β-lactam induction of colanic acid gene expression in Escherichia coli

An unexpected observation led us to examine the relationship between beta-lactam exposure and synthesis of colonic acid capsular polysaccharide in Escherichia coli. Strains containing a cps-lacZ transcriptional fusion were challenged with antibiotics having various modes of action, and gene expression was detected by a disk-diffusion assay and in broth cultures. The cps genes were induced by a subset of beta-lactams but not by agents inhibiting protein synthesis or DNA replication, indicating that cps expression was specific and not due to stresses accompanying cell death or by a general inhibition of peptidoglycan synthesis. A narrow concentration just below the MIC triggered cps expression in liquid culture, suggesting the response may be triggered by near-lethal levels of antibiotic. Because colanic acid is important for maturation of biofilm architecture, antibiotics that increase its synthesis might exacerbate the formation or persistence of biofilms. (C) 2003 Federation of European Microbiological Societies. Published by Elsevier B.V. All rights reserved.