title: Detection of extended-spectrum β-lactamase in Enterobacter spp.--evaluation of six phenotypic tests.
abstract: Extended-spectrum β-lactamases (ESBL) are plasmid-mediated enzymes that hydrolyze cephalosporins and monobactams. The lack of a standard method to detect ESBL in Enterobacter spp. has led to underestimating its frequency. The aim of this study was to evaluate ESBL detection in Enterobacter spp. By the double-disk synergy test (DDST) and combined disk test (CDT) assay using cefepime, cefotaxime, and ceftazime as substrates for ESBL, plus AmpC inhibitors in different associations. A total of 83 Enterobacter spp. ESBL and 31 non-ESBL Enterobacter spp. were tested, and a cutoff point ≥3 mm was defined using a receiver operating characteristic (ROC) curve for combined disc methods. All tests showed 100% specificity. The sensitivity was 89.2% for DDST and CDT without AmpC inibitor, 90.4% in the combined disc test in Mueller-Hinton agar containing phenylboronic acid (CDT-PBAA), and 94% in the combined disc test in Mueller-Hinton agar containing cloxacillin (CDT-CLXA). Cefepime was the best substrate, mainly when AmpC inhibitors were not used. However, superior results were achieved when all cephalosporins were evaluated together. In conclusion, to improve ESBL detection in Enterobacter spp., some modifications in phenotypic tests are needed, such as to reduce the distance between the discs to 20 mm in DDST, to use a cutoff point for ≥3 mm on the CDT, and to include a cefepime disk or an inhibitor of AmpC in all tests.
authors: Hospital de Clínicas, Universidade Federal do Paraná (UFPR), Curitiba, Brazil. keitenogueira@hotmail.com
authors: Keite da Silva
authors: Kda S
authors: Nogueira-Miranda
authors: Jussara Kasuko
authors: JK
authors: Palmeiro
authors: Danieli
authors: D
authors: Conte
authors: Fernanda Valverde
authors: FV
authors: Maia
authors: Iara Taborda de Messias
authors: IT
authors: Reason
authors: Cristina Leise
authors: CL
authors: Monteiro
authors: Libera Maria
authors: LM
authors: Dalla-Costa
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000037:antagonists & inhibitors / Q000235:genetics*; D002511:Cephalosporins / Q000494:pharmacology*; D052978:Disk Diffusion Antimicrobial Tests / Q000379:methods / Q000592:standards*; D004338:Drug Combinations; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics*; D004754:Enterobacter / Q000187:drug effects / Q000235:genetics* / Q000302:isolation & purification; D004756:Enterobacteriaceae Infections / Q000188:drug therapy* / Q000382:microbiology; D006801:Humans; D010957:Plasmids / Q000235:genetics; D012372:ROC Curve; D012680:Sensitivity and Specificity; D017422:Sequence Analysis, DNA; D065093:beta-Lactamase Inhibitors; D001618:beta-Lactamases / Q000235:genetics*
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D002511:Cephalosporins; D004338:Drug Combinations; D065093:beta-Lactamase Inhibitors; C048795:AmpC beta-lactamases; D001618:beta-Lactamases