Sensitive test for screening for Staphylococcus aureus in bovine mastitis by broth cultivation and PCR

An assay was developed and evaluated for screening for Staphylococcus aureus in milk samples from cases of bovine mastitis by overnight cultivation in a broth containing 7-5 per cent sodium chloride, followed by PCR to amplify the nuc gene. The assay could detect concentrations of S aureus as low as 1 colony-forming unit/ml milk. Among 106 milk samples collected from individual quarters of lactating cows in one dairy herd and from a bulk tank, S aureus was detected in nine samples by the PCR assay but in only three samples by conventional microbiological culture.