Abstract

Bacterial resistance mechanisms to the antibiotics known as β‐lactams, which include the penicillins and cephalosporins, can take several forms but frequently involve the production of β‐lactamases from either plasmid‐ or chromosomally‐encoded loci. Gram negative bacteria express a β‐lactamase from evolutionarily related chromosomal ampC genes. Genetic analysis of both inducible and constitutively expressed AmpC β‐lactamases provide insights into the mechanisms regulating production of the enzyme. Evolutionary relationships between the genes of different species are discussed, as well as the regulatory mechanisms that in both laboratory mutants and clinical isolates lead to overproduction of β‐lactamase.