-CDI patients (27.78% [10/36] and 9.09% [6/66], respectively, p = 0.013). The minimum inhibitory concentrations for vancomycin and linezolid against biofilms (BMIC) were up to 100 times and 20 times higher, respectively, than the corresponding planktonic MICs. Expression of sigH, spo0A, cwp84, and agrD1 was higher in R-CDI than in NR-CDI isolates. Most of the C. difficile isolates were producers of biofilms with no correlation with the ribotype. Sporulation was greater in R-CDI than in NR-CDI isolates in the biofilm model of C. difficile. The R-CDI isolates more frequently demonstrated reduced susceptibility to vancomycin and linezolid than the NR-CDI isolates in both planktonic cells and biofilm isolates. A higher expression of sporulating pathway (sigH, spo0A), quorum sensing (agrD1), and adhesion-associated (cwp84) genes was found in R-CDI than in NR-CDI isolates. All of these factors can have effect on the recurrence of the infection.

Comparison of oritavancin versus vancomycin as treatments for clindamycin-induced Clostridium difficile PCR ribotype 027 infection in a human gut model.

OBJECTIVES: To compare the efficacy of oritavancin and vancomycin in the treatment of Clostridium difficile infection (CDI) using an in vitro human gut model. METHODS: We induced CDI by instilling clindamycin into an in vitro gut model primed with pooled human faeces and C. difficile ribotype 027 spores. Oritavancin and vancomycin were instilled in separate experiments at levels equivalent to those expected in the faeces (vancomycin) of patients or levels limited by the solubility of the drug (oritavancin). RESULTS: Clindamycin exposure elicited C. difficile proliferation and high-level cytotoxin production in both experiments. Vancomycin instillation reduced vegetative C. difficile numbers within 1 day but did not affect the numbers of C. difficile spores. Oritavancin instillation markedly reduced C. difficile vegetative numbers and spores to below the limits of detection within 2 days. Cytotoxin titres in both experiments declined to the limits of detection after instillation with oritavancin or vancomycin, but did so more quickly (within 5 days) in the vancomycin experiment. Cessation of vancomycin instillation was associated with further C. difficile proliferation and high-level cytotoxin production. Conversely, toxin recrudescence was not observed following cessation of oritavancin. CONCLUSIONS: Both oritavancin and vancomycin were effective in treating clindamycin-induced CDI in a human gut model, but only oritavancin appeared active against spore forms of C. difficile. Furthermore, recurrence of high-level cytotoxin production was observed following vancomycin instillation but not oritavancin. Oritavancin therapy may be more effective in treating CDI than vancomycin, possibly because it may prevent recrudescence of C. difficile spores.

In vitro susceptibility of genotypically distinct and clonal Clostridium difficile strains to oritavancin.

OBJECTIVES: Clostridium difficile infection is a nosocomial disease of increasing importance. First-line treatment is limited to metronidazole or vancomycin. Oritavancin is a lipoglycopeptide with activity against Gram-positive bacteria, including drug-resistant pathogens. MICs of oritavancin, metronidazole and vancomycin for genotypically distinct C. difficile strains, including epidemic C. difficile PCR ribotypes 001 and 027, were determined by agar incorporation and broth macrodilution methods. In agar incorporation methods, the impact of supplements on oritavancin MICs was tested to address oritavancin binding to surfaces. METHODS: Thirty-three genotypically distinct C. difficile strains were identified by PCR ribotyping. Wilkins Chalgren agar incorporation plates containing oritavancin, metronidazole and vancomycin were prepared with and without 0.002% polysorbate-80 (P80) and lysed horse blood (2%). Broth macrodilution MICs of oritavancin, metronidazole and vancomycin were determined in Brucella broth. Inoculated agar incorporation plates and broth macrodilution tubes were cultured anaerobically at 37 degrees C for 48 h. RESULTS: Broth macrodilution MICs were lower than agar incorporation MICs for oritavancin, but not for metronidazole and vancomycin. Oritavancin broth macrodilution MIC(90)s were 2- to 4-fold lower than the corresponding agar incorporation MIC(90)s, while geometric mean MICs were >5-fold lower. Oritavancin broth macrodilution MIC(90)s were approximately 2- and 5-fold lower than those for metronidazole and vancomycin. Metronidazole was the most active antimicrobial agent against C. difficile using agar incorporation methods. Oritavancin agar incorporation MIC(90)s were unaffected by 0.002% P80 and/or 2% lysed horse blood. CONCLUSIONS: Oritavancin was at least 4-fold more potent than vancomycin against the majority (25/33) of C. difficile strains tested by broth macrodilution. Oritavancin activity may be underestimated by agar incorporation methods, regardless of the use of P80 or lysed horse blood.

Emergence of reduced susceptibility to metronidazole in Clostridium difficile.

OBJECTIVES: 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). METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

Circulation of Highly Drug-Resistant Clostridium difficile Ribotypes 027 and 001 in Two Tertiary-Care Hospitals in Mexico.

OBJECTIVE: To assess drug susceptibility and characterize Clostridium difficile ribotypes in isolates from two tertiary-care hospitals in Mexico. METHODS: Isolates were evaluated for genotyping, antimicrobial susceptibility testing and detection of mutations associated with drug resistance. PCR ribotyping was performed using a combination of gel-based and capillary electrophoresis-based approaches. RESULTS: MIC50 and MIC90 were ≥128 mg/L for ciprofloxacin, erythromycin, clindamycin, and rifampicin. There was no reduced susceptibility to metronidazole or tetracycline; however, reduced susceptibility to vancomycin (≥4 mg/L) and fidaxomicin (≥2 mg/L) was detected in 50 (40.3%) and 4 (3.2%) isolates, respectively. Furthermore, the rpoB Arg505Lys mutation was more frequently detected in isolates with high minimum inhibitory concentration (MIC) to rifampicin (≥32 mg/L) (OR = 52.5; 95% CI = 5.17-532.6; p < 0.000). Of the 124 C. difficile isolates recovered, 84 (66.7%) were of ribotype 027, 18 (14.5%) of ribotype 001, and the remainder were other ribotypes (353, 255, 220, 208, 176, 106, 076, 020, 019, 017, 014, 012, 003, and 002). CONCLUSION: Ribotypes 027 and 001 were the most frequent C. difficile isolates recovered in this study, and demonstrated higher MICs. Furthermore, we found four isolates with reduced susceptibility to fidaxomicin, raising a concern since this drug is currently unavailable in Mexican Hospitals.