Plasmid determined β lactamase indistinguishable from the chromosomal β lactamase of Escherichia coli

Abstract

A plasmid, derived from a naturally occurring strain of Proteus mirabilis, conferred resistance to cephalosporins, apparently mediated by a β lactamase indistinguishable from that determined by the chromosomal gene of E. coli K 12. There was evidence for a recombination event between the wild type plasmid and a defective F factor (Fsp) in the E. coli K 12 culture in which it was stored.