Biological effects of bacitracin as a therapeutic agent and growth promoting compound

Abstract

Bacitracin is a peptide antibiotic and it has several effects on the microbial population of the intestines that could account for its growth‐promoting ability. Enterotoxigenic E. coli is a major pathogen of weaned pigs and is responsible for significant death loss and retardation in weight gain. We found in in vitro studies that bacitracin at sub‐inhibitory concentrations (390 to 780 μg/ml) preferentially selected for the outgrowth of tetracycline sensitive bacteria from among a population of tetracycline resistant and tetracycline sensitive E. coli and Salmonella. Two E. coli strains were used and showed that bacitracin did select Tetracycline sensitive bacteria (P < 0.05). Nine tetracycline resistant and nine tetracycline sensitive Salmonella strains were pooled in this study. Twenty‐five percent more tetracycline sensitive bacteria were found in LB broth containing bacitracin at the sub‐inhibitory concentration (P < 0.01). These findings suggested that a possible benefit from using bacitracin as a feed additive might be to reduce the Tetrpopulation of pathogens in the intestinal tract. In studies utilizing newly weaned piglets, we established that a feed level concentration of bacitracin in the starter diet did enable piglets to clear a pathogenic bacterium at a faster rate than was the case when piglets were placed on antibiotic‐free feed.Supported by Alphamra Inc., the South Dakota Agricultural Experiment Station, and the South Dakota Center for Infectious Disease Research and Vaccinology