Mastitis diagnostics: qPCR for Staphylococcus aureus genotype B in bulk tank milk

A novel real-time quantitative PCR assay for detecting the pathogenic and contagious Staphylococcus aureus genotype B (GTB) in bulk tank milk (BTM) was developed and evaluated. The detection of this pathogen in BTM would greatly facilitate its control as it is responsible for great economic loss in Swiss dairy herds. The assay is based on the simultaneous detection of 3 GTB-typical target sequences including 2 enterotoxin genes and a polymorphism within the leukotoxin E gene. A variety of mastitis-associated bacteria was used to validate the assay, resulting in an analytical specificity of 100%, and a high repeatability. The analytical sensitivity in milk was 40 cfu/ml corresponding to a calculated detection limit of 1 GTB-positive cow among 138 healthy ones using BTM. An exponential association between simulated cow prevalence and quantitative PCR result was observed. A first field study revealed 1 GTB-positive herd among the 33 studied herds. This novel assay for BTM analysis is suitable for routine purposes and is expected to be an effective tool for minimizing S. aureus GTB in Swiss dairy herds.