| This thesis is an investigation of risk factors associated with antimicrobial resistance among commensal bacteria from pigs and farm residents on 47 farrow-to-finish swine farms. The prevalences of antimicrobial resistance of fecal Escherichia coli and fecal Enterococcus species have been described. Fecal samples from humans and pooled fecal samples from weaner and finisher pigs were used to isolate enterococci and E. coli for testing of susceptibility to various antimicrobials. The overall prevalence of resistance to one or more antimicrobials was 90%, 98.5%, 25% and 99% for pig E. coli, pig enterococci, human E. coli, and human enterococci respectively. Multiple resistance to as many as 11, 16, 6, and 11 antimicrobials for pig E. coli, pig enterococci, human E. coli, and human enterococci, respectively, was observed. Enterococcus avium, E. casseliflavus, E. durans, E. faecalis, E. faecium, E. gallinarum and E. hirae were recovered from pigs and humans. In addition, E. dispar was recovered from pigs only.; In-feed antimicrobial medication was used primarily in weaner rations and to a lesser extent in the other age groups. Logistic regression was used to model risk factors for antimicrobial resistance. In-feed medication of weaner pigs was a consistent risk factor for resistance in all the data. There was evidence of cross-resistance, e.g. tylosin use was associated with erythromycin resistance in the enterococci data, and co-selection, e.g. ceftiofur use was associated with tetracycline resistance in the E. coli data. People who experienced diarrhea within 3 months prior to this study and those who spent more time in the pig barns consistently had higher odds of antimicrobial resistance in logistic regression models. Consumption of antimicrobials by farmers increased the odds of antimicrobial resistance in human E. coli and enterococci in several models.; Overall, these results suggest that use of antimicrobials in pigs is associated with and maintain resistance in both pigs and humans. Commensal enteric bacteria from pigs and humans may constitute a significant source of resistance genes that may flow between pigs and humans through the food chain, environment and/or direct exposure. |
