Submitted to: Safepork
Publication Type: Proceedings
Publication Acceptance Date: 7/29/2005
Publication Date: 9/6/2005
Citation: Anderson, T.J., Poole, T.L., Anderson, R.C., Nisbet, D.J. 2005. Persistence of Salmonella typhimurium in porcine gut microflora. Proceedings of SafePork 2005. p. 280-282. Interpretive Summary: Public health officials are concerned that the use of antibiotics by farmers may lead to the development of microbial populations resistant to many antibiotics used to treat medically important diseases. In the present study, we tested the competitive fitness of a Salmonella Typhimurium, a common foodborne pathogen found in the gut of pigs, when grown in the presence or absence of the antibiotic chlortetracycline. We found that the chlortetracycline was effective in eliminating the Salmonella although we also observed that the pig’s own beneficial gut bacteria were also able to eliminate the Salmonella, but to a slightly lesser extent. If the Salmonella bacterium was first made resistant to the antibiotic chlortetracycline; we found that it was able to persist in the presence of chlortetracycline. Surprisingly, we found that this chlortetracycline-resistant Salmonella appeared to be more competitive against the pig’s beneficial gut bacteria even when the antibiotic was not present. This research helps elucidate mechanistic aspects of antimicrobial resistance development and provides important information to help producers continue to produce safe and affordable pork products for the American consumer.
Technical Abstract: Chlortetracycline administration, at 55 mg/l, to a continuous flow culture of mixed porcine gut bacteria enhanced the rate of clearance of a chlortetracycline resistant Salmonella Typhimurium from the culture, although the Salmonella was eventually excluded from the culture by 8 d post challenge. As expected, chlortetracycline administration, at 110 mg/l, to a continuous flow culture of mixed porcine gut bacteria had little effect on the persistence of a chlortetracycline resistant strain of Salmonella Typhimurium. The competitive fitness of this resistant strain was enhanced even in the absence of chlortetracycline indicating that even without the potentially selective effects of chlortetracycline on the continuous flow culture’s resident flora, the resistant Salmonella was more competitive than its sensitive Salmonella counterpart.