Biofilm formation of Staphylococcus aureus from milk and expression of the adhesion genes ebpS and cna at different temperatures

Abstract

This study investigated the ability of Staphylococcus aureus isolates from milk to form biofilm, through detection of adhesion genes, investigating exopolysaccharide (EPS) production and biofilm formation on polystyrene (PS) and stainless steel (SS) surfaces, and by quantifying the expression of ebpS and cna genes under different temperatures and culture media. Among the 31 isolates, the adhesion genes ebpS and cna were found in 81% and 61% of the isolates, respectively. The screening tests for phenotype revealed that 58% of the isolates were EPS producers, and 45% showed the ability to produce biofilm on PS. Nine of the 31 isolates were selected to verify their ability to form biofilm on SS, of which 3 were non-biofilm producers, 3 were poor biofilm producers, and 3 were moderate biofilm producers. However, all nine isolates produced biofilm on SS, regardless of their phenotypic profile on PS. Reverse-transcriptase quantitative PCR (RT–qPCR) revealed no variation in the expression levels of ebpS and cna genes at different temperatures, except for isolate S24 at 10 °C, for both genes tested. Moreover, RT–qPCR assays revealed that the expression levels of the adhesion genes ebpS and cna are isolate- and temperature-dependent; however, they are independent of the phenotypic biofilm-formation profile.