Characterisation of CTX-M and AmpC genes in human isolates of Escherichia coli identified between 1995 and 2003 in England and Wales

CTX-M and AmpC genes in human isolates of Escherichia coli, their genetic environment and their host plasmids were examined. Isolates (n = 103) were selected based on resistance (minimum inhibitory concentration (MIC) ≥ 1 μg/mL) to ceftriaxone and cefotaxime. Polymerase chain reaction (PCR) and sequencing identified 29 isolates containing blaCTX-M-15, 1 each of blaCTX-M-2 (a strain originating from Israel) and blaCTX-M-40, 20 isolates containing blaCMY-7, 4 blaCMY-2 and 1 blaCMY-21. This is the first study of plasmid-mediated AmpC genes in E. coli in the UK. Eleven cefoxitin-resistant, AmpC PCR-negative isolates had ampC promoter region mutations. All blaCTX-M-15 and 24 of 25 blaCMY genes were associated with an ISEcp1-like element. The blaCTX-M-2 was located in an orf513-bearing class 1 integron. Plasmid restriction digests suggest transfer of genes between different plasmid backbones.