Effect of tylosin on an experimental Salmonella infection in pigs
Thomas R. Shryock, PhD; Robert A. Elliott, PhD; Travis H. Bennett, MS;Rodney P. Basson, PhD; Richard E. Bowen, DVM, PhD
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Objective: To evaluate the effect of tylosin on an experimentalSalmonella typhimurium infection.
Method: Tylosin was added to the ration of pigs infected withSalmonella (INFMED pigs) at 100 g per ton and fed for a period of 56 dayspost-inoculation and compared to an infected, nonmedicated control group(INF). Fecal samples were taken at least weekly for 56 days from both INFand INFMED pigs. Representative Salmonella isolates from each timepointand pig were tested for susceptibility to 12 different antimicrobial compounds.At the termination of the study, samples of liver, spleen, ileocecal lymphnode, and colon contents were examined for the presence of Salmonella.
Results: There was no difference in the overall mean log10counts of Salmonella between the INFMED and INF groups (P=.75),nor in the prevalence of positive fecal samples between the two groups (P=.66).Medication significantly reduced the mean duration of Salmonellashedding in INFMED pigs compared to INF pigs (P=.05). There was nodifference between treatment groups in the number of Salmonella isolationsfrom tissues taken at necropsy nor on the antimicrobial susceptibility ofSalmonella isolates from the fecal or tissue samples.
Implications: Feeding tylosin to pigs experimentally inoculatedwith S. typhimurium had no effect on the quantity of Salmonellain the feces or on prevalence of Salmonella in the population ofpigs tested. Treatment with tylosin did not change susceptibility to 12antibiotics. However, treatment with tylosin did reduce the duration ofSalmonella shedding in the feces. These findings suggest that tylosindid not reduce the competitive exclusion capacity of the normal intestinalbacteria.