[The mutation and the selection of inactivating enzymes against antibiotic resistances]

The genes coding for inducible beta-lactamase production from S. aureus pI258 showed constitutive expression in E. faecalis. These findings suggest that constitutive beta-lactamase production in E. faecalis is due to not only to the absence of functional regulatory genes but to some factors as well. However, hypothetical model for control of the expression of inducible ampC genes in Grm-negative bacteria is slightly different to that of S. aureus and E. faecalis. The muropeptide GlcNac-anhMurNac-tripeptide, tetrapeptide and pentapeptide are transport into the cytoplasm through AmpG. Intracellular accumulation of GlcNac-anhMurNac-tripeptide as the results of the presence of the beta-lactam antibiotics or of anhMurNac-tripeptide as the results of inactivation of ampD triggers production of E. cloacae AmpC beta-lactamase. The muropeptides presumably bind to the ampR, the transcriptional regulator, and convert it into an activator for ampC expression.