Journal
JOURNAL OF ANTIMICROBIAL CHEMOTHERAPY
Volume 64, Issue 5, Pages 960-964Publisher
OXFORD UNIV PRESS
DOI: 10.1093/jac/dkp338
Keywords
K. pneumoniae; ESBLs; SHV; high resolution melting; expression
Funding
- National Health and Medical Research Council, Australia [390121]
- Menzies School of Health Research
- Queensland University of Technology
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Background: Extended-spectrum beta-lactamases (ESBLs) belonging to the SHV family remain a major cause of ESBL-positive phenotypes in Klebsiella pneumoniae. The bla(SHV) gene is a normal constituent of the K. pneumoniae chromosome. However, most ESBL-encoding bla(SHV) genes found in K. pneumoniae are plasmid borne. The objective was to determine the contribution of promoter variants to the expression of plasmid-borne bla(SHV) genes. Methods: K. pneumoniae clinical isolates were analysed for the presence of IS26 insertions characteristic of plasmid-borne bla(SHV), and differences in their bla(SHV) promoter sequences and expression levels. A high resolution melting (HRM)-based method for rapid promoter analysis was developed. Results: An IS26 insertion characteristic of the plasmid-borne bla(SHV-1)/bla(SHV-2)/bla(SHV-5) family was 100% linked to a promoter mutated in the -10 region, a mutation previously only found on the chromosome. The mutation was shown by real-time reverse transcriptase PCR to be associated with increased bla(SHV) expression. Conclusions: Plasmid-borne bla(SHV) is associated with strong promoters. It is likely that an SHV-dependent ESBL-positive phenotype requires both a strong promoter and a coding sequence mutation. An HRM assay can indicate bla(SHV) expression.
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