Dissemination of CTX-M-Type extended-spectrum β-lactamase genes to unusual hosts

A Citrobacter amalonaticus and a Morganella morganii producing the CTX-M-1 extended-spectrum beta-lactamase (ESBL) were isolated from an area where this enzyme is now widespread in Escherichia coli. This is the first report of CTX-M-1 in the former species. In both cases the ESBL determinant was possibly acquired by these unusual hosts in vivo, after coinfection with E. coli strains carrying conjugative plasmids encoding CTX-M-1.