Molecular characterization and virulence factor profiles of Staphylococcus aureus isolated from bovine mastitis in Brazilian herds

Abstract

Staphylococcus aureus is the main etiological agent of bovine mastitis worldwide and knowledge about its diversity and virulence factors is vital in controlling infections caused by this pathogen. The present study aimed to perform molecular characterization of a population of S. aureus (n=153 strains isolated from 1994 to 2014 in seven Brazilian states) by pulsed-field gel electrophoresis (PFGE) and evaluate their virulence profiles via polymerase chain reaction (PCR). PFGE identified 93 pulsotypes, with the isolates organized into 26 clusters and 20 unique pulsotypes. Predominant pulsotypes were observed, with variations according to the years of isolation and geographic origin of the isolates. Based on the PCR results for the genes encoding agglutination factors (ClfA and ClfB), binding proteins (fibronectin binding protein - FnBPA, elastin binding protein - Ebps, collagen binding protein - Cna), and toxins (Hla, Hlb and Luk-ED), 40 virulence profiles were detected. The frequency of virulence genes ranged from 58 to 98% (clfA:84.3%; clfB and hlb both 81%; hla:71.2%; fnBA:82.3%; Can:94.7%; ebps:58%; and lukED:98%). The existence of prevalent genotypes in some of the Brazilian states and the time period studied suggests that these genotypes are better adapted, with favorable characteristics in host/pathogen relationships. Genes of proven importance for S. aureus pathogenesis in bovine mastitis were widely distributed in genetically divergent populations, suggesting that most of these genes may be interesting candidates in the development of vaccines to control bovine mastitis in Brazil.