Submitted to: Federation of European Microbiological Societies Microbiology Letters
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/6/2004
Publication Date: 2/1/2005
Citation: Sharma, V.K., Carlson, S.A., Casey, T. 2005. Hyperadherence of an hha mutant of Escherichia coli O157:H7 is correlated with enhanced expression of LEE-encoded adherence genes. Federation of European Microbiological Societies Microbiology Letters. 243(1):189-196. Interpretive Summary: Escherichia coli O157:H7, a Shiga toxin-producing E. coli (STEC), is by far the most prevalent in human disease and has been associated with the most important foodborne outbreaks in the USA and Canada. Most human E. coli O157:H7 infections are caused by consumption of contaminated foods (ground beef, milk, and produce) and water. Cattle are generally considered the major reservoir for these disease-causing bacteria. E. coli O157:H7 colonizes intestine of cattle and is secreted into feces of these animals. These bacteria can survive in feces for months and are the major source for the transmission of these bacteria to other cattle and humans. Understanding of factors that enable E. coli O157:H7 to colonize cattle intestine will help design vaccines and/or vaccine strains for reducing E. coli O157:H7 prevalence and shedding in cattle. In the present study, we describe that the absence of the hha gene has a significant effect on the ability of E. coli O157:H7 to adhere to tissue-cultured mammalian cells. The increased adherence of E. coli O157:H7 to tissue-cultured cells was accompanied by significant increases in the level of factors that have been shown to promote adherence and colonization in cattle. The current study provides us an important tool for investigating the potential use of the hha lacking E. coli O157:H7 strain as a vaccine for reducing E. coli O157:H7 colonization and shedding in cattle. This information would also be of potential use to other scientists, Food Safety and Inspection Service, veterinary biologics, and the pharmaceutical industry.
Technical Abstract: Enterohemorrhagic Escherichia coli (EHEC) O157:H7 virulence factors, specifically those conferring intimate adherence to and formation of attaching and effacing lesions (A/E) on host cells, are encoded by a horizontally acquired locus of enterocyte effacement (LEE). Expressions of several LEE-encoded genes, which are organized into operons LEE1 through LEE5, are under the positive regulation of ler, the first gene in the LEE1 operon. We have recently demonstrated that EHEC O157:H7 lacking hha exhibited greater than a 10-fold increase in ler expression and that the repression of ler results from the binding of Hha to the ler promoter. In this report, we show that an hha mutant of EHEC O157:H7 exhibited increased adherence to Hep-2 cells, had increased transcriptional activities of LEE1 through LEE5 as determined by RT-PCR assays, and expressed LEE5::lac transcriptional fusion at levels that were several-fold higher than that expressed by the parental hha**+ strain. These results demonstrate that hha is an important regulatory component of the cascade that governs the expression of LEE1-LEE5 and the resulting ability of EHEC O157:H7 to intimately adhere to host cells.