Biofilm production, antibiotic resistance and the presence of ica, bap, agr and blaz genes in bovine mastitis-associated Staphylococcus aureus isolates from Karnataka

Biofilm formation is an important virulence determinant of Staphylococcus aureus which is a major etiological agent of bovine mastitis. Here, 132 bovine mastitis-associated S. aureus were subjected to biofilm production, antimicrobial susceptibility, and the detection of ica, bap, agr and blaZ genes. It was found that 33.3% of the isolates produced biofilm. The number of isolates resistant to individual antibiotics increased by 1.2- to 7.0-fold when growing in biofilm versus planktonic mode of growth, and the spectrum of antibiotics as well as the number of isolates resistant to various antibiotics increased with the increase in the density of the biofilm. However, there was no correlation between the strength of biofilm and the extent of antibiotic resistance. When evaluated for the presence of genes reported to be associated with biofilm formation, bap gene was detected in a significant number (12.9%) of the isolates, while the ica locus was equally distributed among strains that produced biofilm or not. A significant correlation was observed between the presence of agrI and ica genes. High blaZ positivity was observed irrespective of penicillin resistance or biofilm phenotype. In summary, biofilm forming S. aureus was more resistant to many antibiotics in biofilm than in planktonic form, and none of the genes studied showed association with phenotypic studies of either biofilm production or antimicrobial susceptibility. The study highlights the need for further investigations on the inter-relationships between biofilm, antibiotic resistance and associated genotypes.