Coexistence of the blaZ gene and selected virulence determinants in multidrug-resistant Staphylococcus aureus: insights from three Nigerian tertiary hospitals.

Background And Purpose: Infections caused by β-lactamase-producing strains of Staphylococcus aureus have become increasingly difficult to treat due to the expression of multiple virulence factors. This has heightened concerns about managing S. aureus-related infections. This study was conducted to characterize the blaZ gene and selected virulence determinants in β-lactam resistant S. aureus from human sources in three Nigerian tertiary hospitals.

Materials And Methods: Three hundred and sixty samples were collected for the study. S. aureus was isolated and characterized following standard microbiological protocols and nuc gene amplification. Antibiotic susceptibility and minimum inhibitory concentration tests were performed using the disk diffusion method and E-tests, respectively. Biofilm formation and β-lactamase production were assessed using Congo red agar and nitrocefin kits, while the blaZ gene was examined using conventional PCR. Capsular polysaccharide genotyping, accessory gene regulator (agr) detection, Panton-valentine leucocidin (PVL), and PVL proteins were performed using PCR and Western blotting.

Results: S. aureus was recovered from 145 samples, 50 (34.5%) of these isolates exhibited multidrug resistance, with MICs ranging from 0.125 to 1.00 µg/mL, and showed significant resistance to aminoglycosides, fluoroquinolones, and β-lactams. Of these, 31 strains produced β-lactamases, 30 of which carried the blaZ gene in combination with cap8 (80%) or cap5 (20%). Biofilm formation and PVL gene were observed in 85% of the 20 randomly selected blaZ-positive multidrug-resistant (MDR) strains. The agr2 allele was predominant, found in 70% of the selected MDR strains. No significant difference in the occurrence of the blaZ gene was found among the three clinical sources (p ≤ α0.05).

Conclusion: The co-occurrence of the blaZ gene with PVL, capsular polysaccharide genes, and agr alleles is associated with biofilm formation, indicating a high risk of β-lactam-resistant S. aureus infections. Our findings highlight the need for continuous molecular surveillance to enhance infection management, treatment options, and patient outcomes in the study locality. A limitation of this study is the random selection of MDR isolates, which may affect the comprehensiveness of the analyses.