Frequency of mecA and blaZ genes in isolates of Staphylococcus aureus isolated from clinical samples by PCR method

Staphylococcus aureus (S. aureus) is the most common cause of nosocomial infections. Treatment of Staphylococcal infections has become more complicated due to the emergence of methicillin-resistant S.aureus (MRSA) strains. This study was done to determine the frequency of methicillin resistance encoding gene (mecA) and β-lactamase resistance encoding gene (blaZ) in S. aureus isolates from clinical samples using Polymerase Chain Reaction (PCR) method.

This descriptive-analytic study was carried out on 59 S. aureus isolates from clinical samples in Gorgan hospitals from January-February 2017 to June-July 2017. All the isolates were identified using gram staining, catalase test, tube coagulase test, growth on Mannitol salt agar medium and the DNase test in the Microbiology Laboratory .Antibiotic resistance was evaluated using the standard disk diffusion.  Iodometric method was used to detect β-lactamase production / activity in this bacterium. PCR test was done to detect mecA and blaZ genes.

All S. aureus isolates (100%) clinical samples possessed blaZ gene, followed by 27 isolates (45.8%) possessed mecA gene (MRSA), which these isolates possessed mecA gene were concurrently positive for blaZ gene. 5% of oxacillin-resistant strains and 3% of cefoxitin-resistant strains possessed mecA gene and 47 isolates (79.4%) carrying blaZ gene were β-lactamase-positive in phenotypic method.

This study showed that in all clinical samples isolated S. aureus isolates which these isolates possessed mecA gene were concurrently positive for blaZ gene.