Isolation and Characterization of Staphylococcus aureus from Raw Cow's Milk and Investigating the Effect of Bifidobacterium bifidum Probiotic Cell Free Supernatant on Their Enterotoxins Genes Expression

The present reserach aimed to detect and isolate the genes involved in the staphylococcal enterotoxins (SEs) production in strains isolated from unprocessed cow’s milk and to examine the impact of Bifidobacterium bifidum probiotic cell-free supernatant (CFS) on their expression. Standard techniques were used for isolation and identification of Staphylococci strains in unprocessed milk. The PCR was used to identify strains carrying enterotoxin genes. The B. bifidum CFS was applied to strains containing the target genes, and the genes expression levels were quantified using Real-time PCR. Using ۱۶SrDNA sequencing, the phylogenic relationship of the isolated strains was determined. Analysis revealed that bacteria such as Staphylococcus species were found in the ۷۲% of the samples. The PCR test showed the presence of various SE superantigens, including SEA (۱۶.۷%), SEC (۱۱.۷%), SED (۸.۳%), SEE (۶.۷%), and SEB (۱.۷%) in isolated strains. The B. bifidum CFS had obvious antimicrobial activity against strains ۲۴, ۵۱, ۵۴, and ۳۵ of Staphylococcus species, and the minimum inhibitory concentration and minimum bactericidal concentration values for these strains treated with B. bifidum CFS were in the range of ۳۱.۲۵-۱۲۵ μg/ml. Strains ۵۱ and ۲۴ were clustered with S.aureus ATCC ۲۵۹۲۳, and strains ۵۴ and ۳۵ were clustered with S.aureus ATCC ۱۲۶۰۰, respectively. The RT-PCR exhibited that probiotics CFS suppressed the expression of SEA, SEB, SEC, and SEE genes (P<۰.۰۵). The average fold change for SEA, SEB, SEC, and SED genes was -۱.۶۸۱, -۱.۲۸, -۱.۵۲, and -۰.۸۴, respectively. The research demonstrated that probiotic bacteria can lower enterotoxin production by downregulating the expression of SEs genes.

Keywords:

Bifidobacterium bifidum , enterotoxin , Staphylococcus aureus