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Effects of antimicrobials fed as dietary growth promoters on faecal shedding of Campylobacter, Salmonella and shiga-toxin producing Escherichia coli in swine

J. E. Wells, N. Kalchayanand, E. D. Berry, W. T. Oliver
Journal of Applied Microbiology 2013 v.114 no.2 pp. 318-328
Campylobacter coli, Escherichia coli, Salmonella, Shiga toxin, bacitracin, chlortetracycline, diet, feces, genes, medicated feeds, pathogens, piglets, swine feeding, zoonoses
Aims: To determine if antimicrobials commonly used in swine diets to improve growth and reduce disease affect zoonotic pathogen shedding in feces. Methods and Results: Barrows (n = 160) were sorted by weight into 2 treatments at 10 weeks of age, and fed growing, grow-finishing, and finishing diets in 4-week feeding periods. For each feeding phase, diets were prepared without (A-) and with (A+) dietary antimicrobials (chlortetracycline, 0 to 8 wk; bacitracin, 9 to 12 wk) typical of the U.S. when applied by producers. At wk 0, 4, 8, 9, 10, and 12 of the study, fecal swabs or grabs were collected for analyses. Campylobacter spp. was absent at wk 0, but prevalence increased over time with most isolates being identified as Campylobacter coli. When chlortetracycline was used in A+ diets (wk 4 and 8), prevalence for Campylobacter spp., pathogenic E. coli O26 and stx genes were lower in feces. On wk 12 after the shift from chlortetracycline to bacitracin, Campylobacter spp. and stx genes were higher in feces from piglets fed A+ diet, and pathogenic E. coli O26 was not detected. Pathogenic E. coli serogroups O26, O103, and O145 were isolated throughout the study and their prevalence did not differ due to diet. Pathogenic E. coli serogroups O111 and O121 were never found in the piglets, and Salmonella spp. prevalence was low. Conclusions: Diets with chlortetracycline reduced pathogen shedding, but switching to bacitracin prior to harvest increased pathogen shedding compared to the diets free of antimicrobials. Significance and Impact of Study: Inclusion of antimicrobials in the diet can affect zoonotic pathogen shedding in feces of swine.