Surveillance for resistance to metronidazole and vancomycin in genotypically distinct and UK epidemic Clostridium difficile isolates in a large teaching hospital

Jane Freeman, Joanna Stott, Simon D. Baines, Warren N. Fawley and Mark H. Wilcox*

Department of Microbiology, University of Leeds and The General Infirmary, Leeds LS2 9JT, UK


* Corresponding author. Tel: +44-113-392-6818; Fax: +44-113-343-5649; E-mail: Mark.Wilcox{at}Leedsth.nhs.uk

Keywords: C. difficile , infections , treatment

Sir,

Treatment of Clostridium difficile infection (CDI) has changed little since the recognition of the disease in the late 1970s. Currently accepted treatment options are essentially limited to oral metronidazole or vancomycin, ideally following withdrawal of the precipitating antimicrobial. Metronidazole is currently preferred due to its perceived clinical equivalence to vancomycin, in terms of overall response and rates of symptomatic recurrences, and lower cost.1 However, recent reports of poor clinical outcome following metronidazole therapy for CDI2,3 have prompted closer scrutiny of the treatment options and raised the issue of potential for emergence of resistance in C. difficile to metronidazole and vancomycin.

We compared the activity of metronidazole and vancomycin against selected C. difficile isolates from symptomatic patients (n = 74) and their environment (n = 71) over a 6 year period (1995–2001) at the Leeds General Infirmary. Isolates were fingerprinted by RAPD and RS-PCR as described previously.4 We examined 37 UK epidemic clonal isolates (PCR ribotype 00I—confirmed by J. S. Brazier, Anaerobe Reference Unit) from the period 1995–96 (20 from patients and 17 from the hospital environment) and 28 isolates from the period 2000–01 (19 from patients and 9 from the hospital environment). Isolates were selected on the basis of date (at least one patient and one environmental isolate per calendar month were available). All (n = 49) non-epidemic C. difficile isolates recovered from patients (n = 4) or the hospital environment (n = 45) between 1995 and 2001 were examined (16 RAPD types). We also examined the antibiotic susceptibility of 31 UK epidemic clonal C. difficile isolates (PCR ribotype I) recovered sequentially from 13 patients with CDI; two isolates from each of nine patients, three isolates from each of three patients and four isolates from one patient. MICs were determined by agar incorporation. Briefly, following culture in pre-reduced Schaedlers anaerobic broth (Oxoid, UK) at 37°C for 48 h, strains were multipoint inoculated (104 cfu per spot) onto Wilkins-Chalgren agar (Oxoid, UK) and then cultured anaerobically for 48 h. Bacteroides fragilis NCTC 9343 and Staphylococcus aureus NCTC 6571 were used as control organisms.

MICs of metronidazole and vancomycin for UK epidemic clonal (1995–96 and 2000–01), non-epidemic and sequential epidemic clonal C. difficile isolates are shown in Table 1. There was little variation in the MICs of either metronidazole or vancomycin, and with one exception all strains were susceptible. The MICs of metronidazole and vancomycin for the UK epidemic strain from both 1995–96 and 2000–01 were 0.25–1 mg/L and 0.5–1 mg/L, respectively. The solitary, non-toxigenic C. difficile strain showing reduced susceptibility to metronidazole (MIC; 8 mg/L) was isolated from an environmental swab collected towards the beginning of this study period (April 1996).5 This strain was never isolated again, either from patients or the hospital environment, and thus is of doubtful clinical significance. The MICs of metronidazole and vancomycin for isolates recovered from recurrent CDI episodes had MICs essentially the same (within one doubling dilution) as for those from initial symptomatic episodes. Thus, symptomatic recurrences were not associated with reduced susceptibility of C. difficile to either metronidazole or vancomycin. Although we tested limited numbers of patients and isolates associated with treatment failure, we believe this represents the largest number of strains examined from such cases. Sanchez et al. had similar conclusions based on testing isolates from patients in whom metronidazole treatment failed (14 patients out of 632 CDI episodes).6 The MIC (mean ± SD) of metronidazole failure-associated C. difficile isolates (n = 10) was very similar to the MIC of isolates from metronidazole success cases (0.23 ± 0.21 versus 0.29 ± 0.19 mg/L; P = 0.4).


View this table:
[in this window]
[in a new window]
 
Table 1. MICs (mg/L) of metronidazole and vancomycin for non-PCR ribotype I, clonal epidemic 1995–96, clonal epidemic 2000–01 and sequential clonal C. difficile strains

 
Neither metronidazole nor vancomycin resistance is commonly observed among C. difficile isolates. Wong et al. reported a metronidazole-resistant toxigenic isolate among 100 isolates tested.7 We reported the only metronidazole-resistant UK isolate among over 1000 C. difficile strains tested by the PHLS Anaerobe Reference Unit.5 The mechanism behind metronidazole resistance in this strain was not elucidated and the potential for development of metronidazole resistance among clinically relevant toxigenic C. difficile strains is uncertain. Barbut et al. described six C. difficile isolates with MICs of metronidazole ranging from 8 to 32 mg/L among 198 isolates recovered in France in 1991 and in 1997.8 However, five of the six isolates were non-toxigenic strains. No trend for resistance emergence was seen between the two time periods. A single Spanish study reported metronidazole resistance (>16 mg/L) and intermediate vancomycin resistance (4–16 mg/L) in 6.3% and 3.1% of 415 C. difficile strains, respectively,9 but these observations have not been repeated elsewhere.

Our results suggest that resistance to metronidazole or vancomycin remains very uncommon, whether in primary or recurrent CDI settings. Decreased susceptibility of the organism to either agent is unlikely to be the cause of symptomatic recurrence or treatment failure in CDI. Therapeutic failures may occur as a result of other factors, such as poor faecal concentrations of metronidazole, suboptimal host immune response or possibly spore recrudescence.10 However, particularly as the treatment options for CDI are limited, continued vigilance for the emergence of resistance to metronidazole or vancomycin is warranted.

Transparency declarations

No declarations were made by the authors of this paper.

References

1. Gerding DN. Metronidazole for Clostridium difficile-associated disease: is it okay for mom? Clin Infect Dis 2005; 40: 1598–600.[CrossRef][ISI][Medline]

2. Pépin J, Alary M-E, Valiquette L et al. Increasing risk of relapse after treatment of Clostridium difficile colitis in Quebec, Canada. Clin Infect Dis 2005; 40: 1591–7.[CrossRef][ISI][Medline]

3. Musher DM, Aslam S, Logan N et al. Relatively poor outcome after treatment of Clostridium difficile colitis with metronidazole. Clin Infect Dis 2005; 40: 1586–90.[CrossRef][ISI][Medline]

4. Fawley WN, Wilcox MH. Molecular epidemiology of endemic Clostridium difficile infection. Epidemiol Infect 2001; 126: 343–50.[CrossRef][ISI][Medline]

5. Brazier JS, Fawley WN, Freeman J et al. Reduced susceptibility of Clostridium difficile to metronidazole. J Antimicrob Chemother 2001; 48: 741–2.[Free Full Text]

6. Sanchez JL, Gerding DN, Olson M et al. Metronidazole susceptibility in Clostridium difficile isolates recovered from cases of C. difficile-associated disease treatment failures and successes. Anaerobe 1999; 5: 201–4.[CrossRef][ISI]

7. Wong SS-Y, Woo PC-Y, Luk W-K et al. Susceptibility testing of Clostridium difficile against metronidazole and vancomycin by disk diffusion and Etest. Diagn Microbiol Infect Dis 1999; 34: 1–6.[CrossRef][ISI][Medline]

8. Barbut F, Decré D, Burghoffer B et al. Antimicrobial susceptibilities and serogroups of clinical strains of Clostridium difficile isolated in France in 1991 and 1997. Antimicrob Agents Chemother 1999; 43: 2607–11.[Abstract/Free Full Text]

9. Peláez T, Alcalá L, Alonso R et al. Reassessment of Clostridium difficile susceptibility to metronidazole and vancomycin. Antimicrob Agents Chemother 2002; 46: 1647–50.[Abstract/Free Full Text]

10. Freeman J, Baines SD, Jabes D et al. Comparison of the efficacy of ramoplanin and vancomycin in both in vitro and in vivo models of clindamycin-induced Clostridium difficile infection. J Antimicrob Chemother 2005; 56: 717–25.[Abstract/Free Full Text]





This Article
Extract
Full Text (PDF)
All Versions of this Article:
56/5/988    most recent
dki357v1
Alert me when this article is cited
Alert me if a correction is posted
Services
Email this article to a friend
Similar articles in this journal
Similar articles in ISI Web of Science
Similar articles in PubMed
Alert me to new issues of the journal
Add to My Personal Archive
Download to citation manager
Search for citing articles in:
ISI Web of Science (1)
Disclaimer
Request Permissions
Google Scholar
Articles by Freeman, J.
Articles by Wilcox, M. H.
PubMed
PubMed Citation
Articles by Freeman, J.
Articles by Wilcox, M. H.