Antimicrobial Susceptibility of Clostridium difficile Clinical Isolates in Iran

Background: Clostridium difficile infection (CDI) is major growing problem in hospitals and its high incidence has been reported in recent years. Objectives: The aim of this study was to investigate the antimicrobial susceptibility patterns of C. difficile clinical isolates against antibiotics commonly used for treatment CDI in hospitalized patients. Material and Methods: During a 12 month study, 75 C. difficile isolates were collected from 390 patients with CDI. All samples were treated with alcohol and yeast extract broth. The treated suspensions were cultured on a selective cycloserine cefoxitin fructose agar (CCFA) supplemented with 5% sheep blood and incubated in anaerobic conditions, at 37 °C for 5 days. Cdd-3, tcdA and tcdB genes were identified using PCR assay. Results: The prevalence of A+B+ , A+ B- and A- B+ strains were 64(85.3%), 5(6.7%) and 6(8%) respectively. In vitro susceptibility of 75 clinical isolates of C. difficile to 5 antimicrobial agents, including metronidazole, vancomycin, clindamycin, erythromycin and cefotaxime were investigated by Clinical and Laboratory Standards Institute (CLSI) agar dilution method. Metronidazole and vancomycin had good activity against C. difficile isolates with MIC90s of 2 and 1 μg/ml, respectively. Seventy one (94.6%) of strains was inhibited by concentrations that did not exceed 2μg/ml for metronidazole. Resistant to metronidazole observed in 5.3% of isolates. Forty three (57.3%) of the isolates were resistant to erythromycin. Of 43 resistant strains to erythromycin, 9 (12%) isolates had high-level MIC of more than 64 μg/ml. All strains were resistant to cefotaxime. Sixty seven (89.3%) isolates were resistant to clindamycin (MIC90s > 256 μg/ml) and only 6.7% were sensitive to clindamycin. Multidrug-resistant (three or more antibiotics) was seen in 36(48%) isolates. Conclusions: Metronidazole and vancomycin still seem to be most effective drugs for treatment CDI.