Clostridium perfringens Type A Isolates of Animal Origin with Decreased Susceptibility to Metronidazole Show Extensive Genetic Diversity.

Metronidazole (MTZ) is a first-line drug for the treatment of human infections caused by anaerobic bacteria. Although most Clostridium perfringens isolates are susceptible to metronidazole, a number of strains with decreased susceptibility have been obtained in clinical and environmental surveys. However, little is known yet about the toxinotype and genetic diversity of metronidazole-resistant C. perfringens strains. We tested for susceptibility to metronidazole and assessed the toxigenic status and amplified fragment length polymorphism (AFLP) diversity of a collection of 80 C. perfringens isolates of animal origin. In vitro susceptibility testing by the standard agar dilution technique revealed that 22 isolates (27.5% of total) were susceptible to metronidazole, 54 (67.5%) intermediate susceptible, and four (5%) resistant. All isolates belonged to toxinotype A, and two, 41 and 17, of them yielded a positive PCR result for presence of the gene encoding for enterotoxin (cpe), the consensus form of β2 toxin (cpb2) and the atypical form of β2 toxin, respectively. AFLP fingerprinting classified isolates into 65 genotypes indicating a high molecular diversity among isolates in this study, and this diversity was reflected among isolates from each susceptibility category. In conclusion, the results of this study revealed extensive genetic diversity among C. perfringens type A isolates regardless of their susceptibility to metronidazole.