|Year : 2013 | Volume
| Issue : 3 | Page : 318-319
What should be the criteria for application of modified Hodge test for carbapenemases in Klebsiella pneumoniae?
C Chande, P Veer, A Chivate, SG Joshi, A Chowdhary
Department of Microbiology, Grant Medical College and Sir J. J. Group of Hospitals, Mumbai, Maharashtra, India
|Date of Submission||23-Apr-2013|
|Date of Acceptance||30-Apr-2013|
|Date of Web Publication||25-Jul-2013|
Department of Microbiology, Grant Medical College and Sir J. J. Group of Hospitals, Mumbai, Maharashtra
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Chande C, Veer P, Chivate A, Joshi S G, Chowdhary A. What should be the criteria for application of modified Hodge test for carbapenemases in Klebsiella pneumoniae?. Indian J Med Microbiol 2013;31:318-9
|How to cite this URL:|
Chande C, Veer P, Chivate A, Joshi S G, Chowdhary A. What should be the criteria for application of modified Hodge test for carbapenemases in Klebsiella pneumoniae?. Indian J Med Microbiol [serial online] 2013 [cited 2019 Sep 19];31:318-9. Available from: http://www.ijmm.org/text.asp?2013/31/3/318/115673
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  and oxacillinases  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.  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.  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.
|Table 1: Comparison of disc diffusion, MIC determination and MHT for carbapenem resistance in Klebsiella pneumoniae|
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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 CLSI, 41% carbapenemases producers would go unnoticed. A proportion of carbapenemase isolates have low MICs for carbapenemes have been reported in the literature.  In view of the rampant use of carbapenemases in tertiary health care settings, carbapenemase screening is essential for all the strains of K. pneumoniae, irrespective of the results of DD or broth dilution tests. If MHT testing is kept limited to the isolates testing intermediate or resistant isolates only, many carbapenemase producing strains would go unnoticed. However, as the false MHT positive has also been observed in strains producing ESBL and with porin loss and the strains harbouring Cefotaximases Munich CTX-M type and AmpC  results of all the three tests should be taken into account before reporting on carbapenem resistance. The sensitivity of all the strains to amikacin in the present study indicates an availability of the option for the treatment of the infections caused by carbapenemases producing K. pneumoniae.
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