Assessing the antibiotic resistance patterns dependent on efflux pump genes of Staphylococcus aureus strains isolated from Blood culture in Shahid Beheshti hospital centers during 1396-1397

Staphylococcus aureus is a major cause of nosocomial infections in the world. Efflux pumps are well known as a key role to fluoroquinolone resistance in methicillin-resistant Staphylococcus aureus (MRSA). The present study was performed to determine resistance to antimicrobial agents related to efflux pumps isolates recovered from blood cultures of patients referred to several hospitals affiliated with Shahid Beheshti University of Medical Sciences between 1396-1397.

In the present descriptive cross-sectional study, a total of 100 clinical samples were collected from blood cultures over a 12-month period. S. aureus isolates were identified using standard microbiological tests. Antimicrobial susceptibility patterns were determined using disk diffusion method and micro-dilution method. Subsequently, the presence of norA efflux pump gene was detected using PCR method. Finally, active efflux pumps were evaluated using ciprofloxacin and ethidium bromide MICs. Polymerase Chain Reaction (PCR) and sequencing were used to investigate the norA efflux pump gene. Chi-square test was used for statistical analyses.

Among 100 clinical samples, 38 out of 45 MRSA isolates (84.4%) showed resistance to ciprofloxacin. Moreover, the norA gene was found in 100% of ciprofloxacin resistant isolates. Among 38 ciprofloxacin-resistant isolates, 8 isolates showed active efflux activity by reducing EtBr and ciprofloxacin MIC values by 2 to 4 folds in the presence of CCCP (carbonyl cyanide 3-chlorophenylhydrazone).

It seems that a rising trend of antimicrobial resistance among S.aureus isolates to different antibiotics has  become a widespread concern in infection control.