Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: October 1, 2010
Publication Date: October 4, 2010
Citation: Sharma, V.K. Regulation of Biofilm Formation in Escherichia coli O157:H7 [abstract]. 45th United States-Japan Cooperative Program in Natural Resources Panel of Animal and Avian Health Meeting. p. 16. Technical Abstract: Escherichia coli O157:H7 encodes a variety of genetic factors for adherence to epithelial cells and to abiotic surfaces. While adherence to epithelial cells culminates in the formation of characteristic attaching and effacing (A/E) lesions, adherence to abiotic surfaces represents a prelude to the formation of biofilms. Of the factors influencing biofilm formation, curli fimbriae are the most important cell surface structures used by E. coli O157:H7 to produce biofilms. The regulation of the expression of curli fimbriae is very complex and has not been completely understood. In this study, we describe that hha, the gene that also regulates the expression of enterohemolysin and production of A/E lesions, repressed biofilm formation in E. coli O157:H7 because the hha deletion mutant of this strain produced increased amounts of biofilm, which could be lowered to the level produced by the hha**+ parent strain by complementing the mutant by a plasmid-cloned copy of hha. Increased production of biofilm by the hha mutant correlated with an increased expression of the gene csgA that encodes for curli fimbriae, and an increased ability of this mutant to bind the dye Congo red, which also suggested an increased biogenesis of curli fimbriae. Interestingly the expression of fliC, the gene encoding for the major structural subunit of flagella, was reduced by several-fold in the hha mutant with concomitant reduction in its motility relative to that of the hha**+ parent strain. These differential effects of Hha on transcriptional regulation of csgA and fliC resulted from direct interactions of purified Hha with the promoters regulating the expression of these two genes. In addition, the hha mediated regulation of biofilm production appears to be independent of the QseBC quorum-sensing signaling system because the presence of epinephrine, which enhances flagellar gene expression and bacterial motility by activating the QseBC-mediated quorum-sensing, had no significant effect on the levels of biofilm production by the parent strain but caused additional increases in biofilm production in hha and hha qseC mutant strains. These results indicate that increased expression of curli fimbriae and reduced expression of flagellar genes and motility are essential for an increased production of biofilm by E. coli O157:H7.