[Show abstract][Hide abstract] ABSTRACT: The objective of this longitudinal ecological study was to examine the relationship between the prevalence of antibiotic-resistant (AR) commensal Escherichia coli isolates from both monthly human wastewater and composite swine fecal samples and the concurrent aggregated monthly antibiotic use recorded within each host species in multi-site vertically integrated swine and human populations. In addition, human vocation (swine worker versus non-swine worker), swine production group, and season were examined as potential confounding variables. Human and swine E. coli isolates (n=2469 human and 2310 swine, respectively) were tested for antimicrobial susceptibility using a commercial broth microdilution system. In the human population, among swine workers the relative odds of tetracycline resistance were increased significantly for tetracycline (class) drug use at the third quartile and above of mean monthly dosage (MMD) (OR=1.8) as compared to the referent category (non-use). The relative odds of ciprofloxacin resistance were significantly increased for ciprofloxacin use in non-swine workers (OR=5.5) as compared to the referent (non-use). The relative odds of tetracycline resistance were increased significantly for chlortetracycline use in medicated feed for the upper tertile of MMD category (OR=2.9) as compared to the referent category (no use) across all swine production groups. While high variability among seasonal samples over the 3-year period was observed, no common seasonal trends relating to antibiotic use and prevalence of resistance over the 3-year period were apparent. The overall effects of concurrent human and swine antibiotic use on AR E. coli levels were inconsistent and modest in this study.
Full-text · Article · Sep 2009 · Preventive Veterinary Medicine
[Show abstract][Hide abstract] ABSTRACT: In a 3-year longitudinal study, we examined the relationship between the seasonal prevalence of antimicrobial-resistant (AR) Escherichia coli isolates from human wastewater and swine fecal samples and the following risk factors: the host species, the production type (swine), the vocation (human swine workers, non-swine workers, and slaughter plant workers), and the season, in a multisite, vertically integrated swine and human population representative of a closed agri-food system. Human and swine E. coli (n = 4,048 and 3,429, respectively) isolates from wastewater and fecal samples were tested for antimicrobial susceptibility, using the Sensititre broth microdilution system. There were significant (P < 0.05) differences among AR E. coli prevalence levels of (i) the host species, in which swine isolates were at higher risk for resistance to tetracycline, kanamycin, ceftiofur, gentamicin, streptomycin, chloramphenicol, sulfisoxazole, and ampicillin; (ii) the swine production group, in which purchased boars, nursery piglets, and breeding boars isolates had a higher risk of resistance to streptomycin and tetracycline; and iii) the vocation cohorts, in which swine worker cohort isolates exhibited lower sulfisoxazole and cefoxitin prevalence than the non-swine worker cohorts, while the slaughter plant worker cohort isolates exhibited elevated cefoxitin prevalence compared to that of non-swine workers. While a high variability was observed among seasonal samples over the 3-year period, no significant temporal trends were apparent. There were significant differences in the prevalence levels of multidrug-resistant isolates between host species, with swine at a higher risk of carrying multidrug-resistant strains than humans. Considering vocation, slaughter plant workers were at higher risk of exhibiting multidrug-resistant E. coli than non-swine workers.
Full-text · Article · Jun 2008 · Applied and Environmental Microbiology