Detection of genes for superantigen toxins in methicillin-resistant Staphylococcus aureus clinical isolates in Karachi

To detect genes for enterotoxins, exfoliative and toxic shock syndrome toxins in Staphylococcus aureus (S. aureus) strains isolated from clinical specimens. Cross-sectional observational study. Department of Molecular Genetics, Dr. Ziauddin Hospital, Karachi, from January to December 2010. Two hundred and ninety eight S. aureus clinical isolates were obtained from various clinical samples received at Dr. Ziauddin Hospital, Karachi. Out of these, 115 were detected as methicillin resistant (MRSA) by cefoxitin disk diffusion test showing a prevalence rate of 38.6%. Detection of individual toxin genes was performed by Polymerase Chain Reaction (PCR) by using only one primer pair for each tube. Uniplex primers were preferred as multiplex primers are longer in base pairs and have the potential for cross reaction due to non-specific binding and increase in optimization time. The possession of a single gene or more than a single gene in MRSA isolates was found in 61.73% of clinical samples; the highest number was found in pus swab, followed by sputum, blood, urethral swab, and urine. The prevalence of toxin genes was higher in MRSA as compared to methicillin sensitive (MSSA) isolates (19.12%). PCR detects strains possessing toxin genes independent of their expression. The possession of genes for super-antigens seems to be a frequent and habitual trait of S. aureus more so in MRSA.