Heterogeneity in ampr-ampc gene interaction in enterobacter cloacae

The ampR gene and its regulation of AmpC B-lactamase synthesis were investigated for Enterobacter cloacae 1194E, a wild-type strain producing a group A (pI 8.7) enzyme. Expression of the cloned E. cloacae 1194E ampR-ampC region was examined initially in Escherichia coli HBIOI. However, transformants showed only constitutive B-Iactamase expression. For study of enzyme expression in a more closely related host, the cloned E. cloacae 1194EampR-ampC region was transformed into E. cloacae 55, a wild-type strain producing a group B (pI 7.8) enzyme. Results indicated a functional E. cloacae 1194EampR gene that could not be transcomplemented by E. cloacae 55. A comparative analysis of ampR nucleotide and amino acid-sequence data from E. cloacae 1194E and E. cloacaeMHNI revealed related but divergent genes. Thermal induction studies of AmpC B-lactamase also indicated a difference between E. cloacae 1194E and E. cloacae 55 in ampR-ampC interaction. Thus, it appears that, in at least some strains of Enterobacter, significant intraspecies divergence of ampR has occurred. This heterogeneity in ampR would not have been detected with β-Iactamase expression studies conducted exclusively in E. coli.