JAC Advance Access originally published online on September 12, 2009
Journal of Antimicrobial Chemotherapy 2009 64(5):960-964; doi:10.1093/jac/dkp338
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Original research |
Plasmid-borne blaSHV genes in Klebsiella pneumoniae are associated with strong promoters
1 Institute of Heath and Biomedical Innovation, Queensland University of Technology, Musk Ave., Kelvin Grove, Q 4059, Australia 2 School of Land, Crop and Food Sciences, University of Queensland, St Lucia, Q 4072, Australia 3 Menzies School of Health Research, Institute of Advanced Studies, Charles Darwin University, Casuarina, Darwin, NT 0810, Australia 4 SA Pathology @ Women's and Children's Hospital, 72 King William Rd, North Adelaide, SA 5006, Australia 5 Departments of Pathology, Paediatrics and Molecular and Biomedical Sciences, Adelaide University, Adelaide, SA 5000, Australia
Received 3 May 2009; returned 17 June 2009; revised 21 August 2009; accepted 24 August 2009
* Corresponding author. Menzies School of Health Research, Building 58, Royal Darwin Hospital Campus, PO Box 41096 Casuarina, NT 0811, Australia. Tel: +61-8-89448040; Fax: +61-8-89275187; E-mail: phil.giffard{at}menzies.edu.au
Background: Extended-spectrum β-lactamases (ESBLs) belonging to the SHV family remain a major cause of ESBL-positive phenotypes in Klebsiella pneumoniae. The blaSHV gene is a normal constituent of the K. pneumoniae chromosome. However, most ESBL-encoding blaSHV genes found in K. pneumoniae are plasmid borne. The objective was to determine the contribution of promoter variants to the expression of plasmid-borne blaSHV genes.
Methods: K. pneumoniae clinical isolates were analysed for the presence of IS26 insertions characteristic of plasmid-borne blaSHV, and differences in their blaSHV 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 blaSHV-1/blaSHV-2/blaSHV-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 blaSHV expression.
Conclusions: Plasmid-borne blaSHV 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 blaSHV expression.
Keywords: K. pneumoniae , ESBLs , SHV , high resolution melting , expression