Molecular basis of beta-lactamase induction in bacteria

Inducible synthesis of 3-lactamases was first described for the gram-positive organism Bacillus licheniformis (6) and was followed by similar reports for Bacillus cereus (1) and Staphylococcus aureus (7).Unlike the ,-lactamases of gram- positive bacteria, the majority of ,B-lactamases of gram- negative bacteria are expressed constitutively (9).However, in 1967, Hennessey (10) described an inducible P-lactamase of Enterobacter cloacae that is now known to be encoded by the chromosomal ampC gene (23, 31).Inducible expression of ampC-like genes has subsequently been reported for Citrobacterfreundii, Pseudomonas aeruginosa, and various other gram-negative bacteria (2, 15, 23, 31, 36, 40).Staphylococcal ,3-lactamases are predominantly plasmid encoded, extracellular enzymes, most of which are inducible (29).Early studies by Richmond (35) led to the proposal that inducible P-lactamase synthesis in S. aureus was under