Prevalence and Characterization of PVL-Positive Staphylococcus aureus Isolated from Raw Cow’s Milk

Abstract

The present study aimed to investigate the prevalence, antibiotic susceptibility profiles, and some toxin genes of Panton-Valentine leukocidin (PVL)-positive <i>Staphylococcus aureus</i> (<i>S. aureus</i>) in unpasteurized raw cow's milk collected from retail outlets located at Mansoura, Dakahliya governorate, Egypt. In that context, a total of 700 raw cow's milk samples were investigated for the presence of <i>S. aureus</i>, which was identified in 41.1% (288/700) of the samples. Among the <i>S. aureus</i> isolates, 113 PVL-positive <i>S. aureus</i> were identified and subjected for further analysis. The PVL-positive <i>S. aureus</i> were investigated for the existence of toxin-related genes, including hemolysin (<i>hla</i>), toxic shock syndrome toxin-1 (<i>tst</i>), and enterotoxins (<i>sea</i>, <i>seb</i>, <i>sec</i>, <i>see</i>, <i>seg</i>, <i>sei</i>, and <i>selj</i>). Genotypic resistance of PVL-positive strains was performed for the detection of <i>blaZ</i> and <i>mecA</i> genes. Among the PVL-positive <i>S. aureus</i>, <i>sea</i>, <i>seb</i>, and <i>sec</i> were detected in 44.2, 6.2%, and 0.9%, respectively, while the <i>hla</i> and <i>tst</i> genes were identified in 54.9% and 0.9%, respectively. The <i>blaZ</i> and <i>mecA</i> genes were successfully identified in 84.9 (96/113) and 32.7% (37/113) of the total evaluated <i>S. aureus</i> isolates, respectively. PVL-positive <i>S. aureus</i> displayed a high level of resistance to penicillin, ampicillin, and trimethoprim-sulfamethoxazole. Multidrug resistance (resistant to ≥3 antimicrobial classes) was displayed by all methicillin-resistant <i>S. aureus</i> (MRSA) and 38.2% of methicillin-sensitive <i>S. aureus</i> (MSSA) isolates. The obtained findings are raising the alarm of virulent PVL-positive MRSA clones in retail milk in Egypt, suggesting the requirement for limiting the use of β-lactam drugs in food-producing animals and the importance of implementing strong hygiene procedures in dairy farms and processing plants.