Tel. (+ 45) 45 25 25 06; Fax (+ 45) 45 93 28 09. Summary It is now apparent that microorganisms undergo sig-nificant changes during the transition from planktonic to biofilm growth. These changes result in phenotypic adaptations that allow the formation of highly orga-nized and structured sessile communities, which pos-sess enhanced resistance to antimicrobial treatments and host immune defence responses. Escherichia coli has been used as a model organism to study the mechanisms of growth within adhered communities. In this study, we use DNA microarray technology to examine the global gene expression profile of E. coli during sessile growth compared with planktonic growth. Genes encoding proteins involved in adhe-sion (type 1 fimbriae) and, in particular, autoaggrega-tion (Antigen 43) were highly expressed in the adhered population in a manner that is consistent with current models of sessile community develop-ment. Several novel gene clusters were induced upon the transition to biofilm growth, and these included genes expressed under oxygen-limiting conditions, genes encoding (putative) transport proteins, puta-tive oxidoreductases and genes associated with enhanced heavy metal resistance. Of particular inter-est was the observation that many of the genes altered in expression have no current defined func-tion. These genes, as well as those induced by stresses relevant to biofilm growth such as oxygen and nutrient limitation, may be important factors that trigger enhanced resistance mechanisms of sessile communities to antibiotics and hydrodynamic shear forces.
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