Comparison of Virulence, Resistance Genes, and SCCmec Types in CoNS and Staphylococcus aureus Strains Isolated from Raw Cow Milk Samples

Abstract

Although there has been extensive research on the presence of Staphylococcus aureus (S. aureus) in raw milk samples, new data on the prevalence and molecular characterization of Coagulase-negative Staphylococci (CoNS) are needed. This study aimed to compare the antimicrobial profiles, virulence genes, and SCCmec types distribution between S. aureus and CoNS isolated from one hundred and fifty raw cow milk samples in Istanbul. Staphylococcus isolates were identified using VITEK MS following classical culture methods. Phenotypic antibiotic susceptibility was determined using the disc diffusion method. In-house PCR was employed to detect resistance genes, while multiplex PCR and qPCR were utilized for SCCmec typing and virulence genes such as SEs, respectively. Out of the seventy-five contaminated samples (50%), 32% harbored S. aureus, and 68% were CoNS. Methicillin resistance was identified in 10.6% of S. aureus and 14.6% of CoNS. SCCmec type IV predominated in both MRSA (50%) and MRCoNS (54.5%). At least one toxin gene was present in 83.3% of S. aureus and 22.4% of CoNS isolates, with sei being the most frequently observed. None of the S. aureus isolates tested positive for the sed, see, and pvl genes. Similarly, the sea, sed, see, tsst-1, and pvl genes were not detected in any of the CoNS isolates. As a conclusion, SCCmec type IV and sei gene predominated and community-acquired resistance patterns were prominent in Staphylococcus strains, which carried various virulence and resistance genes. Beyond MRSA, the presence of MRCoNS should be considered and monitored as a significant public health concern in raw milk. © 2025 Elsevier B.V., All rights reserved.