Cloning and sequencing of the gene encoding the AmpC beta-lactamase of Morganella morganii

The chromosomal beta-lactamase gene of a clinical isolate of Morganella morganii was cloned in Escherichia coli and sequenced. The beta-lactamase had a pI of 7.4 and conferred a typical AmpC susceptibility pattern. The insert obtained was found to encode a protein of 379 amino acids. Its deduced amino acid sequence revealed it to be a class C beta-lactamase: 39-56% identity with chromosomal AmpC beta-lactamases of Serratia marcescens, Yersinia enterocolitica, Citrobacter freundii, Enterobacter cloacae and Escherichia coli; and 37-56% identity with plasmid-mediated beta-lactamases (MOX-1, CMY-1, FOX-1, ACT-1, LAT-1, BIL-1 and CMY-2). The ampC gene was linked to a gene only part of which (450 bp) was cloned homologous to the regulatory ampR genes of chromosomal class C beta-lactamases.