Characterisation of CMY-4, an AmpC-type plasmid-mediated β-lactamase in a Tunisian clinical isolate of Proteus mirabilis

A strain of Proteus mirabilis resistant to β-lactams, including cefoxitin, was isolated from the urine of a woman from Tunisia. Its antibiotic susceptibility pattern and that of the Escherichia coli transconjugant suggested the presence of an AmpC-type β-lactamase. Two bands of β-lactamase activity (pI 5.4 and 9.2) were detected by isoelectric focusing. The nucleotide sequence of the gene encoding the AmpC-type enzyme was determined. The deduced amino acid sequence was 98-99% identical to CMY-3 and to those of the plasmid-mediated AmpC-type β-lactamases originated from Citrobacter freundii and 97% identical to the chromosome-encoded β-lactamase of a Tunisian clinical isolate of C. freundii. This enzyme differs from CMY-2 by one substitution (Arg for Trp at position 221) and from CMY-3 by two substitutions (Glu for Gly at position 42 and Ser for Asn at position 363) and we propose the denomination CMY-4. Copyright (C) 1998 Federation of European Microbiological Societies.