Effectiveness of Modified Hodge Test to detect NDM-1 Carbapenemases: an experience from Pakistan

Objective: To assess the effectiveness of Modified Hodge Test and its clinical utility as a phenotypic method in detecting carbapenemase. Methods: The prospective study screened all enterobacteriaceae isolated from blood, tracheal aspirate, urine and pus aspirates at the Microbiology Laboratory of Aga Khan University Hospital, Karachi, from June 2009 to July 2010. The isolates were screened according to susceptibility zone size ≤ 23mm of meropenem on Kirby-Bauer disc diffusion followed by confirmation with minimum inhibitory concentrations ?0.5 μg/ml for meropenem by E-test method. The screened isolates were subjected to phenotypic assay (Modified Hodge Test) with subsequent confirmation with the genotypic assay. SPSS 19 was used for statistical analysis. Results: A total of 7192 enterobacteriaceae were screened. Of these, 100 (1.39%) isolates were prospectively included in the study: Klebsiella pneumoniae 63 (63%); Escherichia coli 32 (32%); others 5 (5%). Out of the 100 isolates, 93 (93%) showed positive polymerase chain reaction results for New Delhi-Metallo-beta-lactamase (NDM-1) gene, and 69 (69%) isolates showed positive Modified Hodge Test. Four (5.8%) polymerase chain reaction negative isolates were found positive by Modified Hodge Test (false positive), which showed sensitivity of 42.8%, and specificity of 69.8% with a positive predictive value of 94.2% and a negative predictive value of 9.6%. Conclusion: The Modified Hodge Test is a simple cost-effective method for phenotypic of carbapenemases detection in carbapenem-resistant enterobacteriaceae. This phenotypic test can be routinely performed in the clinical laboratories to detect NDM-1 carbapenemases production in the absence of molecular assays in resource-constrained settings.