Influence of Subtherapeutic Levels of Oxytetracycline on Salmonella typhimurium in Swine, Calves, and Chickens

Abstract

Subtherapeutic levels of oxytetracycline in animal feeds have been evaluated to determine their influence on the relative quantity, prevalence, shedding, and antibiotic susceptibility of Salmonella typhimurium in swine, calves, and chickens, when compared with nonmedicated controls. The medicated groups were fed rations containing oxytetracycline commencing 5 days prior to oral inoculation with S. typhimurium and continuing through a 28-day post-inoculation period. Colonization ofS. typhimurium occurred in all three animal species as evidenced by clinical signs ofinfection and/or colony counts in feces measured on seven separate occasions over the 28-day observation period. The accumulated data demonstrate that the subtherapeutic use of oxytetracycline did not bring about any increases in the quantity, prevalence, or shedding of S. typhimurium in swine, calves, and chickens. In fact, the medication generally brought about a decrease in the percentage of animals carrying S. typhimurium during the study period. In contrast to results in swine and calves, there was a significant occurrence of S. typhimurium resistance to oxytetracycline in chickens. Resistant colonies were isolated from chickens sporadically but never on more than two consecutive test periods. These isolates were also resistant to streptomycin, but not to the other six antibiotics tested. The population of resistant S. typhimurium isolated from medicated chickens was no larger than that of susceptible S. typhimurium isolated from the nonmedicated animals. It is concluded that no evidence has been obtained which would relate the continuous low-level feeding of oxytetracycline for a 4-week period to an increased incidence of disease in animals or as a hazard to humans.

Influence of Subtherapeutic Levels of a Combination of Neomycin and Oxytetracycline on Salmonella typhimurium in Swine, Calves, and Chickens

“…DISCUSSION Some of the difficulties involved in determining the proper inoculum size and route of challenge allowing colonization without death were presented in an earlier report (2). Clinical signs of disease were apparent in swine and calves when using S. typhimurium at a concentration ANTImiCEOB.…”

“…The strains ofS. typhimurium used were the same as those previously reported (2). All strains produced an acid butt with H2S and an alkaline slant in triple sugar iron agar (TSI; Difco Laboratories, Detroit, Mich.), were urease negative, agglutinated with Salmonella group B antiserum (BBL, Cockeysville, Md.…”

“…and statistical analysis, were the same as those previously reported (2). The oxytetracycline resistance in E. coli was examined after random lotting of animals but before the start of treatment.…”

“…Recently (2) we reported on the influence of oxytetracycline on Salmonella typhimurium in animals. Generally the subtherapeutic use of oxytetracycline brought about a decrease in the percentage of animals carrying S. typhimurium and did not bring about any increase in the quantity, prevalence, or shedding of S. typhimurium in swine, calves, and chickens.…”

Effect of Feeding Chlortetracycline on the Reservoir of Salmonella typhimurium in Experimentally Infected Swine

“…CTC also reduced the number of tissues that were positive for Salmonella at the end of the 30-day experiment. In another study, in which swine were experimentally infected with a strain of S. typhimurium that was susceptible to oxytetracycline, the feeding of oxytetracycline at 150 g/ton of diet (approximately 165 mg/kg of diet) did not significantly alter the quantity of Salmonella in the feces (5). It did, however, reduce (but not significantly) the number of positive samples.…”