ampD homologs in biotypes of Yersinia enterocolitica: Implications in regulation of chromosomal AmpC-type cephalosporinases.

Inducible 'AmpC-type' chromosomal cephalosporinases have been reported to be differentially expressed in different biotypes of Yersinia entercolocolitica. AmpD amidases are key regulators of the expression of ampC genes in Y. entercolocolitica as their inactivation results in hyper production of AmpC. To understand the differences in regulation of ampC expression in different biotypes of Y. enterocolitica, characteristics of ampD homologs were studied in strains of Y. enterocolitica belonging to five biotypes namely 1A, 1B, 2, 3 and 4. Our results indicated that the mechanisms which regulate expression of ampC might differ in different biotypes. While a three-step regulation mechanism seemed to be functional in biotypes 2, 3 and 4, a two-step regulation mechanism using other AmiD like proteins might be functional in biotypes 1A and 1B. The existence of ampD homolog(s)-mediated expression of ampC in other members of the family Enterobacteriaceae may provide further credence to our findings.