Virulence Potential and Antibiotic Resistance of Staphylococcus aureus Isolates from Clinical, Colonizing and Environmental Sources

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Abstract
Introduction: Staphylococcus aureus (S. aureus) is a facultative anaerobe commonly colonizing the nose, skin and other sites. It causes localized and systemic infections, is a major agent of hospital-acquired disease and methicillin resistance complicates treatment. We analyzed isolates from patients, healthy carriers and environmental sources. Materials and methods: A total of 100 S. aureus isolates were analyzed, comprising 50 clinical, 40 colonizing and 10 environmental samples. The study assessed antibiotic resistance profiles, virulence determinants and the presence of associated genetic markers. Results: Based on cefoxitin resistance testing, 46 isolates were classified as methicillin-resistant S. aureus (MRSA) and 54 as methicillin-susceptible S. aureus (MSSA). The mecA gene was detected in 36 (78%) MRSA isolates and, unexpectedly, in 27 (50%) MSSA isolates. Among clinical isolates, 22/50 (44%) were positive for Panton-Valentine Leukocidin (PVL), 34/50 (68%) for α-hemolysin (Hla), 44/50 (88%) for fibronectin-binding protein A (FnbA) and 43/50 (86%) for staphylococcal protein A (SpA) genes. In colonising isolates, the prevalence was lower for PVL (8/40, 20%), Hla (14/40, 35%) and SpA (25/40, 62.5%). However, FnbA showed a higher frequency of 39/40 (97.5%). Environmental isolates showed lower rates, with PVL present in 1/10 (10%), Hla in 5/10 (50%), FnbA in 9/10 (90%) and SpA in 2/10 (20%). Conclusion: MRSA isolates exhibiting virulence properties that are frequently encountered in hospital settings pose significant therapeutic challenges, contributing to increased morbidity and mortality. Effective infection control and robust surveillance strategies are essential to monitor and limit their transmission. Furthermore, restricting the availability of over-the-counter antibiotics is critical to curbing the spread of MRSA and may aid in its long-term control, if not eradication.

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