gene sequence analysis can prevent misidentification of coagulase-negative strains and contribute to their control in dairy cow herds.

Accurate and precise differentiation of staphylococci isolated from milk is of importance for udder health management. In particular, the rapid and specific identification of plays an essential role in the prevention and treatment programs for bovine mastitis. Plasma gelatinization in coagulase assays is routinely used to discriminate from other species by detecting the presence of extracellular free staphylocoagulase. However, rarely occurring coagulase-deficient strains can be responsible for clinical and subclinical mastitis cases. By investigating isolates from a single herd over a 10-year period we identified the persistence of a phenotypically coagulase-negative strain and pinpointed the possible cause to a single base pair deletion in the gene sequence. Our results support the need to integrate primary biochemical tests with molecular/sequence analysis approaches for correctly identifying and discriminating atypical in bovine herds, as the coagulase test alone may fail to detect persistent mastitis-causing strains.