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BioMed Research International
Volume 2014, Article ID 139305, 6 pages
http://dx.doi.org/10.1155/2014/139305
Research Article

Performance of Quantification of Modified Hodge Test: An Evaluation with Klebsiella pneumoniae Carbapenemase-Producing Enterobacteriaceae Isolates

1Faculdade de Farmácia, Universidade Federal do Rio Grande do Sul (UFRGS), 2752 Ipiranga Avenue, 90160-093 Porto Alegre, RS, Brazil
2Laboratório de Pesquisa em Resistência Bacteriana (LABRESIS), Centro de Pesquisa Experimental, Hospital de Clínicas de Porto Alegre (HCPA), 2350 Ramiro Barcelos Street, 90035-903 Porto Alegre, RS, Brazil
3Infectious Diseases Service, HCPA, 2350 Ramiro Barcelos Street, 90035-903 Porto Alegre, RS, Brazil

Received 1 December 2013; Accepted 18 February 2014; Published 26 March 2014

Academic Editor: Sanda Sardelić

Copyright © 2014 Vanessa Bley Ribeiro et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

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 β-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.