Molecular Detection of Genes Encoding Virulence Determinants in Staphylococcus aureus Strains Isolated from Bovine Mastitis

Abstract

4 Abstract: Staphylococcus aureus is often responsible for intramammary infections in bovines, and is the main etiological agent of contagious clinical/subclinical mastitis in dairy herds. The aim of this study aims at the genotypic characterization of S. aureus strains isolated from dairy cows suffering from mastitis in the Egyptian farms. A total of 68 S. aureus strains, obtained from 456 milk samples of 120 dairy cows from eight different farms in Delta, Egypt, were phenotypically characterized and identified. In addition, antibiotic resistance pattern of these strains was investigated. Amplification of genes encoding clumping factor (clfA), coagulase (coa), thermonuclease (nuc), enterotoxin A (entA), and the gene segments encoding the immunoglobulin G binding region and the X region of protein A gene spa by Polymerase Chain Reaction was used for the genotypic characterization of isolated S. aureus strains. All samples were negative for the presence of entA gene but yielded an amplicon size of about 985 bp in case of clfA gene. However, amplification of coa gene yielded DNA bands of three different sizes. Amplification of the polymorphic spa gene segment encoding the X-region of protein A was detected in 56 strains out of 68 (82.4%) whereas immunoglobulin G binding region was only observed in 22 strains (32.4%). Percentage was raised in case of thermonuclease gene, nuc where it was observed in 53 strains (78%). The data in this study provided an overview on the distribution of virulence determinants of S. aureus strains which contribute in bovine mastitis problem in the Egyptian farms.