Association of virulence genes with mecA gene in Staphylococcus aureus isolates from Tertiary Hospitals in Nigeria

Staphylococcus aureus is the etiological agent for a wide range of human infections, and its pathogenicity largely depends on various virulence factors associated with adherence, evasion of the immune system and damage of the host. This study determined the prevalence of methicillin-resistant S. aureus (MRSA) and some selected virulence genes in clinical isolates of S. aureus from South-Western Nigeria. The antibiotic susceptibility of 156 S. aureus isolates to various antibiotics was determined. Moreover, polymerase chain reaction detection of the mecA gene was performed including SCCmec typing, and the isolates were screened for selected genes (alpha hemolysin [hla], intracellular adhesion A [icaA], Panton-Valentine leukocidin [PVL], fibronectin binding protein A [fnbA], bone sialoprotein binding protein [bbp], exfoliative toxin A [eta], exfoliative toxin B [etb], and collagen binding adhesion [cna]) associated with virulence. The prevalence of mecA gene was 42.3% (66 out of 156 S. aureus), and SCCmec typing showed that 24 (36.4%) carried the SCCmec II element, 4 (6.1%) with type III, 10 (15.2%) with SCCmec IV, and 28 (42.4%) harbored type V. The proportion of S. aureus with the following genes was ascertained: Hla (55.1%), icaA (42.3%), PVL (34.6%), fnbA (8.3%), bbp (4.5%), and eta (3.8%). All the isolates were etb and cna negative. The prevalence of the PVL gene in methicillin susceptible Staphylococcus aureus (MSSA) was 53.3% compared with 9.1% of MRSA. An association between virulence genes (eta and icaA) and mecA positive S. aureus; and significant difference in the distribution of virulence genes in in-patients and out-patients were found. The MRSA strains in South-Western Nigeria were dominated by SCCmec II and SCCmec V. The study concluded that there is a high prevalence of MRSA in Nigeria with association of eta and icaA genes with mecA gene in S. aureus isolates.