title: Outer membrane protein change combined with co-existing TEM-1 and SHV-1 beta-lactamases lead to false identification of ESBL-producing Klebsiella pneumoniae.
abstract: Nine isolates of Klebsiella pneumoniae, obtained from one colonized and eight bacteraemic patients on a paediatric ward, were shown to be identical by PFGE, indicating an outbreak. Screening for extended-spectrum beta-lactamase (ESBL) production using the double-disc synergy test, Etest for ESBLs and agar diffusion tests indicated ESBL production. The isolates showed reduced susceptibility to cefotaxime but not to other third-generation cephalosporins. Molecular studies revealed production of TEM-1 and SHV-1 but no ESBLs were identified. Deficiency in expression of an outer membrane protein (OmpK35) was also observed. These observations led us to postulate that the extremely low level of OmpK35 expression and the co-existence of TEM-1 and SHV-1 resulted in an increased MIC of cefotaxime and the false designation of the isolates as ESBL producers. All the infected infants were treated with either third-generation cephalosporins alone or multiple antibiotics including a third-generation cephalosporin, and recovered and were discharged without sequelae.
authors.affiliation: Department of Clinical Pathology, Lin-Kou Medical Center, Chang Gung Memorial Hospital, Taipei 11529, Taiwan.
authors.forename: T L
authors.initials: TL
authors.lastname: Wu
authors.forename: L K
authors.initials: LK
authors.lastname: Siu
authors.forename: L H
authors.initials: LH
authors.lastname: Su
authors.forename: T L
authors.initials: TL
authors.lastname: Lauderdale
authors.forename: F M
authors.initials: FM
authors.lastname: Lin
authors.forename: H S
authors.initials: HS
authors.lastname: Leu
authors.forename: T Y
authors.initials: TY
authors.lastname: Lin
authors.forename: M
authors.initials: M
authors.lastname: Ho
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001425:Bacterial Outer Membrane Proteins / Q000032:analysis*; D003227:Conjugation, Genetic; D003428:Cross Infection / Q000453:epidemiology; D016172:DNA Fingerprinting; D004196:Disease Outbreaks; D004352:Drug Resistance, Microbial / Q000235:genetics; D006801:Humans; D007710:Klebsiella Infections / Q000453:epidemiology*; D007711:Klebsiella pneumoniae / Q000187:drug effects / Q000201:enzymology* / Q000302:isolation & purification; D008826:Microbial Sensitivity Tests; D016133:Polymerase Chain Reaction; D013624:Taiwan / Q000453:epidemiology; D001618:beta-Lactamases / Q000302:isolation & purification*
chemical_list: D000900:Anti-Bacterial Agents; D001425:Bacterial Outer Membrane Proteins; C054882:beta-lactamase PIT-2; D001618:beta-Lactamases; C034413:beta-lactamase TEM-1