Salmonella typhimurium, Hydrophobic Antibiotics, and the Intestinal Colonization of Broiler Chicks

In vitro, Salmonella typhimurium is resistant to concentrations of hydrophobic antibiotics (novobiocin, rifampicin, spectinomycin, trimethoprim) which inhibit other bacteria. Some of these antibiotics are used in poultry production. Membrane-disorganizing agents, both metal chelators and polycations, decreased the concentration of trimethoprim that inhibited the growth of S. typhimurium in vitro. Administration of novobiocin, rifampicin, and spectinomycin to the drinking water of young chicks significantly increased cecal colonization of an experimental strain of S. typhimurium. However, trimethoprim significantly reduced number of S. typhimurium in the ceca, even though this organism was resistant to trimethoprim in vitro.