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  Table of Contents  
Year : 2014  |  Volume : 32  |  Issue : 2  |  Page : 210-211

Characterisation of heteroresistant subcolonies for MBL, AmpC genes in Klebsiella pneumoniae and Acinetobacter baumannii

1 Department of Microbiology, Bharathiar University, Coimbatore, India
2 Department of Microbiology, Periyar University, Salem, Tamil Nadu, India

Date of Submission12-Mar-2013
Date of Acceptance17-Nov-2013
Date of Web Publication2-Apr-2014

Correspondence Address:
R Balagurunathan
Department of Microbiology, Periyar University, Salem, Tamil Nadu
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0255-0857.129869

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How to cite this article:
Shanthi J, Balagurunathan R. Characterisation of heteroresistant subcolonies for MBL, AmpC genes in Klebsiella pneumoniae and Acinetobacter baumannii. Indian J Med Microbiol 2014;32:210-1

How to cite this URL:
Shanthi J, Balagurunathan R. Characterisation of heteroresistant subcolonies for MBL, AmpC genes in Klebsiella pneumoniae and Acinetobacter baumannii. Indian J Med Microbiol [serial online] 2014 [cited 2020 Aug 8];32:210-1. Available from:

Dear Editor,

Acinetobacter baumannii and Klebsiella pneumoniae are associated with high rates of morbidity and mortality particularly among patients with prolonged hospitalisation, critically ill and exposure to invasive devices with various defense mechanisms. Heterogeneous phenotypes for carbapenem in these Gram-negative isolates have been reported where in small proportions of cells express a very high resistance to antimicrobials affecting the susceptibility test results. [1] The heteroresistant multivarient subpopulations are reported in both A. baumannii and K. pneumoniae isolates for cephalosporins, penicillins and carbapenem. [2] The present study aims to investigate the expression of metallo-β-lactamases and ampC genes in heterogeneous resistant colonies of A. baumannii and K. pneumoniae. We studied carbapenem resistance in non-repetitive consecutive 60 isolates of K. pneumoniae and A. baumannii for the presence of extended-spectrum β-lactamase and metallo β-lactamase production they were also screened for the presence of AmpC enzyme, efflux mechanism and MIC. Population analysis for heterogeneous phenotype was determination for 16 strains of K. pneumoniae and A. baumannii isolated from pus, blood, sputum and ET secretions of ICU patients displaying heterogeneous phenotype with high ceftazidime and meropenem resistance and a susceptible control strain. [3]

Multiplex PCR analysis of 16 phenotypically positive heteroresistant K. pneumoniae and A. baumannii was executed for pAmpC and MBLs genes with the primers designed for conserved regions of blaIMP, blaVIM , ampC FOX, DHA, MOX and ACT. [4] Population analysis assay showed heteroresistant subcolonies grew within the zone till 32 μg/ml antibiotics at a frequency of ~1.6 × 10 -5 in both the strains; antibiotic-free media the colonies were at ~3 × 10 -5 frequency. Among the 16 heteroresistant colonies seven strains expressed either ampC or MBL gene. FOX and MOX ampC genes were present in two of K. pneumoniae strains and two others expressed ACT group of genes (25%). Two A. baumannii strains had an inducible plasmid-mediated AmpC β-lactamases DHA-1. MBL gene blaIMP and blaVIM was absent in A. baumannii and only blaIMP MBL genes was present in K. pneumoniae [Figure 1]. Group B metallo-β-lactamase is not involved in carbapenem resistance among A. baumannii isolates and K. pneumoniae was positive for blaIMP and ampC genes. [5] This study shows that heteroresistant colonies carry MBL and AmpC β-lactamases; this subpopulation of resistant bacteria often will be selected by certain drug concentration leading to regrowth. Hence, treatment with cephalosporins or carbapenems may alone lead to therapeutic failures especially if these colonies are present.
Figure 1: Analysis of PCR-amplifi ed products for ampC and MBLs gene on 1% agarose gel. Lanes are labelled with respective template DNA, M-100-bp ladder. Top gel picture of K. pneumoniae amplicons for both ampC and MBLs genes obtained, in bottom gel only DHA type ampC product from A. baumannii was amplifi ed. Gel-1, lane-1and4 blaIMP 188 bp, Lane-2 ACT group 300 bp, MOX group 500 bp, FOX group 200 bp gel-2, DHA group 405bp A. baumannii

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 ~ References Top

1.Pournaras S, Kristo I, Vrioni G, Ikonomidis A, Poulou A, Petropoulou D, et al. Characteristics of meropenem heteroresistance in Klebsiella pneumoniae carbapenemase-producing clinical isolates of K. pneumoniae. J Clin Microbiol 2010;48:2601-4.  Back to cited text no. 1
2.Hung KH, Wang MC, Huang AH, Yan JJ, Wu JJ. Heteroresistance to cephalosporins and penicillins in A. baumannii. J Clin Microbiol 2012;50:721-6.  Back to cited text no. 2
3.Tato M, Morosini L, García S, Albertí S, Coque MT, Cantón R. Carbapenem Heteroresistance in VIM-1-Producing Klebsiella pneumoniae isolates belonging to the same clone: Consequences for Routine Susceptibility Testing. J Clin Microbiol 2010;48:4089-93.  Back to cited text no. 3
4.Perez-Perez FJ, Hanson ND. Detection of plasmid-mediated AmpC beta-lactamase genes in clinical isolates by using multiplex PCR. J Clin Microbiol 2002;40:2153-62.  Back to cited text no. 4
5.Yong D, Toleman MA, Giske CG, Cho HS, Sundam K, Lee K, et al. Characterisation of a new metallo-beta-lactamases gene, bla and a novel erythromycin esterase gene carried on a unique genetic structure in K. pneumoniae sequence type 14 from India. Antimicrob Agents Chemother 2009;53:5046-54.  Back to cited text no. 5


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