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.

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.

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.

Efficacy of hospital cleaning agents and germicides against epidemic Clostridium difficile strains.

OBJECTIVE: To compare the effects of hospital cleaning agents and germicides on the survival of epidemic Clostridium difficile strains. METHODS: We compared the activity of and effects of exposure to 5 cleaning agents and/or germicides (3 containing chlorine, 1 containing only detergent, and 1 containing hydrogen peroxide) on vegetative and spore forms of epidemic and non-epidemic C. difficile strains (3 of each). We carried out in vitro exposure experiments using a human fecal emulsion to mimic conditions found in situ. RESULTS: Cleaning agent and germicide exposure experiments yielded very different results for C. difficile vegetative cells, compared with those for spores. Working-strength concentrations of all of the agents inhibited the growth of C. difficile in culture. However, when used at recommended working concentrations, only chlorine-based germicides were able to inactivate C. difficile spores. C. difficile epidemic strains had a greater sporulation rate than nonepidemic strains. The mean sporulation rate, expressed as the proportion of a cell population that is in spore form, was 13% for all strains not exposed to any cleaning agent or germicide, and it was significantly increased by exposure to cleaning agents or germicides containing detergent alone (34%), a combination of detergent and hypochlorite (24%), or hydrogen peroxide (33%). By contrast, the mean sporulation rate did not change substantially after exposure to germicides containing either a combination of detergent and dichloroisocyanurate (9%) or dichloroisocyanurate alone (15%). CONCLUSIONS: These results highlight differences in the activity of cleaning agents and germicides against C. difficile spores and the potential for some of these products to promote sporulation.

Effect of metronidazole on growth and toxin production by epidemic Clostridium difficile PCR ribotypes 001 and 027 in a human gut model.

OBJECTIVES: We compared the behaviour of Clostridium difficile PCR ribotypes 001 and 027 in a human gut model, and compared the responses to metronidazole exposure. METHODS: Using a human gut model primed with pooled human faeces, gut flora bacterial counts, C. difficile total viable counts, spore counts and cytotoxin titres were determined, following exposure to clindamycin, in the absence or presence of metronidazole. RESULTS: Duration of cytotoxin production by C. difficile ribotype 027 was markedly longer than that of ribotype 001 (23 versus 13 days, respectively), but peak toxin titres were similar. During toxin production, total C. difficile ribotype 027 populations had higher proportions of vegetative cells than did ribotype 001 (median 56.33 versus 23.54%). Similarly, total C. difficile ribotype 027 populations remained predominantly as vegetative cells for longer than did ribotype 001 (20 versus 9 days). The effects of metronidazole on C. difficile were markedly less than expected. Titres of C. difficile ribotype 001 cytotoxin were reduced but recurred following metronidazole administration. C. difficile ribotype 027 cytotoxin titres in the distal section of the gut model were unaffected by metronidazole. These observations correlated with poor metronidazole concentrations. CONCLUSIONS: Duration of cytotoxin production by C. difficile ribotype 027 markedly exceeds that of ribotype 001. Sub-optimal gut concentrations of metronidazole, possibly due to inactivation by components of normal gut flora, are associated with continued toxin production. These findings may help to explain the increased severity of symptoms and higher case-fatality ratio associated with infections due to C. difficile ribotype 027.

Tigecycline does not induce proliferation or cytotoxin production by epidemic Clostridium difficile strains in a human gut model.

OBJECTIVES: Data on the risk of Clostridium difficile infection (CDI) associated with specific antibiotics are difficult to obtain because of confounding clinical factors. It is particularly important to evaluate the propensity of new antibiotics to induce CDI. We have examined the propensity of tigecycline to induce CDI using a human gut model. METHODS: We used a three-stage chemostat human gut model to study the effects of tigecycline on indigenous gut microflora and C. difficile. Two epidemic C. difficile were studied in separate experiments: PCR ribotype 001 (UK, CD001) and PCR ribotype 027 (North America, CD027). Tigecycline MICs for 39 C. difficile representing 19 distinct PCR ribotypes were also determined. RESULTS: Tigecycline MICs were 0.06 mg/L for all the C. difficile strains. Peak tigecycline concentrations in the gut model were 10.9 and 11.7 mg/L in CD027 and CD001 experiments, respectively. Tigecycline instillation invoked marked decreases in numbers of bacteroides and bifidobacteria (10(7)-10(8) cfu/mL) and lesser reductions in facultative anaerobes. Despite markedly altered gut microflora, CD001 and CD027 remained as spores for the duration of the experiment, with no evidence of proliferation or cytotoxin production. CONCLUSIONS: Tigecycline exposure did not induce C. difficile proliferation or cytotoxin production despite reduced competing microflora. The potency of tigecycline against C. difficile may contribute to the low risk of CDI induction. Factors other than gut microflora colonization resistance may be important in preventing C. difficile spore germination, proliferation and cytotoxin production.