The growth of compact and diffuse variants of Staphylococcus aureus in bovine mastitic and normal whey.

Strains of Staphylococcus aureus producing either diffuse or compact colonies in serum-soft agar were grown in bovine normal and mastitic whey. Bacterial growth was followed by automated turbidometry. Compact strains multiplied faster and to higher final numbers in mastitic whey than diffuse strains, whereas diffuse strains grew to higher numbers in normal whey. Nutrients (hemolysed bovine blood, bovine serum, proteose-peptone) were added to normal whey to enhance bacterial growth as in mastitic whey. The growth-promoting effect of these nutrients was dose-dependent for compact strains but not for diffuse strains. The difference in the growth characteristics of diffuse and compact strains in bovine whey explains some aspects of the pathogenesis of bovine mastitis.