title: Molecular characterization of extended-spectrum beta-lactamases and its correlation with clinical laboratory standards institute interpretive criteria for disk diffusion susceptibility testing in enterobacteriaceae isolates in Thaialnd.
abstract: We performed extended-spectrum beta-lactamase (ESBL) phenotypic testing and molecular characterization of three ESBL genes (TEM, SHV and CTX-M) and susceptibility testing by Clinical Laboratory Standards Institute (CLSI) disk diffusion method against three cephalosporins (ceftriaxone, ceftazidime, cefepime) and a cephamycin (cefoxitin) among 128 Thai Escherichia coli and 84 Thai Klebsiella pneumoniae clinical isolates. ESBL production was discovered in 62% of E. coli and 43% of K. pneumoniae isolates. All isolates susceptible to ceftriaxone were ESBL-negative. Nearly all isolates non-susceptible to ceftriaxone, ceftazidime and cefepime produced ESBL; the presence of CTX-M genes in the isolates correlated with a ceftriaxone non-susceptible phenotype. Thirty-nine of 83 isolates (47%) of ceftazidime-susceptible E. coli and 50 of 99 isolates (50.5%) of cefepime-susceptible E. coli were ESBL-producing. SHV-type beta-lactamase genes were more prevalent among K. pneumoniae than E. coli isolates. CTX-M was the major ESBL gene harbored by ESBL-producers in both E. coli and K. pneumoniae isolates. Non-CTX-M ESBL-producers were found only among K. pneumoniae isolates. This study reveals an increase in ESBL-producing Enterobacteriaceae among Thai isolates and demonstrates gaps in the current CLSI disk diffusion susceptibility guidelines; it indicates the results of ceftazidime and cefepime disk diffusion susceptibility testing using CLSI criteria should be interpreted with caution.
authors: Division of Infectious Diseases and Tropical Medicine, Department of Medicine, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand.
authors: Teerawit
authors: T
authors: Tangkoskul
authors: Surapee
authors: S
authors: Tiengrim
authors: Supiluck
authors: S
authors: Onsomang
authors: Naratchaphan
authors: N
authors: Pati
authors: Nalinee
authors: N
authors: Aswapokee
authors: Visanu
authors: V
authors: Thamlikitkul
authors: Methee
authors: M
authors: Chayakulkeeree
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology / Q000592:standards; D002511:Cephalosporins / Q000494:pharmacology / Q000592:standards; D002513:Cephamycins / Q000494:pharmacology / Q000592:standards; D052978:Disk Diffusion Antimicrobial Tests / Q000379:methods*; D004755:Enterobacteriaceae / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D006801:Humans; D007711:Klebsiella pneumoniae / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D062346:Molecular Medicine / Q000379:methods; D012015:Reference Standards; D013785:Thailand; D001618:beta-Lactamases / Q000235:genetics / Q000494:pharmacology* / Q000592:standards
chemical_list: D000900:Anti-Bacterial Agents; D002511:Cephalosporins; D002513:Cephamycins; D001618:beta-Lactamases