Prophage- and pathogenicity islands-associated virulence genes in Staphylococcus aureus isolated from patients at Srinagarind Hospital, Khon Kaen

Abstract

Staphylococcus aureus, a well-known human pathogen, causes a variety of infections in human, e.g. superficial skin infection through life-threatening infection. S. aureus is able to produce many enzymes, including exotoxins which lead to tissue inflammation and injury. Moreover, it also plays an importance role in clinical practice by exhibiting resistance phenotype to methicillin. Many virulence determinants are located on mobile genetic elements (MGEs), such as bacteriophages, pathogenicity islands (PAI), and genomic islands, and existed variably in the bacterial population. Then, virulence genes can be used as genetic markers for clinical manipulations, and nosocomial control measurement. The objective of this study was to determine virulence genes associated with those MGEs in S. aureus samples both in methicillin-susceptible S. aureus (MSSA), and methicillin-resistant S. aureus (MRSA). A total of 100 MSSA and MRSA isolates (50 of each) were randomly selected from clinical samples of patients at Srinagarind Hospital during November, 2006 through June, 2007. All isolates were determined for the presence of eta, lukDE, lukSF-PV, tst-1, sak, sea, sec, sel, and sep genes by PCR. In case of MRSA, staphylococcal cassette chromosme mec (SCCmec) types were also determined in order to study the association among the determinants and their allotypes. The results showed that most of S. aureus samples harbored at least one virulence gene, and most of them carried lukDE (90 %), and sak (88 %). High potential virulence genes, eta and lukSF-PV, were detected in 2 and 10 isolates of MSSA only. However, sea gene was detected more frequent in MRSA than MSSA (P < 0.05). While sec gene was significantly recognized less in MRSA than MSSA isolates (P < 0.05). The other staphylococcal enterotoxins such as sec, sel and sep were detected in small samples of S. aureus, and none was found to harbor tst-1 gene. The molecular information associated to virulence genes on MGEs may be useful in clinical practice and hospital epidemiology in Srinagarind Hospital, and other tertiary care facilities.