Mechanism and stability of hyperproduction of the extended-spectrum beta-lactamase SHV-5 in Klebsiella pneumoniae.

Abstract

Some isolates of SHV-5 beta-lactamase-producing Klebsiella pneumoniae K2 from a single-strain outbreak of cross-infection produced approximately five-fold more beta-lactamase than others. We investigated three possible genetic mechanisms of this hyperproduction: the presence of a more powerful promoter, an increase in plasmid copy number or an amplification of the gene on a plasmid. No differences between low and high beta-lactamase producers were detected in the promoter region of the SHV-5 beta-lactamase gene, which closely resembled that of SHV-2. SHV-5 beta-lactamase production was encoded on a low copy number plasmid, but DNA-DNA hybridization with an SHV-specific probe detected a higher gene dose in hyperproducers. The beta-lactamase hyperproduction was unstable on repeated subculture, with a reduction of about 75% after 100 generations. Hyperproducing mutants of a low-producing Klebsiella and its Escherichia coli K-12 transconjugants could be selected in vitro at a frequency of 10(-5) to 10(-6) and these variants had an increased SHV-5 beta-lactamase gene copy number on low copy number plasmids. We conclude that hyperproduction of the extended-spectrum beta-lactamase was caused by gene amplification that could be easily lost or gained in vitro. Since the change to hyperproduction occurred at a high frequency and hyperproducers showed increased resistance to many beta-lactams and beta-lactam/beta-lactamase inhibitor combinations, we suspect that these variants may readily be selected in patients during antibiotic therapy.

• Authors: X Xiang, K Shannon, G French
• Journal: The Journal of antimicrobial chemotherapy (J Antimicrob Chemother) Vol. 40 Issue 4 Pg. 525-32 (Oct 1997) ISSN: 0305-7453 [Print] England
• PMID: 9372422 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• DNA, Bacterial
• beta-lactamase SHV-5
• beta-Lactamases

Topics

• DNA, Bacterial (chemistry)
• Enzyme Stability
• Gene Dosage
• Klebsiella pneumoniae (enzymology)
• Plasmids
• Promoter Regions, Genetic
• beta-Lactamases (biosynthesis, chemistry, genetics)