Analysis of Virulence Genes of Staphylococcus aureus, Streptococcus, E. coli Isolated from Bovine Subclinical Mastitis

Abstract

Background: The major mastitis-producing organisms are Staphylococcus aureus, Streptococcus agalactiae, Streptococcus dysgalactiae, Streptococcus uberis and Escherichia coli. Molecular characterization of the major bacterial pathogens for some genes responsible for their virulence should be considered the reduction of risk factors responsible for the presence and spread of contagious pathogens through milk. Methods: The two hundred milk samples were collected from cows and buffaloes of four different tehsils of the Sirohi district of Southern Rajasthan. Out of 200 milk samples, 74 milk samples that were found positive for SCM were cultured for primary isolation of predominant bacterial pathogens. Out of these 74 positive samples, total of 97 isolates were recovered from these milk samples either as a single or mixed infection. To genotypically characterize S. aureus isolates, genes encoding virulence determinants (spa-IgG-binding and Coa), Staphylococ cal enterotoxins (bac and bca) and E. coli Shiga toxins (stx1 and stx2) were investigated. Result: The etiological prevalence of SCM caused by different bacteria was, S. aureus, (27%), Streptococcus spp. (15%) and E. coli (6.5%) respectively either as single and or as mixed infections. All S. aureus isolates were tested by PCR for the presence of the spa gene and coa gene results revealed that 40 isolates (74.0%) carried both spa (IgG-binding) and coa gene. 11 isolates of S. agalactiae (36.6%) carried the bca gene. The bca gene codes for Alpha-C protein, a surface protein that helps the bacteria to enter the host cells. E. coli isolates were also screened for the presence of virulence gene stx1 and stx2 gene. Out of 13 isolates tested, 6 isolates harboured both stx1 and stx2 genes.