title: Comparison of the double-disk, combined disk, and Etest methods for detecting metallo-beta-lactamases in gram-negative bacilli.
abstract: Three phenotypic methods for detecting metallo-beta-lactamases (MBLs) in gram-negative bacilli were tested on 60 MBL producers and 155 MBL nonproducers. The 2-mercaptopropionic acid double-disk potentiation method using ceftazidime and cefepime with and without clavulanate was found to be most sensitive (100%). The combined disk method depends on comparing the zones given by disks containing a beta-lactam with and without ethylenediaminetetraacetic acid. Various drug combinations were tested, and the best results were obtained with imipenem for Pseudomonas species and Acinetobacter baumannii, ceftazidime-clavulanate for Klebsiella pneumoniae, and cefepime-clavulanate for Enterobacter cloacae and Citrobacter freundii. The overall sensitivity of the combined disk method was 86.7%. The Etest (AB BIODISK, Solna, Sweden) method using imipenem- ethylenediaminetetraacetic acid strips detected imipenem-resistant MBL-producing isolates only, resulting in a sensitivity of 36.7%. Our data suggest that the double-disk and combined disk tests are acceptable methods for MBL detection in both imipenem-resistant and imipenem-susceptible isolates.
authors.affiliation: Department of Pathology, National Cheng Kung University Hospital, Tainan, Taiwan. jingjou@mail.ncku.edu.tw
authors.forename: Jing-Jou
authors.initials: JJ
authors.lastname: Yan
authors.forename: Jiunn-Jong
authors.initials: JJ
authors.lastname: Wu
authors.forename: Shu-Huei
authors.initials: SH
authors.lastname: Tsai
authors.forename: Chin-Luan
authors.initials: CL
authors.lastname: Chuang
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001431:Bacteriological Techniques; D000077723:Cefepime; D002442:Ceftazidime / Q000494:pharmacology; D002511:Cephalosporins / Q000494:pharmacology; D019818:Clavulanic Acid / Q000494:pharmacology; D017077:Culture Media, Conditioned; D024881:Drug Resistance, Bacterial; D006090:Gram-Negative Bacteria / Q000201:enzymology / Q000302:isolation & purification*; D006801:Humans; D015378:Imipenem; D008826:Microbial Sensitivity Tests; D012680:Sensitivity and Specificity; D001618:beta-Lactamases / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D002511:Cephalosporins; D017077:Culture Media, Conditioned; D019818:Clavulanic Acid; D015378:Imipenem; D000077723:Cefepime; D002442:Ceftazidime; D001618:beta-Lactamases