Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/2012
Publication Date: 2/20/2013
Citation: Wells, J., Kalchayanand, N., Berry, E.D., Oliver, W.T. 2013. Effects of antimicrobials fed as dietary growth promoters on faecal shedding of Campylobacter, Salmonella and shiga-toxin producing Escherichia coli in swine. Journal of Applied Microbiology. 114(2):318-328.
Interpretive Summary: For more than five decades, antibiotics have been fed at low levels to swine to improve performance. In recent years there has been increasing demand to remove these dietary treatments. The growth promoting benefits of dietary antibiotics have been well documented, but the impact of these supplements on pathogen shedding has not been studied in detail. The effects of dietary antimicrobials on the fecal shedding for Campylobacter, Salmonella, pathogenic E. coli, and shiga-toxigenic E. coli were determined in pigs during a 12-week feeding period. Chlortetracycline was fed from 0 to 8 weeks and bacitracin was fed from 9 to 12 weeks. Animals fed diets with and without low levels of chlortetracycline shed shiga-toxigenic E. coli similarly, but had lower Campylobacter, and pathogenic E. coli when fed the chlortetracycline. Animals fed diets with and without low levels of bacitracin also shed pathogenic E. coli and shiga-toxigenic E. coli similarly, but had higher Campylobacter when fed bacitracin. Presence of the bacterial genes for shiga-toxin production was highest at time of harvest when bacitracin was fed. Inclusion of antimicrobials in the diet can affect pathogen shedding in feces of swine.
Technical Abstract: 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.