Variation in Weekly Shedding Pattern of Staphylococcus aureus in Naturally Occurring Intramammary Infections

Abstract

Despite improvements in management, prevention, and treatment, mastitis accounts for 26% of morbidity on US dairies, making it the most prevalent and costly disease of dairy cattle. In total, it is estimated that 70-80% of this loss is due to subclinical intramammary infections (IMI) such as Staphylococcus aureus (SA). The most prevalent contagious mastitis pathogen in the United States, SA was detected in 43% of bulk tanks examined. The control of SA is contingent on accurate diagnosis of IMI, yet there remains no definitive standard for the diagnosis of a SA IMI. Studies following cows experimentally infected with the Newbould SA strain concluded that SA was shed in a cyclical pattern and that consecutive samples were necessary to accurately diagnosis a SA IMI. Since then, new technologies, such as pulse field gel electrophoresis (PFGE) used to compare strain relatedness, have brought into question the usefulness of research based on experimental SA infections. The goal of this study was to evaluate bacterial shedding patterns of SA, specifically the influence of clonal relatedness of SA on the shedding patterns of bacteria in naturally occurring SA infections.