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J Antimicrob Chemother. 2004 Jun;53(6):1076-80. Epub 2004 May 5.

Citrobacter koseri and Citrobacter amalonaticus isolates carry highly divergent beta-lactamase genes despite having high levels of biochemical similarity and 16S rRNA sequence homology.

Author information

1
Bristol Centre for Antimicrobial Research and Evaluation, Department of Pathology & Microbiology, University of Bristol, School of Medical Sciences, University Walk, Bristol BS8 1TD, UK.

Abstract

OBJECTIVES:

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

METHODS:

beta-Lactamase and 16S rRNA genes were amplified by PCR and sequenced by standard methods. beta-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 beta-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 beta-lactamase, Cko, constitutively at low levels. The cko and cdiA beta-lactamase genes share <45% identity.

CONCLUSIONS:

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

PMID:
15128725
DOI:
10.1093/jac/dkh235
[Indexed for MEDLINE]

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