Molecular Epidemiology of Beta-Lactamases in Ceftazidime-Resistant Pseudomonas aeruginosa Isolates

Abstract

Pseudomonas aeruginosa is an important opportunistic pathogen that cause mainly nosocomial infections especially in the immunocompromised patients, the elderly and patients with severe burns. The bacterial feature of developing high degree of resistance against several antibiotics leads to increased morbidity and mortality of P.aeruginosa infections. The aims of this study were to investigate the antibiotic susceptibilities of P.aeruginosa strains isolated from hospitalized patients and to determine the presence of resistance enzymes namely PER, GES, KPC, VIM, IMP and OXA. A total of 195 P.aeruginosa strains isolated from different clinical samples (29 sputum, 67 wound, 53 tracheal aspirate, 23 blood, 18 urine, 3 cerebrospinal fluid, 2 pleural fluid) of inpatients (134 male, 61 female) in Afyon Kocatepe University School of Medicine Hospital between 2010-2012, were included in the study. The isolates were identified by conventional methods and automated systems (VITEK 2, BioMerieux, France), and their antibiotic susceptibilities were detected by disk diffusion and E-test methods. Inducible beta-lactamase (IBL), extended-spectrum beta-lactamase (ESBL) and metallo-beta-lactamase (MBL) productions of the isolates were phenotypically investigated by double disk induction, double disk synergy and E-test methods, respectively. The presence of resistance genes encoding PER, GES, KPC, VIM, IMP and OXA enzymes were determined by real-time polymerase chain reaction, and sequence analysis was applied to positive samples. In our study, the antibiotic resistance rates of 195 P.aeruginosa strains were found as follows: ceftazidime 100%, tazobactam/piperacillin 90.8%, aztreonam 60.5%, cefepime 50.2%, imipenem 48.2%, meropenem 47.2%, ofloxacin 47.2%, piperacillin 44.1%, levofloxacin 31.3%, ciprofloxacin 26.2%, gentamicin 11.8%, amikacin 8.7% and tobramycin 6.2%. With the use of phenotypical methods, IBL, ESBL and MBL production rates in the isolates were detected as 89.2% (174/195), 30.7% (60/195) and 26.7% (52/195), respectively. Molecular studies showed that, five strains harboured OXA-10, four OXA-14, four VIM-2, two IMP-1, 26 GES-1 and 87 ABC transporter permease genes, while PER and KPC genes were not detected in any of the isolates. In conclusion, it was considered that the detection of beta-lactamase genes in bacteria and the identification of beta-lactamase types may provide facilities in selection of antibiotics, monitorization of therapy, prevention of resistance development of infection control programs.