Evaluation of the Performance of Routine Phenotypic Methods for Accurate and Rapid Detection of Carbapenem-Resistant Enterobacteriaceae in Clinical Samples

Abstract

Resistance to carbapenems among Enterobacteriaceae has emerged as a global threat, because carbapenems are considered the most potent antimicrobials used for treatment of severe Gramnegative infections. This study aimed to compare between the phenotypic and genotypic methods used for detection of carbapenemase-producing clinical isolates of carbapenem resistant Enterobacteriaceae (CRE). We evaluated modified Hodge Test (MHT), EDTA-imipenem combined disc test and modified carbapenem inactivation method (mCIM) in comparison with the multiplex polymerase chain reaction (PCR) method (gold standard) for detection of carbapenemase activity of 65 CRE isolates from patients admitted to a tertiary care hospital. The commonest source of CRE was blood culture (35%). The most common CRE type was Klebsiella pneumoniae (90.7%). The bacterial isolates resistant to meropenem, imepenem, amikacin and gentamicin were 98.64%, 97.94%, 94% and 93%, respectively. Resistance of CRE to all classes of cephalosporin groups, quinolone and combination drugs was 100%. On the other hand, CRE preserved 100% sensitivity to polymyxin-B and colistin. Out of 65 CRE isolates, we detected blaOXA-48 alone in 54%, blaNDM alone in 22 %, blaKPC alone in 9.2 % and coexistence of more than one gene in 14.5% of isolates, as 10% (7/65) of the isolates showed (blaOXA-48 + blaNDM). While, 3% (2/65) have (blaOXA-48 +blaKPC) and others 1.5% (1/65) have (blaNDM + blaKPC). We didn't detect neither IMP nor VIM genes. Multiplex PCR was superior to phenotypic methods in detection and identification of carbapenemase genes. Among phenotypic methods, mCIM was the most sensitive for detection of carbapenemase production.