title: Survey of CTX-M-3 extended-spectrum beta-lactamase (ESBL) among cefotaxime-resistant Serratia marcescens at a medical center in middle Taiwan.
abstract: Thirty-four clinical isolates of Serratia marcescens nonsusceptible to cefotaxime were collected from a medical center in middle Taiwan. Confirmatory tests for extended-spectrum beta-lactamases (ESBLs) by cefotaxime and ceftazidime +/- clavulanic acid using Etest ESBL Screen identified only one ESBL producer; the remaining 33 isolates revealed nondeterminable results, because of off-scale minimum inhibitory concentration (MIC) levels for cefotaxime +/- clavulanic acid. Agar microdilution method using broader MIC ranges confirmed 21 ESBL-producers and one non-determinable result, achieving a highly predicting value compared to golden standard by PCR and DNA sequencing analysis, which identified 22 (65%) isolates containing blaCTX-M-3 genes. Only one strain carried concurrent CTX-M-3 and SHV-5 conferring high-level MICs to both cefotaxime (128 microg/mL) and ceftazidime (64 microg/mL). Other enzymatic mechanisms, such as chromosome-encoded AmpC including a novel SRT-2 enzyme, may confer resistance to cefotaxime on the remaining 12 isolates without ESBL bla genes. Thus, it is unreliable to predict the resistance mechanism by antibiogram, and current Etest ESBL Screen tests. Our study highlights expanding efforts to detect ESBLs in S. marcescens are urgently needed in Taiwan.
authors.affiliation: Department of Microbiology, Institute of Medical Science, China Medical University, Taichung City, Taiwan.
authors.forename: Lii-Tzu
authors.initials: LT
authors.lastname: Wu
authors.forename: Mei-Fen
authors.initials: MF
authors.lastname: Tsou
authors.forename: Hwa-Jene
authors.initials: HJ
authors.lastname: Wu
authors.forename: Hui-En
authors.initials: HE
authors.lastname: Chen
authors.forename: Yin-Ching
authors.initials: YC
authors.lastname: Chuang
authors.forename: Wen-Liang
authors.initials: WL
authors.lastname: Yu
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001483:Base Sequence; D002439:Cefotaxime / Q000494:pharmacology*; D003428:Cross Infection / Q000188:drug therapy / Q000382:microbiology; D004269:DNA, Bacterial / Q000032:analysis; D003625:Data Collection; D024881:Drug Resistance, Bacterial; D005260:Female; D006785:Hospitals, University; D006801:Humans; D008297:Male; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D012680:Sensitivity and Specificity; D016868:Serratia Infections / Q000175:diagnosis / Q000188:drug therapy; D012706:Serratia marcescens / Q000187:drug effects* / Q000302:isolation & purification; D013624:Taiwan; D001618:beta-Lactamases / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; C417271:beta-lactamase CTX-M-3; D001618:beta-Lactamases; D002439:Cefotaxime