INDUCIBLE EXPRESSION OF THE CHROMOSOMAL CDIA FROM CITROBACTER-DIVERSUS NF85, ENCODING AN AMBLER CLASS-A BETA-LACTAMASE, IS UNDER SIMILAR GENETIC-CONTROL TO THE CHROMOSOMAL AMPC, ENCODING AN AMBLER CLASS-C ENZYME, FROM CITROBACTER-FREUNDII OS60

This study aimed to characterize the molecular basis of beta-lactamase induction in Citrobacter diversus. The chromosomal beta-lactamase enc oding region from C. diversus, strain NF85, was cloned and expressed i n Escherichia coli. The cloned region was sequenced and open-reading f rames encoding a class A beta-lactamase, designated cdiA, and a putati ve LysR-type transcriptional regulator protein, divergently transcribe d from the beta-lactamase gene and designated cdiR, were identified, T he nucleotide sequence of the NF85 cdiA was identical to that of the p ublished C. diversus ULA27 ampC sequence. A putative helix-turn-helix DNA-binding motif was located at the N-terminus of CdiR, and homology with enterobacterial AmpR proteins was noted. CdiR was demonstrated to bind to the C. diversus cdiAR intergenic region but not to the C. fre udii ampCR intergenic region. A putative CdiR binding motif was identi fied in the cdiAR intergenic region. The cloned cdiAR region was induc ible in E. coli strains SNO3 and HfrH. The inducible phenotype was dep endent on the E. coli ampD and ampG gene products. We conclude that th e molecular basis of inducible cdiA expression in C. diversus is simil ar to that of C. freundii ampC.