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

Thea S.B. Kjeldsen, Martin Overgaard, S.S. Nielsen, Valeria Bortolaia, Lotte Jelsbak, Morten Sommer, Luca Guardabassi, John Elmerdahl Olsen

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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).
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.
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.
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.
TidsskriftJournal of Antimicrobial Chemotherapy
StatusUdgivet - 2015
Udgivet eksterntJa

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