Objective: Carbapenem resistance has become an important public health problem due to its high mortality and limited treatment options. Therefore, there is a need for reliable and simple tests that detect the carbapenem resistance mechanism in a short time. The aim of this study was to determine the presence of carbapenemase, ESBL, and AmpC in carbapenem-resistant Klebsiella spp. and Escherichia coli isolates using disc diffusion, combined disc and disc antagonism test methods on the same plate.

Methods: Carbapenem-resistant Klebsiella spp. and E.coli isolates routinely isolated from patient culture samples in a university hospital between December 2017 and December 2018, were included in the study. Combined disk method was used as confirmatory test for ESBL, KPC type and metallo-beta-lactamase, and temocillin disk diffusion test was used for OXA-48 type carbapenemase in line with the recommendations of the European Committee for Antimicrobial Susceptibility Testing. The disc diffusion test was used for plasmidmediated AmpC beta-lactamase identification and the disc antagonism test for inducible (chromosomal) AmpC beta-lactamase. BAA-1705 K. pneumoniae producing KPC-2 type carbapenemase was used as the control strain.

Results: Carbapenem resistance was detected in a total of 75 isolates, of which 74.6% (n=56) were Klebsiella pneumoniae, 22.6% (n=17) Escherichia coli, 1.3% (n=1) Klebsiella ozanea and 1.3% (n=1) were Klebsiella aerogenes. Metallo-beta-lactamase type carbapenemase-associated resistance was determined in 24(31,5%) isolates, ESBL in 17(22,3%), AmpC in 4 (5,2%) isolates, and OXA-48-related resistance in 31(40,7%) isolates.

Conclusion: Rapid detection of resistance mechanisms is important for appropriate antimicrobial therapy and infection control measures. The method we used in the study creates an easy and applicable algorithm.