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Title:   Author  item
                                            Sharma, Vijayitem
                                            Bearson, Bradley

                                                         - *Brad*item
                                            Casey, Thomas
  Submitted to: Meeting Abstract
                                    Publication Type: Abstract Only
                                    Publication Acceptance Date: 3/3/2010
                                    Publication  Date: 4/20/2010
                                    Citation: Sharma, V.K., Bearson, B.L., Casey, T. 2010. Hha Represses Biofilm Formation in Escherichia coli O157:H7 by Affecting the Expression of Flagella and Curli Fimbriae[abstract]. American Society for Microbiology Meeting. p350.Interpretive Summary:
                                Technical Abstract: Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is a zoonotic pathogen that produces a broad-spectrum of diarrheal illnesses in infected humans. Although the genetic and molecular mechanisms enabling EHEC O157:H7 to produce characteristic adherence on epithelial cells are well characterized, the genes and the genetic regulation required for the formation of biofilms on abiotic surfaces are not fully understood.  In this study, we demonstrate that the formation of biofilms in EHEC O157:H7 strain 86-24, which does not express Type 1 fimbriae (an important constituent of biofilms in E. coli K12 strains), is highly repressed compared to an isogenic strain with a hha deletion. Further analysis revealed that hha deletion reduced the expression of the flagellar gene fliC but increased the expression of csgA, encoding curlin of curli fimbriae. The reduced expression of fliC and increased csgA expression correlated with decreased bacterial motility and an increased capacity to bind the dye Congo red, as well as, to produce large quantities of biofilms, respectively. In trans complementation by a cloned copy of hha, restored bacterial motility and decreased biofilm production in the hha mutant strain to the levels comparable to that observed for the parent strain.  This data provides strong evidence that EHEC O157:H7 is capable of producing biofilms under conditions that would limit its motility and allow increased expression of adhesive structures like the curli fimbriae. Whether the Hha-mediated repression of biofilm formation occurs independently, requiring only Hha interactions with the promoters controlling the expression of flagellar and curli regulons, or occurs in conjunction with additional genetic factors (HN-S) or pathways (quorum sensing signaling pathway encoded by qseBC or the metabolic pathway required for the indole production) impacting the expression of flagella or curli fimbriae or both, remains to be investigated.


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