Investigation of the presence of carbapenemase in K. pneumoniae and E.coli strains isolated from blood culture by phenotypic and molecular methods

Carbapenem group antibiotics admitted as a significant treatment option in multi-drug resistant Enterobacteriaceae infections. Unfortunately, resistance to carbapenems has started to be seen frequently with showing up enzymes which hydrolyze this group of drugs. It is reported that carbapenemase enzymes such as KPC, OXA-48, NDM, VIM and IMP are responsible for this resistance mostly in the worldwide. Heteroresistance concept is another important issue about carbapenem resistance. Although, the mechanism of heteroresistance is not fully understood, it is thought to be effective on treatment success. In this study, carbapenem resistance of K.pneumoniae ve E.coli strains isolated from blood culture were investigated by different methods. The presence of carbapenemases were also determined by using phenotypic and molecular methods. In addition, the presence of carbapenem heteroresistance was investigated. A total of 301 Enterobacteriaceae strains, including 105 E.coli and 196 K.pneumoniae blood isolates, which sent to the Bacteriology Laboratory of Hacettepe University Hospital between January 2016 and August 2018, were included in the study. Carbapenem resistance was evaluated by using gradient test, disk diffusion test, sensititre microdilution test and Phoenix automated systems. The presence of carbapenemase was investigated by using CIM (Carbapenem Inactivation Method), MHT (Modifie d Hodge Test) and Rosco confirmation disc. Polymerase chain reaction (PCR) was used for the detection of the KPC, VIM, IMP, NDM-1 and OXA-48 gene regions. Resistance or decreased susceptibility to carbapenems was detected in 160 blood isolates by at least one method. The presence of at least one carbapenemase gene were detected in 147 (91.8%) of the isolates that were intermediate or resistant to carbapenem. OXA-48 (142/160; 88.7%) was the most common carbapenemase enzyme, following by NDM-1 (14/160;%8,7), VIM (5/160;%3,1) and KPC (1/160;%0,6). IMP enzyme was not observed in any of the isolates. The sensitivity and specificity of the MHT and CIM tests were found as 93.1%-94.1% and 69.3%-97.4%, respectively. When the carbapenemase confirmation disc results were compared with PCR results, the compliance was detected as 93,2 %. In this study carbapenem heteroresistance was detected in 21 (16 K.pneumoniae and 5 E.coli) isolates (6,9%). In 18 (85,7%) of these isolates OXA-48 enzyme was obtained. Our study is the second study showing carbapenem heteroresistance in OXA-48 positive K.pneumoniae isolates. However, this is first study about carbapenem heteroresistance detected in OXA-48 positive E.coli isolates.