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

Automated summary

Accurate and precise differentiation of staphylococci isolated from milk is crucial for managing udder health, especially the rapid and specific identification of Staphylococcus aureus for preventing and treating bovine mastitis. However, rarely occurring coagulase-deficient S. aureus strains may cause clinical and subclinical mastitis cases. By studying S. aureus isolates from a single herd over 10 years, we found the persistence of a coagulase-negative S. aureus strain due to a single base pair deletion in the coa gene sequence. It highlights the importance of integrating biochemical and molecular/sequence analysis methods to correctly identify and discriminate atypical S. aureus strains in bovine herds.