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

Escherichia coli strains showing an increased resistance to oxyiminocephalo sporins without an extended spectrum beta-lactamase production have been sc reened for mutations in their ampC beta-lactamase gene promoter. Mutations were found by direct sequencing of seven promoters at positions -42, -32 (b ox -35), -18, -1, +5, +24 (attenuator), +31 (attenuator) and +58. By using rapid and simple methods, three of these mutations (-42, -32 and +24), whic h could enhance transcription, were searched in 37 resistant and 25 sensiti ve isolates. The -42 mutation was present in 33 of the 37 promoters From th e resistant isolates. The -32 and +24 mutations were present only in three and two promoters, respectively, and they were combined in the most resista nt strain of the study. The +24 mutation was detected in another strain ass ociated 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 se nsitive isolates, (C) 1999 Federation of European Microbiological Societies . Published by Elsevier Science B.V. All rights reserved.