Performance of quantification of Modified Hodge Test: an evaluation with Klebsiella pneumoniae carbapenemase-producing Enterobacteriaceae isolates.

Modified Hodge Test (MHT) has been suggested as screening tests for carbapenemases, but concerns regarding its difficult interpretation and common false-positive results obtained in the presence of other ß -lactamases have been noted. This study aimed to quantify the enhanced growth formed by the indicator strain and thus evaluate the performance of a quantitative interpretation of MHT for KPC screening. MHT was performed in 50 KPC-producing isolates and 334 non-carbapenemase-producing isolates, using ertapenem (ETP) and meropenem (MEM) as substrates. The size of enhanced growth of indicator strain was measured for each isolate tested and for the positive control used, and a ratio was calculated. Our results revealed 17 different ETP and MEM ratios, with distinct sensitivity (SN) and specificity (SP). Higher SN combined to higher SP was achieved when ETP and MEM ratios were 0.45, with a SN value of 96% for both substrates and SP values of 99.4% and 100% for ETP and MEM, respectively. The quantification with both substrates increased SP of the test for KPC detection. Considering that MHT is the unique phenotypic test that is referred to by CLSI, a more accurate approach for its interpretation could be applied to make it a more useful tool.

Molecular characterization of Klebsiella pneumoniae carbapenemase-producing isolates in southern Brazil.

Carbapenem-resistant Enterobacteriaceae have been frequently reported worldwide. They represent a serious concern because of the limited therapeutic options. The aim of this study was to investigate the molecular epidemiology of 14 Klebsiella pneumoniae carbapenemase (KPC) producers among 345 clinical isolates of Enterobacteriaceae with reduced susceptibility to carbapenems recovered from 11 separate hospitals in southern Brazil. The blaKPC-2 gene was detected in 14 isolates (4 %): six Enterobacter cloacae, five K. pneumoniae and three Serratia marcescens. Most of these isolates exhibited high-level resistance against ß-lactams and ciprofloxacin, while the most active drugs were polymyxin B and amikacin. Genetic environment analysis, based on the classical Tn4401 structure, revealed six distinct platforms. Plasmids carrying blaKPC-2 were not typable and most were approximately 20 kb. Only KPC carbapenemases were found among the isolates studied, highlighting the local relevance of these enzymes in acquired resistance to carbapenems in Enterobacteriaceae. Our results contribute to the understanding of carbapenem resistance in Enterobacteriaceae and to the molecular characterization of KPC-2-producing isolates in Brazil.