Staphylococcus aureus is one of the most common pathogens responsible for contagious bovine mastitis. Genes involved in biofilm formation is a special defensive mechanism of this pathogen to combat the host immune response and remain stable in hostile environment. The present study was designed with objectives to investigate strategies involving biofilm formation and biofilm associated genes (BAGs) of S. aureus strains, and to assess the consistency of two phenotype test methods. One hundred and two S. aureus strains were isolated from bovine subclinical mastitis cases from 32 commercial dairy farms in nine provinces of China. These isolates were screened for biofilm-producing capacity by Congo Red Agar (CRA) and Semi Quantitative Adherence Assay (SQAA) methods. Thirteen BAGs including rbf, SigB, SasG, icaA, sarA, icaR, icaD, clfA, clfB, fib, fnbpB, bap and fnbpA were amplified by PCR assay. The results of current study revealed that rbf (95.1%) and SigB (94.1%) were the most prevalent BAGs, followed by SasG (89.2%), icaA (88.2%), sarA (87.3%), icaR (84.3%), icaD (82.5%), clfA (64.7%), clfB (45.1%), fib (43.1%) and fnbpB (19.6%). However, bap and fnbpA genes were not detected in any strain. By CRA method, 78.4% strains of S. aureus produced biofilm and 48.0% of strains were biofilm-positive by SQAA. Therefore, the data concluded that majority of S. aureus strains were capable to produce biofilm, controlled by eleven associated genes, and CRA detection rate was higher than SQAA for biofilm producing capacity of S. aureus.

Key words: Biofilm, Biofilm-associated genes, Bovine mastitis, Staphylococcus aureus, Subclinical mastitis