Introduction and objective:
Pseudomonas aeruginosa is an opportunistic pathogen that causes difficult with treating infections, especially in the immunocompromised and patients with some underlying disease. The aim of the study is to assess the antibiotic resistance, biofilm formation, and the presence of genes encoding various virulence factors in clinical isolates of P. aeruginosa.

Material and methods:
Seventy-three clinical isolates of Pseudomonas aeruginosa were tested. Antimicrobial Susceptibility Testing (AST) and carbapenemases production was performed in accordance with the EUCAST guidelines. The ability to form biofilm was assessed by crystal violet assay. Genes encoding selected virulence factors were detected using standard polymerase chain reaction (PCR).

Results:
Among the 73 clinical isolates of P. aeruginosa, 41.1% were resistant to imipenem, 61.6% to meropenem, 30.1% to ciprofloxacin and 15.1% to tobramycin. Over 20% of isolates were producers of MBL. Antibiotic resistance profiling revealed that 23.3% of strains were sensitive to all antibiotics, 60.3% were LDR phenotype, and 16.4% were MDR phenotype. The majority of strains (73.6%) were strong-biofilm producers, 17.0% were moderate and 9.4% were weak biofilm producers. PCR analysis showed the presence of lasB, aprE and prpL genes in most of the tested strains (93.1%, 87.7% and 74.0%, respectively). Among strong biofilm producers, 22.2% were MDR, 63.0% of strains represented LDR phenotype, and 14.8% were sensitive to all antibiotics. Moderate and weak biofilm producers were LDR and sensitive phenotypes only (respectively, 58.3% and 42.9 – LDR, 41.7 and 51.7% – sensitive).

Conclusions:
High frequency of MDR strains and their ability of biofilm formation and virulence factors may be a threat to effective therapy, and can increase morbidity and mortality of infected patients.