Longitudinal Study of Antimicrobial Resistance among Escherichia coli Isolated from Integrated Multi-site Cohorts of Humans and Swine

Department of Veterinary Integrative Biosciences; Veterinary Large Animal Clinical Sciences; Department of Nutrition and Food Science, Texas A&M University, College Station, Texas 77843, USA; and Food and Feed Safety Research Unit, USDA-ARS-SPARC, College Station, Texas 77845, USA

^* To whom correspondence should be addressed. Email: hmscott{at}cvm.tamu.edu.

	Abstract

In a three-year longitudinal study, we examined the relationship between the seasonal prevalence of antimicrobial-resistant (AR) E. coli isolated from human wastewater and swine fecal samples and the following risk factors: host species, production type (swine), vocation (human swine workers, non-swine workers, and slaughter-plant workers), and season in a multi-site vertically integrated swine and human population representative of a closed agri-food system. Human and swine E. coli (N = 4048 and 3429, respectively) isolated from wastewater and fecal samples were tested for antimicrobial susceptibility using the Sensititre^TM broth microdilution system. There were significant (P < 0.05) differences in AR E. coli prevalence between: 1) host-species, with swine isolates at higher risk for resistance to tetracycline, kanamycin, ceftiofur, gentamicin, streptomycin, chloramphenicol, sulfisoxazole, and ampicillin, 2) swine production group, with purchased boars, nursery piglets, and breeding boars isolates at a higher risk of resistance to streptomycin and tetracycline, and 3) vocation, with swine worker cohort isolates exhibiting lowered sulfisoxazole and cefoxitin prevalence compared to non-swine worker cohorts, while slaughter-plant worker cohort isolates exhibited elevated cefoxitin prevalence compared to non-swine workers. While high variability among seasonal samples over the 3-year period was observed, no significant temporal trends were apparent. There were significant differences in the prevalence of multi-drug resistance isolates between host species, with swine at higher risk than humans of carrying multi-drug resistant strains. Considering vocation, slaughter-plant workers were at higher risk of exhibiting multi-drug resistance E. coli than non-swine workers.