What should be the criteria for application of modified Hodge test for carbapenemases in Klebsiella pneumoniae?

Abstract

Carbapenems are the beta lactam antibiotics with the broadest spectrum of antibacterial activity and are used for management of a wide variety of infections by Extended spectrum beta lactamasesESBLs and Ambler Class (AmpC) enzymes producing enterobacteriaceae, Acinetobacter spp. and Pseudomonas spp. involved in lower respiratory tract, intra-abdominal and urinary tract infections and infections of skin, soft-tissue, bones and joints. Carbapenems are especially useful for cephalosporin resistant nosocomial bacteria such as Citrobacter freundii and Enterobacter. Production of carbapenem hydrolyzing enzymes, carbapenemases and resistance to 3 rd generation cephalosporins with porin loss are the major mechanisms involved in carbapenem resistance. In Klebsiella pneumoniae carbapenemases (KPC) belong to AmpC A, KPC, class B metallo beta lactamases (MBL) and class D oxacillinases. Though AmpC A KPC type enzymes are the major carbapenemases involved in carbapenem resistance in Klebsiella pneumoniae, emergence of AmpC B MBL [1] and oxacillinases [2] has been reported recently. Thus, the detection of carbapenem resistance has become important to prevent treatment failure and limiting the spread of enzyme producing strains.We studied carbapenem resistance in 50 consecutive, non-repeat, invasive isolates of K. pneumoniae by disc diffusion (DD) test, microbroth (MIC) dilution, modified Hodge test (MHT) for carbapenemases as per Clinical and Laboratory Standards Institute (CLSI) guidelines. [3] The strains were subjected to imipenem-ethylenediaminetetraacetic acid disc synergy test for MBL detection and were screened for the presence of ESBLs by the double disc potentiation method and for the presence of AmpC by Cefoxitin disc approximation test. [4] Susceptibility to the antimicrobials such as fluoroquinolones and aminoglycosides was also tested. Of the 50 strains tested, carbapenem resistance was indicated in 21 strains by at least one of the three methods used. Fourteen strains exhibited carbapenem resistance or intermediate sensitivity by CLSI criteria with DD or MIC. Of the 18 MHT positive strains, 07 were carbapenem sensitive by DD or MIC criteria. MIC ranged from 0.5 µg/ml to ≥64 µg/ml in carbapenemase producers. Three strains with MIC ≥8 were MHT negative. Correlation between MHT and MIC values and DD results is shown in the Table 1. Of the total 50 strains studied, 41 were ESBL producers and 20 were AmpC producers of which 90% were also ESBL producers. In three carabapenem resistant strains, resistance mechanism could be probably attributed to AmpC/ESBL production with porin loss as MHT was negative. None of the strains tested was MBL producer. In as many as 12 carbapenemases producing strains MICs lower than the susceptible break point were observed. All 24 strains were amikacin sensitive.In as many as 07 carbapenemases producing strains MICs lower than the susceptible break point were observed indicating that the detection of carbapenemases if is limited to only those strains exhibiting MIC or DD criteria as per CLS...

Evaluation of Modified Hodge Test as a Non-molecular Assay for Accurate Detection of KPC-producing Klebsiella pneumoniae

“…As a phenotypic test, MHT is widely used for first-line detection of carbapenem resistance in clinical laboratories (Carvalhaes et al 2010;Cury et al 2012;Chande et al 2013). In the current study, we evaluated the efficiency of MHT test with two different carbapenem disks as substrate for identification of KPC enzyme and compared it using PCR.…”