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FEMS Microbiol Lett. 1999 Apr 15;173(2):459-65.

Mutations in the ampC promoter of Escherichia coli isolates resistant to oxyiminocephalosporins without extended spectrum beta-lactamase production.

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Laboratoire de Bactériologie-Virologie, Faculté de Pharmacie, Nantes, France.


Escherichia coli strains showing an increased resistance to oxyiminocephalosporins without an extended spectrum beta-lactamase production have been screened for mutations in their ampC beta-lactamase gene promoter. Mutations were found by direct sequencing of seven promoters at positions -42, -32 (box -35), -18, -1, +5, +24 (attenuator), +31 (attenuator) and +58. By using rapid and simple methods, three of these mutations (-42, -32 and +24), which could enhance transcription, were searched in 37 resistant and 25 sensitive isolates. The -42 mutation was present in 33 of the 37 promoters from the resistant isolates. The -32 and +24 mutations were present only in three and two promoters, respectively, and they were combined in the most resistant strain of the study. The +24 mutation was detected in another strain associated with a 1-bp insertion between the -35 and -10 conserved sequences. None of these mutations was detected in the ampC beta-lactamase from the sensitive isolates.

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