title: Occurrence and detection of AmpC beta-lactamases among Gram-negative clinical isolates using a modified three-dimensional test at Guru Tegh Bahadur Hospital, Delhi, India.
abstract: AmpC enzymes can be differentiated from other extended-spectrum beta-lactamases by their ability to hydrolyse cephamycins as well as other extended-spectrum cephalosporins. The present study was designed to determine the occurrence of AmpC enzyme-harbouring Gram-negative clinical isolates in a tertiary care hospital in Delhi, India. Among the 135 clinical isolates of Gram-negative bacilli tested, 20.7% were found to harbour AmpC enzymes using a modified three-dimensional test. Inhibition of zone distortion in the presence of cloxacillin confirmed AmpC-harbouring isolates. Maximal incidence of AmpC producers was found among Acinetobacter spp. (42.8%) followed by Klebsiella pneumoniae isolates (33.3%). No AmpC-harbouring isolates revealed decreased susceptibility to cefoxitin. Therefore, Gram-negative bacilli showing resistance to any cephalosporin or aztreonam irrespective of cefoxitin susceptibility should be screened for the AmpC enzyme. The modified three-dimensional test is easy to carry out and can be applied as a phenotypic screening method for detection of AmpC-harbouring Gram-negative organisms. This is the first study to determine the occurrence of AmpC beta-lactamases from India.
authors.affiliation: Department of Microbiology, University College of Medical Sciences and Guru Tegh Bahadur Hospital, Dilshad Garden, 110095 Delhi, India. manchandavikas@hotmail.com
authors.forename: Vikas
authors.initials: V
authors.lastname: Manchanda
authors.forename: Narendra P
authors.initials: NP
authors.lastname: Singh
mesh_terms: D001426:Bacterial Proteins; D001431:Bacteriological Techniques / Q000379:methods*; D002440:Cefoxitin / Q000494:pharmacology; D002513:Cephamycins / Q000494:pharmacology; D024881:Drug Resistance, Bacterial; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics; D006090:Gram-Negative Bacteria / Q000201:enzymology*; D016905:Gram-Negative Bacterial Infections / Q000382:microbiology*; D006801:Humans; D007194:India; D008826:Microbial Sensitivity Tests; D010641:Phenotype; D001618:beta-Lactamases / Q000032:analysis*
chemical_list: D001426:Bacterial Proteins; D002513:Cephamycins; D002440:Cefoxitin; C048795:AmpC beta-lactamases; D001618:beta-Lactamases