Plasmid-borne blaSHV genes in Klebsiella pneumoniae are associated with strong promoters.
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.
Turner
Mark S
MS
Institute of Heath and Biomedical Innovation, Queensland University of Technology, Musk Ave., Kelvin Grove, QLD 4059, Australia.
Andersson
Patiyan
P
Bell
Jan M
JM
Turnidge
John D
JD
Harris
Tegan
T
Giffard
Philip M
PM
D004251:DNA Transposable Elements; D020869:Gene Expression Profiling; D006801:Humans; D007710:Klebsiella Infections / Q000382:microbiology; D007711:Klebsiella pneumoniae / Q000201:enzymology* / Q000302:isolation & purification; D008969:Molecular Sequence Data; D010957:Plasmids; D011401:Promoter Regions, Genetic; D001618:beta-Lactamases / Q000096:biosynthesis* / Q000235:genetics*
D004251:DNA Transposable Elements; D001618:beta-Lactamases