Comparison of Three Methods for Routine Detection of Staphylococcus aureus Isolated from Bovine Mastitis

Summary The present study aimed to compare three identification methods that are routinely used for the detection of Staphylococcus aureus as bovine mastitis agent. The evaluated methods were as followed: conventional biochemical method, commercial identification system BioLog (Gen III MicroPlate) and amplification of species-specific gene (nuc) by polymerase chain reaction (PCR). A total of 73 staphylococcal isolates were collected from 453 individual milk samples from dairy cows with subclinical and clinical mastitis from different farms in Bulgaria. This isolates were determined as 60 coagulase-positive, 3 catalase-negative and 10 coagulase-negative by conventional methods. BioLog system identified 72 isolates as S. аureus subsp. aureus and one coagulase-positive isolate as S. schleiferi subsp. coagulans. PCR amplification of nuc gene further confirmed S. аureus subsp. aureus isolates identified by the BioLog system. The primary identification of S. aureus on the basis of coagulase level led to erroneous determination of 14 (19.2%) of the isolates. Based on the findings, BioLog system and PCR appear to be more reliable detection systems for S. aureus from milk. In conclusion, the present study showed that a routine approach using a combination of phenotypic and molecular detection systems could improve S. aureus detection in milk.