Molecular characterization of FOX-4, a new ampC-type plasmid-mediated beta-lactamase from an Escherichia coli strain isolated in Spain

A clinical strain of Escherichia coli (Ec GCE) displayed resistance to cefo xitin, cefotetan, cefotaxime, and ceftazidime. Susceptibility was not resto red by the addition of clavulanic acid. Two beta-lactamases with apparent p Is of 5.4 and 6.4 were identified; the beta-lactamase with a pI of 6.4 was transferred by conjugation and associated with a 40-kb plasmid, Analysis of the nucleotide sequence showed a new ampC beta-lactamase gene that is clos ely related to those encoding the FOX-3, FOX-2, and FOX-1 beta-lactamases b ut whose product has four novel amino acid mutations, at positions 11 (M--> T), 43 (A-->E), 233 (V-->A), and 280 (Y-->H). This first cephamycinase from Spain was named FOX-4.