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 expres...sed 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.
