[Investigation of the virulence genes in methicillin-resistant Staphylococcus aureus strains isolated from biomaterial surfaces]

Abstract

Staphylococci are the most important agents of nosocomial infections originating from biomaterials. The aim of this study was to investigate the presence of virulence genes and their phenotypic expressions in 11 methicillin-resistant Staphylococcus aureus strains isolated from the surfaces of clinically used biomaterials of 48 thorasic intensive-care unit patients. By the use of specific primers, the presence of genes encoding the attachment and biofilm production (icaA, icaC, bap), methicillin resistance (mecA), enterotoxins A-E (sea, seb, sec, sed, see), toxic shock syndrome toxin (tst), exfoliative toxins A and B (eta and etb), alpha- and beta-hemolysins (hla and hlb), staphylococcal exotoxin-like protein-1 (set1), proteases (sspA, sspB, aur, serine proteaz gene), lipase (geh) and the regulatory genes (sarA and agrCA) were investigated by polymerase chain reaction (PCR). The phenotypic properties of the isolates such as biofilm formation, antibiotic susceptibility, extracellular protease and lipase production were also evaluated. None of the isolates were found to be biofilm and/or slime producers, however, all strains were found to have icaA gene which is responsible for biofilm formation. Nevertheless the presence of icaC and bap genes that are also responsible for biofilm formation were not detected. All the strains have had mecA gene and were resistant to oxacillin, penicilin G and gentamicin, while 10 were also resistant to erythromycin and nine were also resistant to ofloxacin. The isolates were susceptible to vancomycin, teicoplanin and co-trimoxazole. Screening of toxin and regulatory genes revealed that all the strains harboured sea, set1, hla, hlb and sarA genes. The phenotypic tests for the determination of extracellular protease production revealed that all the strains formed very weak zones on skim milk and milk agar plates, and yielded negative results on casein agar plates. Furthermore, all strains were found to harbour sspA, sspB, aur and serine protease genes. Tween 20, Tween 80 and tributyrin containing media were used to detect lipase production and all strains gave late-positive results (on the third day of incubation), although they all lacked for lipase gene (geh). As a result, S. aureus strains isolated from biomaterial surfaces yielded positivity for some of the tested virulence genes, of which some of them have not been expressed phenotypically. Although there were some limitations in the study, it could be concluded that the presence of these virulence genes in S. aureus strains might be considered as potential threats especially in intensive care unit patients.