Identification of Staphylococcus aureus genes expressed during growth in milk: a useful model for selection of genes important in bovine mastitis?

Staphylococcus aureus is a major cause of bovine mastitis. Since gene expre ssion of many bacteria is known to be regulated by the environment, milk ma y play an important role in the regulation of the early steps in the pathog enesis of bovine mastitis by S. aureus. To get insight into the response of S. aureus to the milk environment, a Tn917-lacZ mutant library was generat ed and screened for genes specifically expressed during growth in milk. Twe nty-eight mutants were identified and analysed, Four groups of genes were f ound, involved in cell-wall synthesis. nucleotide synthesis, transcriptiona l regulation and carbohydrate metabolism. A fifth group contained genes wit h hypothetical or unknown functions, Many of the genes identified belonged to biosynthetic pathways of S. aureus and other bacterial species which hav e also been shown to play a role in vivo as determined in murine infection models, Therefore, growth on milk may be an attractive model for the identi fication of genes preferentially expressed during bovine mastitis.