Isolation and characterization of Clostridium difficile from porcine and bovine feces
Thitaram, Sutawee Narint
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Clostridium difficile is recognized as a nosocomial pathogen associated with antimicrobial drug-associated diarrhea and pseudomembranous colitis in humans. Community-acquired C. difficile-associated diarrhea has been increasingly reported. The presence of C. difficile in 345 swine fecal samples, 1,325 dairy cattle fecal samples, and 371 environmental samples from dairy cattle farms were examined. Isolates were tested for their susceptibility to 9 antimicrobials and characterized for their relatedness. In the process, two isolation techniques, single and double alcohol shock, were evaluated for the recovery of C. difficile and two typing methods, repetitive extragenic palindromic-polymerase chain reaction (rep-PCR) and pulse-field gel electrophoresis (PFGE), were compared. Fifty five (15.9%) swine fecal samples, 32 (2.4%) dairy cattle fecal samples and 32 (8.6%) dairy cattle environmental samples were positive for C. difficile by either single or double alcohol shock. Double alcohol shock was significantly better than single alcohol shock for the recovery of C. difficile in swine feces. There was no significant difference for the recovery of C. difficile between any combination of isolation methods and media observed in dairy cattle feces. While in environmental samples, double alcohol shock plating to cycloserine-cefoxitin fructose agar (CCFA) was found to be a method of choice for the recovery of C. difficile. All isolates were susceptible to amoxicillin-clavulanic acid, metronidazole, and vancomycin while a small number of isolates (1%) were susceptible to rifampicin. All isolates were resistant to levofloxacin. A total of 135 (71.8%), 30(16%), 25 (13.3%), and 10 (5.3%) isolates were resistant to clindamycin, ampicillin, erythromycin, and linezolid, respectively. Both typing methods demonstrated wide genetic variation among C. difficile strains. Rep-PCR findings were relatively comparable to those obtained by PFGE. A high percentage of indistinguishable isolates between human and animal was found. This suggests that there is potential for foodborne or interspecies transmission.