Management and treatment of staphylococcal mastitis

Staphylococcal infections cause both clinical and subclinical mastitis and are responsible for the bulk of economic losses due to mastitis on dairies worldwide. Staphylococcal pathogens are divided into two classifications according to the source (contagious or opportunist) and by laboratory identification as coagulase positive or coagulase negative. Staphylococcus aureus, a coagulase-positive staphylococcal pathogen, differs from other staphylococci because it is a contagious pathogen that spreads from cow to cow. It is the most common contagious pathogen in dairy herds and contributes to milk loss, reduced milk quality, and chronic infections. Coagulase-negative staphylococci are generally considered opportunists that colonize the skin surfaces of the teat end, gain entrance to the gland, and produce an intramammary infection (IMI). These staphylococci vary in pathogenicity and are usually nonclinical but, on occasion, produce clinical signs. If the prevalence in the herd is high, however, then infected cows become the major source of the bacteria, with spread from cow to cow. The level of pathogenicity varies with different Staphylococcus species and herd susceptibility. This article deals with two kinds of staphylococci that cause mastitis: Staphylococcus aureus and coagulase-negative staphylococci. The source of infection, the ease of laboratory identification, and the practices used to manage clinical and subclinical mastitis for these two staphylococcal categories makes this a convenient separation.