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Abstract
This study investigated the virulence and genotypic profiles of S. aureus causing bovine subclinical mastitis (SCM) and their relatedness to the isolates from Kareish cheese. The isolates of coagulase-negative staphylococci (CNS) were also differentiated and characterized. One hundred and fifty California Mastitis Test-positive quarter milk samples were aseptically obtained from household cows and buffalos, as well as 75 samples of raw skim milk soft cheese (Kareish cheese) were collected from the same district of milk sampling. from SCM and Kareish cheese samples, 26 S. aureus isolates were identified. In addition, 76 isolates were characterized as CNS. Amongst 16 different CNS species, S. epidermidis and S. warneri were the most prevalent in SCM and Kareish cheese samples, respectively. The antibiogram revealed high rate of multidrug resistance in S. aureus and S. epidermidis isolates. Whereas the resistance to β-lactams was the most predominant. Sixteen methicillin-resistant S. aureus (MRSA) and 22 methicillin-resistant CNS (MRCNS) were revealed. Furthermore, testing of staphylococcal enterotoxins production, Staphylococcus Cassette chromosome mec (SCCmec) classification, Staphylococcal protein A (spa) typing, and detection of the genes encoding staphylococcal enterotoxins (SEs), species-specific leukocidin (pvl, lukM), and antimicrobial resistance genes were performed. While MRCNS isolates were characterized for SCCmec and tested for SEs production. Spa typing revealed 20 genotypes in 26 S. aureus strains, whereas similarities between SCM and cheese genotypes was revealed. However, these isolates showed heterogenicity in their virulence traits. Notably, a new spa type ‘t18546’ of a cheese strain was reported in this study. The high occurrence of human-specific virulence markers in the S. aureus strains from SCM and cheese, indicates the human as a potential source of such strains. One the other hand, enterotoxigenic S. epidermidis and S. warneri strains were detected. Additionally, the antibacterial effect of green tea extract, epigallocatechin 3-gallate (EGCg), was tested against an enterotoxigenic MRSA strain identified in this study. The concentration of 500 mg/L of EGCg showed the most inhibitory effect on the growth of CM179 strain. However, the concentration of 125 mg/L displayed a consistent downregulation of the transcription of enterotoxin genes sea and seh at different time intervals. In the conditions of household dairy production, the emergence of virulent MDR staphylococcal strains is potential and can constitute public health threat.
Keywords: Staphylococcus species; subclinical mastitis; Cheese, Virulence; Biocontrol.