Clonality and Antibiotic Susceptibility of Yersinia enterocolitica Isolated from U.S. Market Weight Hogs

Pigs are the only known animal reservoir of Yersinia enterocolitica strains pathogenic to humans. In this study 106 ail-positive pathogenic Y. enterocolitica isolates, previously recovered from 2793 swine fecal samples (3.8%) collected during National Animal Health Monitoring System's Swine 2000 study, were examined. The presence of the previously described virulence plasmid, expression of plasmid-associated virulence determinants, and serotype were correlated with genotype, expression of YopE protein, and antibiotic susceptibility. Pulsed-field gel electrophoresis using the enzyme XbaI showed that O:3 and O:5 isolates were highly clonal within a serotype regardless of geographic origin. Antimicrobial resistance profiles of 106 isolates of serotypes O:3 and O:5 were evaluated by agar disk diffusion methodology to 16 different antibiotics. All isolates were susceptible to 13 of the 16 tested antimicrobials; resistance was noted to ampicillin, cephalothin, and tetracycline. The presence of the ail gene, virulence plasmid, the expression of virulence determinants, and serotypes indicate that these isolates from U.S. swine are potentially capable of causing human foodborne illness.