Determination of antibiotic resistance, inducible beta-lactamase and metallo beta-lactamase rates for nosocomial pseudomonas aeruginosa isolates in Turgut Özal Medical Center within 2009 year

Objectives: Pseudomonas aeruginosa that cause nosocomial infections is naturally resistant to many antibiotics. Amongst hospitals, bacterial resistance to currently used antibiotics may alter. Beta-lactamase enzymes and various resistance mechanisms cause to antibiotic resistance.This study aims to investigate antibiotic resistance and inducible beta-lactamase and metallo beta-lactamase rates of P. aeruginosa strains that isolated from nosocomial infections. Another aim of this study was to compare the three different phenotypic methods for screening of MBL production.Materials and Methods: P. aeruginosa isolates were identified by conventional methods. According to the standards of Clinical and Laboratory Standards Institute (CLSI), antibiotics susceptibility tests were performed by Kirby-Bauer disk diffusion method. Imipenem and meropenem E test (AB Biodisk, Sweden) were used for verification of carbapenem resistance. Disk induction method was used for determination of IBL production. Modified Hodge test and imipenem/EDTA Combined disk test and MBL E test were used for detection of MBL production and the results of these tests were compared.Findings: Eighty-six percent of 110 P. aeruginosa strains have been isolated from urine, tracheal aspirates, blood and wound specimens. P. aeruginosa were most frequently isolated from patients in Anesthesia and Reanimation Intensive Care Unit, Internal Medicine Intensive Care Unit, Clinic of General Surgery and Neurology service. P. aeruginosa isolates were most susceptible to antibiotics respectively, colistin, ceftazidime, cefepime, amikacin, piperacillin and ciprofloxacin. One hundred percent of isolates were susceptible to colistin whereas, there was no statistical difference for activity between colistin and ceftazidime, cefepime antibiotics (p>0.10). Ceftazidime and cefepime were found significantly more active than carbapenems(p:<0,0001-0,002). Among aminoglycosides, amikacin has the highest susceptibility rate. Netilmicin, imipenem, aztreonam, and meropenem, respectively they have the most resistance rates for P. aeruginosa isolates. IBL disk induction method was positive in 90% of the isolates. Two isolates that gave positive results with both of the Combined disk test and the MBL E test were considered as MBL producing isolates. Among all of the isolates, MBL positivity rate was found as 1,8%.Results: The resistance rates to carbapenems(especially to imipenem) were higher than the other beta lactam antibiotics, because of, they are preferred antibiotics for the empiric therapy of P. aeruginosa infections in our hospital. Because of, the susceptibility rates to ceftazidime, cefepime or piperacillin/tazobaktam were very high, combined use of these antibiotics with other antipseudomonal drugs may be a much more effective approach for empiric treatment of P. aeruginosa infections, compared to stand-alone carbapenem usage. As a screening test for MBL enzymes IMP/EDTA Combined disk test and MBL E test in our study were consistent with each other 86%, and the modified Hodge test yielded inconsistent results. IMP/EDTA Combined disk test is safe, simple and fast as much as MBL E test; it also has a much lower cost compared to MBL E test. IMP/EDTA Combined disk test may be suitable for screening of MBL producting isolates in routine laboratory studies. Rapid detection of MBL positive isolates and effective implementation of infection control measures are possible owing to IMP/EDTA Combined disk test.Key words: Pseudomonas aeruginosa, antibiotic susceptibility, inducible beta-lactamase, metallo beta-lactamase.