Bovine mastitis: The diagnostic properties of a PCR-based assay to monitor the Staphylococcus aureus genotype B status of a herd, using bulk tank milk

Abstract

Staphylococcus aureus genotype B (GTB) is a contagious mastitis pathogen in cattle, occurring in up to 87% of individuals. Because treatment is generally insufficient, culling is often required, leading to large economic loss in the Swiss dairy industry. As the detection of this pathogen in bulk tank milk (BTM) would greatly facilitate its control, a novel real-time quantitative PCR-based assay for BTM has previously been developed and is now being evaluated for its diagnostic properties at the herd level. Herds were initially classified as to their Staph. aureus GTB status by a reference method. Using BTM and herd pools of single-quarter and 4-quarter milk, the herds were then grouped by the novel assay, and the resulting classifications were compared. A total of 54 dairy herds were evaluated. Using the reference method, 21 herds were found to be GTB positive, whereas 33 were found to be negative. Considering the novel assay using both herd pools, all herds were grouped correctly, resulting in maximal diagnostic sensitivities (100%) and specificities (100%). For BTM samples, diagnostic sensitivities and specificities were 90 and 100%, respectively. Two herds were false negative in BTM, because cows with clinical signs of mastitis were not milked into the tank. Besides its excellent diagnostic properties, the assay is characterized by its low detection level, high efficiency, and its suitability for automation. Using the novel knowledge and assay, eradication of Staph. aureus GTB from a dairy herd may be considered as a realistic goal.

Clinical outcomes and molecular genotyping of Staphylococcus aureus isolated from milk samples of dairy primiparous Mediterranean buffaloes (Bubalus bubalis)

“…aureus GTB from milk samples of dairy primiparous Mediterranean buffaloes was described. Its contagiousness and ability to produce within-herd problems, as well as its virulence due to its gene patterns (enterotoxin genes A and D and polymorphic leucotoxin E gene), were widely described not only in Swiss dairy herds (Fournier et al, 2008;Syring et al, 2012) but also in dairy cows of several European countries (Cosandey and Graber, 2013).…”

“…The nuc gene is highly specific for Staph. aureus (Brakstad et al, 1992;Graber et al, 2007) and may, therefore, be used for definitive identification of suspicious colonies (Syring et al, 2012).…”

“…The lysates were then diluted 1:100 in H 2 O and served as templates for the different types of PCR. The PCR for the nuc gene was performed according to (Syring et al, 2012). Isolates lacking this gene were excluded from the present study.…”

“…For interpretation of the 16S-23S rRNA intergenic spacer region results, 2 patterns (genotypes) were considered different if 2 and more peaks of the electropherogram differed in size. To identify the genotypes, a recently developed in-house computer program was applied (Syring et al, 2012).…”

Bovine Staphylococcus aureus: Subtyping, evolution, and zoonotic transfer

“…In brief, all strains were first analyzed by melting curve PCR for nuc as described by Syring et al (2012). The nuc gene is highly specific for Staph.…”