Inducible Expression of the Chromosomal cdiA from Citrobacter diversus NF85,Encoding an Ambler Class A β-Lactamase,Is under Similar Genetic Control to the Chromosomal ampC,Encoding an Ambler Class C Enzyme,from Citrobacter freundii OS60

ABSTRACT

This study aimed to characterize the molecular basis of β-lactamase induction in Citrobacter diversus. The chromosomal β-lactamase encoding region from C. diversus, strain NF85, was cloned and expressed in Escherichia coli. The cloned region was sequenced and open-reading frames encoding a class A β-lactamase, designated cdiA, and a putative LysR-type transcriptional regulator protein, divergently transcribed from the β-lactamase gene and designated cdiR, were identified. The nucleotide sequence of the NF85 cdiA was identical to that of the published 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. freundii ampCR intergenic region. A putative CdiR binding motif was identified in the cdiAR intergenic region. The cloned cdiAR region was inducible in E. coli strains SN03 and HfrH. The inducible phenotype was dependent on the E. coli ampD and ampG gene products. We conclude that the molecular basis of inducible cdiA expression in C. diversus is similar to that of C. freundii ampC.