Virulence factors and antimicrobial resistance of Staphylococcus aureus isolated from bovine mastitis in Rio de Janeiro

Coelho S. M. O., Reinoso E., Pereira I. A., Soares L. C., Demo M., Bogni C & Souza M. M. S. 2009. Virulence factors and antimicrobial resistance in Staphylococcus aureus isolated from bovine mastitis in Rio de Janeiro. Pesquisa Veterinaria Brasileira 29(5): 369-374. Departamento de Microbiologia e Imunologia Veterinaria, Instituto de Veterinaria, Universidade Federal Rural do Rio de Janeiro, Seropedica, RJ 23890-000, Brazil. E-mail: miliane@ufrrj.br The study was conducted to characterize pheno-genotypically the virulence factors and resistance pattern of Staphylococcus aureus isolates from milk samples of cows with subclinical mastitis. All hemolytic isolates presented beta-hemolysin, and 38% of the nonhemolytic isolates were able to express hemolysins in the presence of a beta-hemolytic strain. The amplification of the coa-gene displayed four different size polymorphisms with about 400 bp, 600 bp, 700 bp and 900 bp. The spaA gene that encodes the IgG-binding region of protein A revealed sizes of 700 bp and 900 bp. The amplification of region X from spaA yielded a single amplicon for each isolate with the prevalent amplicon size being of 180 bp. Amplification of sae gene yielded an amplicon size of 920 bp in 71% of the isolates. Antibiotic resistance pattern revealed that 42% S. aureus were susceptible to all antimicrobials tested. Seven different antibiotic patterns were observed. Our results indicated that 47% and 25% of S. aureus strains exhibited resistance to penicillin and oxacillin respectively. All oxacillin-resistant isolates were mecA-positive.