Year : 2012 | Volume
: 136 | Issue : 2 | Page : 237--241
AmpC β-lactamases in nosocomial isolates of Klebsiella pneumoniae from India
Varsha Gupta1, Karthikeyan Kumarasamy2, Neelam Gulati1, Ritu Garg1, Padma Krishnan2, Jagdish Chander1
1 Department of Microbiology, Government Medical College & Hospital, Chandigarh, India
2 Department of Microbiology, Dr ALM PG IBMS, University of Madras, Chennai, India
Background & objectives: AmpC β-lactamases are clinically significant since these confer resistance to cephalosporins in the oxyimino group, 7-α methoxycephalosporins and are not affected by available β-lactamase inhibitors. In this study we looked for both extended spectrum β-lactamases (ESBL) and AmpC β-lactamases in Klebsiella pneumoniae clinical isolates.
Methods: One hundred consecutive, non-duplicate clinical isolates of K. pneumoniae collected over a period of one year (June 2008 - June 2009) were included in the study. An antibiotic susceptibility method was used with 10 antibiotics for Gram-negative infections which helped in screening for ESBL and AmpC β-lactamases and also in confirmation of ESBL production. The detection of AmpC β-lactamases was done based on screening and confirmatory tests. For screening, disc diffusion zones of cefoxitin <18 mm was taken as cefoxitin resistant. All cefoxitin resistant isolates were tested further by AmpC disk test and modified three dimensional test. Multiplex-PCR was performed for screening the presence of plasmid-mediated AmpC genes.
Results: Of the 100 isolates of K. pneumoniae studied, 48 were resistant to cefoxitin on screening. AmpC disk test was positive in 32 (32%) isolates. This was also confirmed with modified three dimensional test. Indentation indicating strong AmpC producer was observed in 25 isolates whereas little distortion (weak AmpC) was observed in 7 isolates. ESBL detection was confirmed by a modification of double disk synergy test in 56 isolates. Cefepime was the best cephalosporin in synergy with tazobactam for detecting ESBL production in isolates co-producing AmpC β-lactamases. The subsets of isolates phenotypically AmpC β-lactamase positive were subjected to amplification of six different families of AmpC gene using multiplex PCR. The sequence analysis revealed 12 CMY-2 and eight DHA-1 types.
Interpretation & conclusions: Tazobactam was the best β-lactamase inhibitor for detecting ESBL in presence of AmpC β-lactamase as this is a very poor inducer of AmpC gene. Amongst cephalosporins, cefepime was the best cephalosporin in detecting ESBL in presence of AmpC β-lactamase as it is least hydrolyzed by AmpC enzymes. Cefepime-tazobactam combination disk test would be a simple and best method in detection of ESBLs in Enterobacteriaceae co-producing AmpC β-lactamase in the routine diagnostic microbiology laboratories.
Professor, Department of Microbiology, Government Medical College & Hospital, Sector-32, Chandigarh 160 030
|How to cite this article:|
Gupta V, Kumarasamy K, Gulati N, Garg R, Krishnan P, Chander J. AmpC β-lactamases in nosocomial isolates of Klebsiella pneumoniae from India.Indian J Med Res 2012;136:237-241
|How to cite this URL:|
Gupta V, Kumarasamy K, Gulati N, Garg R, Krishnan P, Chander J. AmpC β-lactamases in nosocomial isolates of Klebsiella pneumoniae from India. Indian J Med Res [serial online] 2012 [cited 2021 Jun 24 ];136:237-241
Available from: https://www.ijmr.org.in/article.asp?issn=0971-5916;year=2012;volume=136;issue=2;spage=237;epage=241;aulast=Gupta;type=0