Streptococcus agalactiae virulence factors isolated from bovine mastitis and antibiotic treatment response.

Aims: This study aims to characterize the virulence factors of Streptococcus agalactiae strains isolated from bovine mastitis and their potential association with the antibiotic treatment response.

Methods And Results: Four different profiles were identified among the 181 S. agalactiae strains using polymerase chain reaction, of which hyl B and cylE were found in 100% of the isolated strains, followed by cfb (99.5%), scpB (40.3%), and lmb (15.5%). The cell invasion assay showed that lmb-positive strains exhibited higher invasion ability than lmb-negative. There was a significant association (P = 0.018) between lmb gene and cows that required more than one treatment cycle.

Conclusions: These results showed that intramammary infections caused by lmb-carrier S. agalactiae strains did not adequately respond to the antibiotics administered, likely because of the presence of this virulence factor, which potentially favours the cell invasion capacity of these strains.