Virulence gene profile and biofilm formation ability of Staphylococcus isolated from clinical and subclinical bovine mastitis in Bihar

Mastitis is the one of the most prevalent and costly disease of dairy industry. Mastitis is multi etiological and complex in nature. Among bacterial mastitis, Staphylococcal mastitis is the predominant type. Pathogenic potential of Staphylococcus depends on the numbers and combination of virulence genes and also on the geographical distribution. This study was conducted in order to screen and identify the major virulence factors of coagulase positive and coagulase negative Staphylococcus, isolated from clinical and subclinical bovine mastitis milk samples collected from Bihar state of India so that they could act as immunogenic target for vaccine development. Genomic DNA was isolated from the staphylococcal isolates and was screened by PCR for the presence of genes associated with biofilm formation (bap, icaA and icaD); genes encoding microbial surface components recognizing adhesive matrix molecules (IJSCRAMIls; cna, ebpS, eno, fib, fnbA, fnbB, clfA and clfB) and tsst1 encoding superantigenic toxin. All the isolates were found positive for eno (100%) followed by clfA and fib in 84%; fnbA and tsst-1 in 60%, clfB (52%), cna (44%), fnbB (40%), ebps (16%), bap (16%), icaA(10%) and icaD (8%) of the isolates. Biofilm formation ability of the isolates was also tested by microtiter plate method. 66% of the isolates were found to be biofilm producers with different production level. Out of the biofilm positive isolates, 10% were strong, 32% moderate and 24% were weak biofilm formers whereas 34% of isolates did not form biofilm. The most prevalent virulence factors were thus identified as eno, clfA, fib and tsst-1 which could be used as potential immunogenic target for vaccine development against staphylococcal mastitis.