Se- quencing and analysis of four new Enterobacter ampD alleles. Antimicrob. Agents Chemother

Sequences of ampD genes from wild-type, temperature-sensitive, and stably derepressed mutants of the wild-type strain Enterobacter cloacae 029 and the hyperinducible strain E. cloacae 1194E were determined and compared with the ampD gene of the wild-type strain E. cloacae 14. Seventy nucleotide differences were found between the wild-type sequences, resulting in 13 amino acid changes. The deduced amino acid changes do not correspond to published AmpC regulation mutations and expand the number of known mutations leading to altered AmpC b-lactamase expression in members of the family Enterobacteriaceae. The production of the Bush group 1 (1), chromosomally encoded AmpC b-lactamase of gram-negative bacteria such as Enterobacter cloacae and Citrobacter freundii is normally induc-ible. Three genes, in addition to ampC (the structural gene for the b-lactamase), which are known to participate in the induc-tion process have been identified. These genes are ampR, which encodes a transcriptional regulator; ampD, which en-codes an enzymatic repressor of induction; and ampG, which encodes a transmembrane protein which possibly functions a