Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/29/2004
Publication Date: 3/20/2005
Citation: Scott, M., Campbell, L.D., Harvey, R.B., Bischoff, K.M., Alali, W.Q., Barling, K.S., Anderson, R.C. 2005. Patterns of antimicrobial resistance among commensal Escherichia coli isolated from integrated multi-site housing and worker cohorts of humans and swine. Foodborne Pathogens and Disease. 2:24-37. Interpretive Summary: There is a concern in human medicine about increasing antibiotic resistance by bacteria. It is felt by the medical community that antibiotics used in food animal production may contribute to the problem. In a study that involved closed populations of humans and swine, we found that antibiotic-resistant bacteria in swine did not pass resistance to the bacteria of their animal caretakers. This is important because it shows that animals may not be the major cause of antibiotic resistance in humans.
Technical Abstract: We examined antimicrobial resistance (AR) phenotypes among commensal Escherichia coli isolated from fecal matter of humans and swine housed in a semi-closed and uniquely integrated multi-site farrow-to-plate operation. Aggregate cohorts of humans consisted of: 1) 'control' groups of consumers, 2) groups of swine workers, and 3) groups of slaughter-plant workers. Analyses of cross-sectional AR data from 472 human and 376 swine isolates are presented. AR phenotypes among these isolates were compared by: 1) host species, 2) facility location, 3) facility type, 4) housing (human) or production (swine) cohort, and 5) sample collection period and time of day. There were significant (p < 0.05) differences in isolates among host-species with swine uniformly at greater risk for: 1) AR to 4 specific antimicrobials (kanamycin, streptomycin, sulfamethoxazole, tetracycline), and 2) for multiple resistance phenotypes (p < 0.0001). Facility type and unit location were more often associated with AR differences among swine isolates than among human isolates. Swine production group was significantly associated with AR prevalence (p < 0.05) for 9 antimicrobials; in general, purchased boars, suckling piglets, weaned piglets and lactating sows were at higher risk of AR. There was no significant (p > 0.05) association of human occupational/consumer cohort with AR prevalence. Several unique AR phenotypes were detected in each of the human- and swine-intake groups. These data establish baseline characteristics for an on-going 3-year longitudinal study designed to further characterize AR phenotype and genotype in this population. Host-, facility-, and cohort-specific data demonstrate that sufficient prevalence differences exist to permit the future quantification of AR transmission, should it occur. Based on these cross-sectional data, occupational exposure to either swine-rearing or swine-slaughter facilities does not appear to be associated with the prevalence of phenotypic resistance among the commensal fecal E. coli isolated from this integrated system.