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J Antimicrob Chemother. 2015 Jan;70(1):62-70. doi: 10.1093/jac/dku332. Epub 2014 Sep 1.

CTX-M-1 β-lactamase expression in Escherichia coli is dependent on cefotaxime concentration, growth phase and gene location.

Author information

1
Department of Veterinary Disease Biology, Faculty of Health and Medical Sciences, University of Copenhagen, 1870 Frederiksberg C, Denmark.
2
Department of Clinical Biochemistry and Pharmacology, Odense University Hospital, 5000 Odense, Denmark Institute of Clinical Research, University of Southern Denmark, 5000 Odense C, Denmark.
3
Department of Large Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, 1870 Frederiksberg C, Denmark.
4
Department of Systems Biology, Technical University of Denmark, 2800 Lyngby, Denmark Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, 2970 Hørsholm, Denmark.
5
Department of Veterinary Disease Biology, Faculty of Health and Medical Sciences, University of Copenhagen, 1870 Frederiksberg C, Denmark jeo@sund.ku.dk.

Abstract

OBJECTIVES:

Knowledge about the regulatory mechanisms of CTX-M β-lactamase-encoding genes in Escherichia coli is limited. The objectives of this study were to determine the growth response of CTX-M-1-producing E. coli exposed to cefotaxime and to investigate how blaCTX-M-1 expression at mRNA and protein levels is influenced by cefotaxime concentration, growth phase and gene location (chromosome versus plasmid).

METHODS:

Two isogenic E. coli strains, MG1655/CTX-M-1 and MG1655/IncI1/CTX-M-1, containing blaCTX-M-1 on the chromosome and on a wild-type IncI1 plasmid, respectively, were constructed and the MIC of cefotaxime was determined. Growth of the two strains was studied in the presence of increasing concentrations of cefotaxime ranging from 0 to 512 mg/L. The levels of mRNA and protein in different growth phases and at different cefotaxime concentrations were studied by qPCR and selected-reaction-monitoring MS, respectively.

RESULTS:

The MICs of cefotaxime were 168 and 252 mg/L for MG1655/CTX-M-1 and MG1655/IncI1/CTX-M-1, respectively. Both strains displayed a prolonged lag phase when exposed to cefotaxime. The mRNA of blaCTX-M-1 and CTX-M-1 protein levels increased in the presence of high cefotaxime concentrations and varied with growth phase. Higher mRNA expression levels were detected for MG1655/CTX-M-1 compared with MG1655/IncI1/CTX-M-1, but a higher protein level was found for MG1655/IncI1/CTX-M-1 compared with MG1655/CTX-M-1, the latter corresponding well with the higher MIC for this strain.

CONCLUSIONS:

blaCTX-M-1 mRNA expression and CTX-M-1 protein levels were dependent on cefotaxime concentration, growth phase and gene location. These results provide insight into the expression of cephalosporin resistance in CTX-M-1-producing E. coli, improving our understanding of the relationship between antimicrobial therapy and the expression of resistance mechanisms.

KEYWORDS:

ESBLs; antimicrobial resistance; regulation

PMID:
25182062
DOI:
10.1093/jac/dku332
[Indexed for MEDLINE]

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