Characterization of Staphylococcus aureus Isolated from Chronically Infected Dairy Goats

The objectives of this study were to evaluate the presence of intramammary infections (IMI) in dairy buffaloes and examine relationships among IMI, somatic cell counts (SCC), and milk production traits. Two farms in northern Italy were visited monthly for a complete milking season. Quarter-based milk samples were taken at each visit from 46 buffaloes. A total of 1912 samples were assessed in this experiment. Samples were cultured for bacterial presence and tested for SCC and percentages of milk protein and fat. In addition, daily milk yield was recorded from each animal. Prevalence of IMI was high, with 65% of quarters being infected. No animal remained free from IMI throughout the course of the study. Coagulase-negative staphylococci were the most common pathogen (66% of positive samples). The SCC was distinctly higher in infected quarters; 100% of quarters with SCC > 200,000 cell/mL had IMI, whereas 98% of quarters with SCC below this threshold were uninfected. The SCS in these buffaloes was much lower than that commonly observed in dairy cattle; the mean SCS from quarters with IMI was only 2.93. The highest SCS was observed in quarters infected by streptococci. No drastic decrease in milk yield was observed among infected animals, relative to healthy contemporaries. The relatively low SCS and lack of a strong effect on milk yield provide evidence to discourage antibiotic treatment of buffaloes for subclinical IMI during the lactation.