A NOVEL CLASS-C BETA-LACTAMASE (FOX-2) IN ESCHERICHIA-COLI CONFERRINGRESISTANCE TO CEPHAMYCINS

An Escherichia coli strain resistant to a broad spectrum of beta-lacta ms, including cephamycins, was isolated from a patient suffering from urinary tract infection. A resistance plasmid (pRjlVP-7) was transferr ed from the clinical isolate to an Escherichia coli recipient. Both st rains Produce a cefoxitin-hydrolyzing beta-lactamase focusing at pi 6. 7. The phenotype was similar to that of a Klebsiella pneumoniae strain producing cephamycinase FOX-1, so primers were selected from the FOX- 1 sequence to amplify the bla gene of the transconjugant. The PCR prod uct obtained was sequenced: The percentage of identity of the deduced aminoacid sequence with sequences of other AmpC-type beta-lactamases w as 96.9% with FOX-1, 74.9% with CMY-1, and 67.7% with MOX-1. This new plasmid-mediated enzyme is most closely related to FOX-1 (11 amino aci d exchanges). We therefore propose the designation FOX-2.