Detekcija mehanizama rezistencije na karbapeneme kod enterobakterija i vrste Pseudomonas aeruginosa

The aims of the research: to examine the presence of genes which encode carbapenemases among enterobacteria and Pseudomonas aeruginosa isolates with reduced sensitivity to carbapenems by using the polymerase chain reaction (PCR); to determine the most common mechanisms of resistance to carbapenems using phenotypic methods. To evaluate the phenotypic methods in relation to PCR as a reference method, and determine the most common phenotypes. Methods: 107 isolates from the Enterobacteriaceae family and 75 isolates of the species Pseudomonas aeruginosa were examined. Antimicrobial susceptibility was determined by the Kirby-Bauer disc-diffusion method and the automated Vitek2 system according to the recommendations of the Institute for Clinical and Laboratory Standards (CLSI). Using PCR and phenotypic methods, 56 enterobacterial isolates and 14 isolates of P. aeruginosa were tested. The results of the phenotypic tests were validated by a comparison with genotypic data and expressed through sensitivity, specificity, and positive and negative predictive value (PPV and NPV). Results: Carbapenemase genes were detected by the PCR method in 52 Enterobacteriaceae isolates: 24 blaNDM, 16 blaOXA-48, 10 blaNDM/ blaOXA-48, one isolate blaNDM/ blaOXA-48/ blaKPC , one isolate blaKPC/ blaNDM and six blaNDM genes in Pseudomonas aeruginosa. All of the tested isolates were negative for the blaVIM genes. Among the applied phenotypic tests, high specificity (in excess of 95%) was found for the modified Hodge test, the CARBA NP test, combined disc test and synergistic test, while high sensitivity (greater than 95%) was determined for thechromID CARBA agar. The most common phenotypes of resistance in enterobacteria were isolates resistant to all the tested antibiotics except for colistin and tigecycline, and in the case of Pseudomonas aeruginosa to colistin and piperacillin-tazobactam. Conclusions: Based on the results of sensitivity, specificity, PPV and NPV, the phenotypic methods for the detection of carbapenemase production represent reliable tests for the detection of this resistance mechanism both in enterobacteria and in Pseudomonas aeruginosa