Aims:Staphylococcus aureus is an important pathogen characterised by its potential to express many virulence factors. Currently, special attention is being paid to methicillin-resistant strains of S. aureus (MRSA). The aim of this study was to compare the prevalence of 13 selected virulence factor genes in methicillin-resistant versus methicillinsusceptible S. aureus (MSSA) isolates and to investigate their accumulation in the same isolate.Methods: Real-time PCR was used to detect the presence of genes in 200 isolates of S. aureus (100 MRSA and 100 MSSA) from the University Hospital Olomouc collected in [2005][2006].Results: Six out of the 13 monitored genes were detected more frequently in MRSA isolates: sea, seb, seg, sei, sej and eta, coding for the production of the enterotoxins A, B, G, I, J and the exfoliative toxin A. On the other hand, the pvl and tst genes coding for Panton-Valentine leukocidin and TSST-1 were more frequent in MSSA. Statistical analysis (chi-squared test) of the prevalence of virulence factors in the two groups showed a significant difference (P<0.05) in two cases (seg, sei).Conclusions: A higher prevalence of selected virulence genes was not confirmed in the methicillin-resistant S. aureus group. This indicates no further increase in their threat.

A rather fast and complicated progression of an infection caused by some strains of Staphylococcus aureus could be associated with the expression and co-action of virulence factor complexes in these strains. This study screened the antibiotic susceptibility and prevalence of virulence markers in isolates of meticillin-resistant S. aureus (MRSA) obtained from patients hospitalized at the University Hospital in Olomouc, Czech Republic. A total of 100 isolates was screened for 13 genes encoding extracellular virulence determinants (tst, pvl, eta, etb, sea, seb, sec, sed, see, seg, seh, sei and sej) and for their distribution in sample types. Eighty-nine isolates were positive for at least one of the genes. Genes for etb, pvl, see and seh were not detected in any of the MRSA isolates. No statistically significant differences in the occurrence of the determinants studied among sample types were found. INTRODUCTIONStaphylococcus aureus is one of the major nosocomial pathogens. Particular attention should be paid to meticillin-resistant S. aureus (MRSA). Resistance to meticillin is determined by the presence of the mecA gene encoding penicillin-binding protein with very low affinity to blactam antibiotics (Chambers, 1997). S. aureus produces a broad spectrum of extracellular and cell wall-associated virulence determinants (Foster, 2002). Among them, a wide variety of surface adhesins known as microbial surface components recognizing adhesive matrix molecules (MSCRAMMs) has been described (Patti et al., 1994).The most common staphylococcal proteins anchored in the cell wall are proteins with affinity to fibrinogen (i.e. clumping factors A and B, encoded by the clfA and clfB genes, respectively), fibronectin (fnbA), collagen (cna), sialoprotein (bbp), elastin (ebpS) and adhesins with unknown function (sdrC and sdrE) (Jonsson et al., 1991;Josefsson et al., 1998; McDevitt et al., 1997;Ní Eidhin et al., 1998; Park et al., 1996;Speziale et al., 1986;Tung et al., 2000). The second group of virulence factors is represented by a family of bacterial proteins with superantigen activity: enterotoxins A-E, G-R and U (encoded by the genes seasee, seg-ser and seu), toxic shock syndrome toxin-1 (TSST-1, encoded by tst), exfoliative toxins A and B (eta and etb) and other toxins such as a-, b-, c-and d-toxin and the Panton-Valentine leukocidin (pvl) (Arbuthnott et al., 1982;Bhakdi & Tranum-Jensen, 1991;Bohach et al., 1990;Prevost et al., 1995).Apart from syndromes caused by toxin production, S. aureus pathogenesis results from synergistic interactions of a variety of the above-mentioned factors. Exfoliative toxin and pyrogenic toxin superantigen production enables S. aureus to cause staphylococcal scalded skin syndrome (SSSS), staphylococcal toxic shock syndrome and staphylococcal food poisoning. Experimental models indicate that the expression of receptors for fibrinogen and fibronectin is associated with endocarditis, whereas the presence of adhesins for sialoprotein, collagen and fibronectin is associated with arthritis and osteomyel...