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

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.

Discriminatory powers of molecular typing techniques for methicillin-resistant Staphylococcus aureus in a university hospital, Thailand.

Discriminatory powers of various molecular techniques were evaluated for typing of methicillin-resistant Staphylococcus aureus (MRSA) isolated in Siriraj Hospital, Bangkok, Thailand. Thirty MRSA isolates were randomly selected in this study. They were characterized by pulsed-field gel electrophoresis, Clal-mecA and Clal-Tn554 polymorphisms, ribotyping, and PCR-based methods including SCCmec typing, spa and coa gene polymorphism, and repeat units in hypervariable region downstream of mecA. Individual molecular typing technique distinguished those MRSA isolates into 2 to 5 types. Eleven genetic backgrounds of MRSA isolates were elucidated by combination of typing methods with trimethoprim/sulfamethoxazole (TMP/SXT) susceptibility. Combination of all typing methods including TMP/SXT susceptibility yielded a discriminatory index of 0.94. Combination of PCR-based methods and TMP/SXT susceptibility, with the discriminatory index of 0.89, is a practical typing approach suitable for rapid epidemiological investigation of MRSA isolates in a hospital setting.