title: Use of several inducer and substrate antibiotic combinations in a disk approximation assay format to screen for AmpC induction in patient isolates of Pseudomonas aeruginosa, Enterobacter spp., Citrobacter spp., and Serratia spp.
abstract: Two-hundred consecutive, single patient isolates of Enterobacter spp., Serratia spp., Citrobacter spp., and Pseudomonas aeruginosa were evaluated for AmpC production using a variety of inducer-substrate antibiotic combinations in a disk approximation format. The combinations examined included cefoxitin-piperacillin, imipenem-cefotaxime, imipenem-ceftazidime, imipenem-piperacillin-tazobactam, and imipenem-cefoxitin. All isolates were also screened for the presence of extended-spectrum beta-lactamase (ESBL) activity. In total, 85.5% of isolates were shown to be inducible for the production of AmpC by one or more inducer/substrate combinations and 11% of all isolates were stably derepressed for the expression of AmpC. Of all of the combinations, imipenem/piperacillin-tazobactam provided the greatest sensitivity (97.1%). All combinations were 100% specific when a positive test was observed. Given this background among these organisms in our institution, it is reasonable to develop an antibiotic reporting strategy that favors the selection of agents for therapy of these organisms that do not serve as labile substrates of AmpC.
authors.affiliation: Departments of Pathology and Immunology, Washington University School of Medicine, 660 S. Euclid Ave., Box 8118, St. Louis, MO 63110, USA. dunne@wustl.edu
authors.forename: W Michael
authors.initials: WM
authors.lastname: Dunne
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Hardin
mesh_terms: D000900:Anti-Bacterial Agents / Q000378:metabolism / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000096:biosynthesis*; D002954:Citrobacter / Q000187:drug effects / Q000201:enzymology; D004359:Drug Therapy, Combination; D004754:Enterobacter / Q000187:drug effects / Q000201:enzymology; D004790:Enzyme Induction; D006090:Gram-Negative Bacteria / Q000187:drug effects* / Q000201:enzymology*; D006801:Humans; D008403:Mass Screening; D008826:Microbial Sensitivity Tests / Q000295:instrumentation / Q000379:methods; D011550:Pseudomonas aeruginosa / Q000187:drug effects / Q000201:enzymology; D012705:Serratia / Q000187:drug effects / Q000201:enzymology; D001618:beta-Lactamases / Q000096:biosynthesis*; D047090:beta-Lactams / Q000378:metabolism / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D047090:beta-Lactams; C048795:AmpC beta-lactamases; D001618:beta-Lactamases