Evaluation of Phenotypic Methods for Detection of Klebsiella Pneumoniae Carbapenemase-Producing K. Pneumoniae in Tehran

Background: One of the main mechanisms of resistance to carbapenems is potential of Klebsiella pneumoniae to produce K. pneumoniae Carbapenemase (KPC). KPC is an important type of carbapenemase, which can hydrolyze carbapenems and other beta-lactam antibiotics. Modified Hodge Test (MHT) and use of boronic acid as a KPC inhibitor are two types of phenotypic methods, which are used for detection of carbanemase-producing bacteria. Specificity of these two phenotypic tests for identification of KPC was assessed in this study. Methods: Forty-four K. pneumoniae strains were isolated from wound infections of burn patients. All isolates were identified with specific biochemical tests. Carbapenem-resistant K. pneumoniae isolates were identified by disc diffusion method and analyzed with cut off-points of CLSI 2011 guideline. For detection of KPC-producing strains, carbapenem-resistant isolates were examined with two different phenotypic (i.e. MHT and Boronic acid) methods. Subsequently, strains with positive phenotypic methods were examined by PCR as a molecular method. Results: Twenty-eight (64%) out of 44 isolates were resistant to carbapenem according to CLSI breakpoints and 16 (36%) were susceptible. MHT was positive in all of carbapenem-resistant isolates but none of them have had the synergism effect between meropenem and boronic acid. Also, all isolates were negative for presence of KPC genes on gel electrophoresis. According to results MHT has not enough specificity for detection of KPC