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

A strain of Proteus mirabilis resistant to beta-lactams, including cefoxiti n, was isolated from the urine of a woman from Tunisia. Its antibiotic susc eptibility pattern and that of the Escherichia coil transconjugant suggeste d the presence of an AmpC-type beta-lactamase. Two bands of beta-lactamase activity (pI 5.4 and 9.2) were detected by isoelectric focusing. The nucleo tide 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 beta-lactamases originated from Citrobacter freundii and 97% identical to the chromosome-encoded beta-lactamase of a Tu nisian clinical isolate of C. freundii. This enzyme differs from CMY-2 by o ne substitution (Arg for Trp at position 221) and From CMY-3 by two substit utions (Glu for Gly at position 42 and Ser for Asn at position 363) and we propose the denomination CMY-4. (C) 1998 Federation of European Microbiolog ical Societies. Published by Elsevier Science B.V. All rights reserved.