Comparison of the Prevalence and Genotypic Characteristics of Clostridium difficile in a Closed and Integrated Human and Swine Population in Texas

Clostridium difficile has been recognized as one of the leading causes of nosocomial diarrhea and pseudomembranous colitis in human hospitals and nursing homes since the 1970s; however, recent occurrences of community-acquired cases have led researchers to search for additional sources of these infections. Some of the possible sources being investigated include food animals and retail meat. The objective of this study was to compare the prevalence and genotypic characteristics of C. difficile isolated from a closed population in Texas consisting of both humans and swine. Implicit in this objective, we seek to investigate the possible food safety and occupational risks associated with swine and C. difficile. Isolation of C. difficile was performed utilizing an enrichment technique and restrictive media. Polymerase chain reaction (PCR) was used to test for the presence of the toxin A and B genes, the tcdC gene deletion, and the binary toxin gene. Genotypic characteristics were compared using PCR toxinotyping and pulsed-field gel electrophoresis (PFGE). Antimicrobial susceptibility was tested using commercially available tests (ETest®) for 11 different antibiotics. Statistical comparisons (both parametric and non-parametric, and appropriate to the data) were performed both between and among host species. We tested 2,292 aggregated human wastewater samples and 2,936 swine fecal samples from 2004 to 2006 and found 271 (11.8 percent) and 252 (8.6 percent) to be positive for C. difficile, respectively. The prevalence of C. difficile among swine production groups differed significantly (p<0.05); however, prevalence in the human occupational group cohorts (swine workers and non-workers) did not differ (p=0.81). The majority of the human and swine isolates were a PFGE NAP7 (a variant pattern with 90.5 percent similarity) toxinotype V strain. Antimicrobial resistance levels and multi-resistance patterns were generally similar between host species; however, there was decreased susceptibility (p<0.05) to ampicillin, clindamycin, and imipenem observed in swine isolates, whereas there was decreased susceptibility (p