Publication Type:

Journal Article


Indian Journal of Medical Research, Volume 135, Number 3, p.359-364 (2012)



amikacin, Anti-Bacterial Agents, antibiotic resistance, antibiotic sensitivity, article, Bacterial, Bacterial Proteins, bacterial strain, bacterium isolate, beta lactamase AmpC, beta-Lactam Resistance, beta-Lactamases, boronic acid derivative, cefoxitin, controlled study, Cross Infection, disk diffusion, Drug Resistance, Enterobacter, enzyme analysis, epsilometer test, ertapenem, Escherichia coli, extended spectrum beta lactamase, extended spectrum beta lactamase producing Enterobacteriaceae, genotype, Gram-Negative Bacterial Infections, Humans, imipenem, India, Klebsiella, levofloxacin, meropenem, Microbial Sensitivity Tests, minimum inhibitory concentration, multidrug resistance, Multiple, Multiplex Polymerase Chain Reaction, nonhuman, phenotype, piperacillin plus tazobactam, plasmid, prospective study, tigecycline


Background & objectives: AmpC β-lactamases which are often plasmid mediated hydrolyze all β-lactam antibiotics except cefepime and carbapenems. We evaluated the presence of AmpC β-lactamases among Enterobacteriaceae strains recovered prospectively from patients at five Indian tertiary care centres. Methods: The study included 909 consecutive Gram-negative isolates recovered from clinically significant specimens during June 2007 - May 2008 as part of an ICMR-ESBL study. Among the study isolates, 312 were found to be cefoxitin resistant by disc diffusion test (DDT). Minimum inhibitory concentration (MIC) determination by E test was done against amikacin, levofloxacin, impinem, meropenem, ertapenem, tigecycline and piperacillin-tazobactam. Combined DDT using phenyl boronic acid as inhibitor with cefoxitin was used for phenotypic confirmation of AmpC phenotype. The common Amp C genotypes ACC, FOX, MOX, DHA, CIT and EBC were detected by multiplex PCR. Results: Plasmid mediated Amp C phenotype was confirmed in 114 of the 312 (36.5%) cefoxitin resistant isolates with 255 (81.7%) showing multidrug resistance. Susceptibility to tigecycline was highest (99%) followed by imipenem, meropenem (97%), ertapenem (89%), amikacin (85%), and piperacillin-tazobactam (74.6%). Levofloxacin resistance was 82 per cent. ESBL co carriage was observed among 92 per cent of Amp C producers. Among 114 Amp C producers, 48 could be assigned a genotype, this included CIT- FOX (n=25), EBC (n=10), FOX (n = 4), CIT (n=3), EBC-ACC (n=2) and one each of DHA, EBC-DHA, FOX -DHA and FOX-EBC-DHA. Interpretation & conclusions: Overall, AmpC phenotypes were found in 12.5 per cent isolates, multidrug resistance and ESBL co-carriage among them was high suggesting plasmid mediated spread. The study results have implications in rational antimicrobial therapy and continued surveillance of mechanisms of resistance among nosocomial pathogens.


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Cite this Research Publication

Aa Manoharan, Sugumar, Ma, Kumar, Ab, Jose, Ha, and Mathai, Da, “Phenotypic & molecular characterization of AmpC β-lactamases among Escherichia coli, Klebsiella spp. & Enterobacter spp. from five Indian Medical Centers”, Indian Journal of Medical Research, vol. 135, pp. 359-364, 2012.