title: Phenotypic & molecular characterization of AmpC β-lactamases among Escherichia coli, Klebsiella spp. & Enterobacter spp. from five Indian Medical Centers.
abstract: OBJECTIVE
  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.
  
  
  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.
authors.affiliation: Prof Benjamin M Pulimood Laboratories for Infection, Immunity & Inflammation, Medicine Unit I & Infectious Diseases, Christian Medical College, Vellore, India.
authors.forename: Anand
authors.initials: A
authors.lastname: Manoharan
authors.forename: Madhan
authors.initials: M
authors.lastname: Sugumar
authors.forename: Anil
authors.initials: A
authors.lastname: Kumar
authors.forename: Hepzibah
authors.initials: H
authors.lastname: Jose
authors.forename: Dilip
authors.initials: D
authors.lastname: Mathai
authors.forename: G C
authors.initials: GC
authors.lastname: Khilnani
authors.forename: Arti
authors.initials: A
authors.lastname: Kapil
authors.forename: Geetha
authors.initials: G
authors.lastname: Francis
authors.forename: Kavitha
authors.initials: K
authors.lastname: Radhakrishnan
authors.forename: T K
authors.initials: TK
authors.lastname: Dutta
authors.forename: S C
authors.initials: SC
authors.lastname: Parija
authors.forename: R
authors.initials: R
authors.lastname: Narang
authors.forename: D K
authors.initials: DK
authors.lastname: Mendiratta
authors.forename: Vijayshree
authors.initials: V
authors.lastname: Deotale
authors.forename: A K
authors.initials: AK
authors.lastname: Baronia
authors.forename: K N
authors.initials: KN
authors.lastname: Prasad
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000378:metabolism*; D003428:Cross Infection / Q000382:microbiology*; D024901:Drug Resistance, Multiple, Bacterial; D004754:Enterobacter / Q000187:drug effects / Q000201:enzymology* / Q000302:isolation & purification; D004926:Escherichia coli / Q000187:drug effects / Q000201:enzymology* / Q000302:isolation & purification; D005838:Genotype; D016905:Gram-Negative Bacterial Infections / Q000382:microbiology*; D006801:Humans; D007709:Klebsiella / Q000187:drug effects / Q000201:enzymology* / Q000302:isolation & purification; D008826:Microbial Sensitivity Tests; D018440:beta-Lactam Resistance; D001618:beta-Lactamases / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; C048795:AmpC beta-lactamases; D001618:beta-Lactamases