Accessory gene regulators and virulence genes associated with the pathogenicity of Staphylococcus aureus from clinical and community settings in Lagos, Nigeria

Abstract

Staphylococcus aureus is a prominent pathogen that causes serious community and hospital-acquired infections globally. Its pathogenicity is attributed to a variety of secreted and cell surface associated proteins that are modulated by the quorum-sensing accessory gene regulator (agr) system. In this study, we investigated the presence of toxin genes and agr involved with S. aureus from clinical samples and apparently healthy individuals. Unequivocal identification of the isolates was obtained with the Vitek 2 system. We screened 70  clinical (CL) and 22 community (C) S. aureus strains for the methicillin resistance (mecA) gene, agr and superantigens (SAg) (enterotoxins  and toxic shock syndrome toxin-1) using PCR techniques. A total of 12 clinical isolates were classified as methicillin-resistant S. aureus (MRSA); 89 isolates belonged to one of the four agr groups (agr1-4), and 3 isolates were non-typeable. Of the agr groups, agr1 was the  most prominent and mostly consisted of isolates from pus/wounds. The methicillin-susceptible S. aureus (MSSA) isolates were distributed  within the four agr groups while MRSA strains were restricted to agr1 and agr3 . The most common enterotoxin gene, sei,  was likewise more prevalent in MSSA strains than in MRSA strains, where sea predominated. The co-existence of two or more  enterotoxins was confirmed in 40% of the isolates. sea occurred through all the agr groups except agr3 and sei was not found in agr1 and  agr4 . The toxic shock toxin (tst) gene was detected in six MSSA. These findings suggest that MSSA may cause more lethal infections  than MRSA because of the increased frequency of toxic genotypes seen in MSSA strains.

Significance:

• Isolates in the agr^1,3 groups had  more SAg toxin genes, whereas isolates in the agr⁴ groups possessed more tst genes.

• The MSSA isolates contained higher proportions  of virulence genes than MRSA.

• The clinical implications of this discovery include that MSSA may cause more lethal infections than MRSA  due to the greater number of toxigenic genotypes discovered.