Antimicrobial resistance, biofilm-forming ability and virulence potential of Pseudomonas aeruginosa isolated from burn patients in northern Iran

Objectives: Pseudomonas aeruginosa is a frequent cause of infectious diseases, such as burn and wound infections, making it one of the most menacing opportunistic pathogens. The aim of this study was to investigate the antimicrobial resistance, biofilm-forming ability, and frequency of genes involved in biofilm formation and virulence of P. aeruginosa isolated from burn infections in Iran.

Methods: Resistance of 90 P. aeruginosa isolates to 12 antimicrobial agents as well as production of extended-spectrum β-lactamase (ESBL) and metallo-β-lactamase (MBL) enzymes were assessed phenotypically according to Clinical and Laboratory Standards Institute (CLSI) guidelines. Biofilm-forming capacity was assayed in a microtitre plate. The frequency of biofilm- and virulence-associated genes was investigated by PCR. Mutations in gyrA and parC in ciprofloxacin-resistant isolates were also determined by PCR.

Results: In phenotypic assays, 72.2% (65/90) of P. aeruginosa isolates were multidrug-resistant (MDR), 55.5% (50/90) and 35.6% (32/90) were positive for ESBL and MBL production, respectively, and 67.8% (61/90) were positive for biofilm formation. Biofilm- and virulence-associated genes were identified in >50% of the P. aeruginosa isolates, with toxA and lasB being the most frequent. All of the virulence genes were more common in biofilm-forming and MDR phenotypes. Two point mutations in gyrA and one in parC in high-level ciprofloxacin-resistant isolates were identified.

Conclusions: The results of this study indicate that there is a high frequency of multidrug resistance and a high percentage of virulence-associated genes present in clinical P. aeruginosa isolates in Iran.