AN EXTENDED-SPECTRUM AMPC-TYPE BETA-LACTAMASE OBTAINED BY IN-VITRO ANTIBIOTIC SELECTION

A predictive approach was assayed to evaluate the possibility of mutan t Amp-C beta-lactamase emergence with increased substrate spectrum (in cluding new C-3' quaternary ammonium cephems). The ampC gene encoding the AmpC beta-lactamase from Enterobacter cloacae was cloned and expre ssed in an AmpC-defective strain of E. coli. After the AmpC containing strain was challenged with cefpirome, an ampC variant encoding an enz yme with increased resistance to cefpirome and cefepime was selected. In addition, this variant conferred increased resistance to penicillin s and third generation cephalosporins. The complete nucleotide sequenc e of the gene was determined. The deduced peptide sequence showed a si ngle change with respect to the wild-type gene. valine to glutamic aci d at position, 318 of the native protein (298 of the mature enzyme). T he potential emergence and spread of this type of AmpC variants among pathogens should be considered. (C) 1998 Federation of European Microb iological Societies. Published by Elsevier Science B.V. All rights res erved.