Enterotoxigenic Staphylococcus aureus in bulk milk in Norway

Aims: To investigate the presence of enterotoxigenic Staphylococcus aureus in bulk milk and in a selection of raw milk products. Methods and results: Samples of bovine ( n = 220) and caprine ( n = 213) bulk milk, and raw milk products ( n = 82) were analysed for S. aureus. Isolates were tested for staphylococcal enterotoxin ( SE) production ( SEASED) by reversed passive latex agglutination and for SE genes ( sea - see, seg - sej) by multiplex PCR. Staphylococcus aureus was detected in 165 ( 75%) bovine and 205 ( 96.2%) caprine bulk milk samples and in 31 ( 37.8%) raw milk product samples. Enterotoxin production was observed in 22.1% and 57.3% of S. aureus isolates from bovine and caprine bulk milk, respectively, while SE genes were detected in 52.5% of the bovine and 55.8% of the caprine bulk milk isolates. SEC and sec were most commonly detected. A greater diversity of SE genes were observed in bovine vs caprine isolates. Conclusions: Staphylococcus aureus seems highly prevalent in Norwegian bulk milk and isolates frequently produce SEs and contain SE genes. Enterotoxigenic S. aureus were also found in raw milk products. Significance and Impact of the Study: Staphylococcus aureus in Norwegian bovine and caprine bulk milk may constitute a risk with respect to staphylococcal food poisoning from raw milk products.