Antimicrobial Use and Emerging Resistance of Salmonella typhimurium in Dairy Cattle (1998-02804)

Antibiotic-resistant Salmonella infections in human are an increasing public health problem.The use of antibiotics in food producing animals for disease prevention or treatment and to enhance growth potentially selects for resistant Salmonella strains whichmay be transmitted to humans. Livestock investigations are needed to identify practices associated with the emergence of Salmonella resistant to antibiotics currently important in human medicine. This project will investigate the effect of antibiotic treatment of clinical salmonellosis in dairy cattle on the occurrence of antibiotic-resistant Salmonella typhimurium, a major animal and human pathogen. This will be done by identifying dairy herds with Salmonella typhimurium-infected cattle based on diagnostic laboratory culture results, obtaining antibiotic treatment information from farm recordsand collecting fecal samples from cattle on the farm for Salmonella isolation and determination of resistance patterns. The association between cattle from the same herd will be analyzed. The characteristics of study farms will be typical of large segment of the U.S. dairy industry. The study results will provide valuable information on the emergence of antibiotic-resistant Salmonella typhimurium and specific drug-use practices which are associated with resistance. This will allow implementation of changes on farms designed to reduce thedevelopment of antibiotic-resistant bacteria and thereby decrease foodbome or direct transmission of resistant strains from dairy cattle to people. The project will also contribute data needed for policy decisions by regulatory agencies related to antibiotic use in food producing animals.