title: Detection and occurrence of plasmid-mediated AmpC in highly resistant gram-negative rods.
abstract: OBJECTIVE
  The aim of this study was to compare the current screening methods and to evaluate confirmation tests for phenotypic plasmidal AmpC (pAmpC) detection.
  
  
  METHODS
  For this evaluation we used 503 Enterobacteriaceae from 18 Dutch hospitals and 21 isolates previously confirmed to be pAmpC positive. All isolates were divided into three groups: isolates with 1) reduced susceptibility to ceftazidime and/or cefotaxime; 2) reduced susceptibility to cefoxitin; 3) reduced susceptibility to ceftazidime and/or cefotaxime combined with reduced susceptibility to cefoxitin. Two disk-based tests, with cloxacillin or boronic acid as inhibitor, and Etest with cefotetan-cefotetan/cloxacillin were used for phenotypic AmpC confirmation. Finally, presence of pAmpC genes was tested by multiplex and singleplex PCR.
  
  
  RESULTS
  We identified 13 pAmpC producing Enterobacteriaceae isolates among the 503 isolates (2.6%): 9 CMY-2, 3 DHA-1 and 1 ACC-1 type in E. coli isolates. The sensitivity and specificity of reduced susceptibility to ceftazidime and/or cefotaxime in combination with cefoxitin was 97% (33/34) and 90% (289/322) respectively. The disk-based test with cloxacillin showed the best performance as phenotypic confirmation method for AmpC production.
  
  
  CONCLUSIONS
  For routine phenotypic detection of pAmpC the screening for reduced susceptibility to third generation cephalosporins combined with reduced susceptibility to cefoxitin is recommended. Confirmation via a combination disk diffusion test using cloxacillin is the best phenotypic option. The prevalence found is worrisome, since, due to their plasmidal location, pAmpC genes may spread further and increase in prevalence.
authors.affiliation: Medical Microbiology and Infection Control, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: E Ascelijn
authors.initials: EA
authors.lastname: Reuland
authors.affiliation: Department of Medical Microbiology and Infectious Diseases, Erasmus MC, Rotterdam, The Netherlands.
authors.forename: John P
authors.initials: JP
authors.lastname: Hays
authors.affiliation: Department of Medical Microbiology and Infectious Diseases, Erasmus MC, Rotterdam, The Netherlands.
authors.forename: Denise M C
authors.initials: DM
authors.lastname: de Jongh
authors.affiliation: Medical Microbiology and Infection Control, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Eman
authors.initials: E
authors.lastname: Abdelrehim
authors.affiliation: Department of Medical Microbiology and Infection Control, Amphia Hospital, Breda, The Netherlands.
authors.forename: Ina
authors.initials: I
authors.lastname: Willemsen
authors.affiliation: Medical Microbiology and Infection Control, VU University Medical Center, Amsterdam, The Netherlands; Department of Medical Microbiology and Infection Control, Amphia Hospital, Breda, The Netherlands.
authors.forename: Jan A J W
authors.initials: JA
authors.lastname: Kluytmans
authors.affiliation: Medical Microbiology and Infection Control, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Paul H M
authors.initials: PH
authors.lastname: Savelkoul
authors.affiliation: Medical Microbiology and Infection Control, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Christina M J E
authors.initials: CM
authors.lastname: Vandenbroucke-Grauls
authors.affiliation: Medical Microbiology and Infection Control, VU University Medical Center, Amsterdam, The Netherlands; Laboratory for Medical Microbiology and Public Health, Hengelo, The Netherlands; Medical Microbiology and Infection Control, Ziekenhuisgroep Twente, Almelo, The Netherlands.
authors.forename: Nashwan
authors.initials: N
authors.lastname: al Naiemi
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D015373:Bacterial Typing Techniques; D002439:Cefotaxime / Q000494:pharmacology; D015313:Cefotetan / Q000494:pharmacology; D002440:Cefoxitin / Q000494:pharmacology; D002442:Ceftazidime / Q000494:pharmacology; D003023:Cloxacillin / Q000494:pharmacology; D052978:Disk Diffusion Antimicrobial Tests; D004755:Enterobacteriaceae / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics / Q000302:isolation & purification; D004756:Enterobacteriaceae Infections / Q000188:drug therapy* / Q000453:epidemiology / Q000382:microbiology; D006801:Humans; D009426:Netherlands / Q000453:epidemiology; D010957:Plasmids; D015995:Prevalence; D018440:beta-Lactam Resistance / Q000235:genetics*; D001618:beta-Lactamases / Q000235:genetics* / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D015313:Cefotetan; D002440:Cefoxitin; D002442:Ceftazidime; C048795:AmpC beta-lactamases; D001618:beta-Lactamases; D002439:Cefotaxime; D003023:Cloxacillin