Journal Article

<i>Citrobacter koseri</i> and <i>Citrobacter amalonaticus</i> isolates carry highly divergent β-lactamase genes despite having high levels of biochemical similarity and 16S rRNA sequence homology

Sarah Underwood and Matthew B. Avison

in Journal of Antimicrobial Chemotherapy

Published on behalf of British Society for Antimicrobial Chemotherapy

Volume 53, issue 6, pages 1076-1080
Published in print June 2004 | ISSN: 0305-7453
Published online June 2004 | e-ISSN: 1460-2091 | DOI: http://dx.doi.org/10.1093/jac/dkh235
Citrobacter koseri and Citrobacter amalonaticus isolates carry highly divergent β-lactamase genes despite having high levels of biochemical similarity and 16S rRNA sequence homology

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Objectives: Isolates previously identified as Citrobacter diversus are now known as Citrobacter koseri. We measured sequence variation at the β-lactamase structural gene among a group of clinical isolates originally identified as C. diversus by API 20E profiling.

Methods: β-Lactamase and 16S rRNA genes were amplified by PCR and sequenced by standard methods. β-Lactamase induction was attempted in liquid-grown cultures using cefoxitin. Nitrocefin hydrolysis assays were performed using a spectrophotometer.

Results: Analysis of 16S rRNA gene sequences showed that Citrobacter spp. isolates with an inducible β-lactamase gene, cdiA, closely related to ‘C. koseri ’ NF85 and ULA27 are actually Citrobacter amalonaticus. C. koseri isolates, whose identities were confirmed by 16S rRNA sequencing, produce a class A β-lactamase, Cko, constitutively at low levels. The cko and cdiA β-lactamase genes share <45% identity.

Conclusions: We have confirmed that cko is a β-lactamase gene carried by C. koseri, and that isolates previously identified as ‘C. koseri ’, but carrying the cdiA β-lactamase gene are C. amalonaticus. Thus, β-lactamase-gene-specific PCR may provide a valuable tool to differentiate these biochemically homogeneous Citrobacter species.

Keywords: Keywords: Citrobacter, β-lactamases, phylogenetics, induction

Journal Article.  3154 words.  Illustrated.

Subjects: Medical Oncology ; Critical Care

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