Submitted to: Federation of European Microbiological Societies Microbiology Letters
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/20/2007
Publication Date: 6/16/2007
Citation: Dowd, S.E. 2007. Escherichia coli O157:H7 gene expression in the presence of the catecholamine norepinephrine. Federation of European Microbiological Societies Microbiology Letters. 273:214-223. Interpretive Summary: Stress in animals is thought to enhance the shedding of foodborne pathogens which endanger the food supply. If the animal is shedding more pathogens, there is a higher risk of adulteration of food. When animals are stressed, they secrete a hormone called norepinephrine into their intestines. This hormone has been shown to enhance the pathogenicity of bacteria such as Escherichia coli O157:H7 which is a major contaminant of ground beef. We have run microarray experiments which determine exactly how this stress hormone causes the bacteria to become more dangerous. The results can now be used to design treatments that reduce or stop these changes from occurring. Now that we know that intense stress can make pathogens more dangerous, we can also focus on methods to reduce stress in livestock.
Technical Abstract: To examine the effects of the catecholamine norepinephrine (NE) on the expression of virulence factors in Escherichia coli O157:H7, the clinical-type isolate EDL933 (ATCC 43895) was grown in the presence or absence of NE. An in-vitro culture system made up of low initial innocula and a serum-SAPI based medium, as described by Lyte et al , was employed. After 5 hrs of exposure to NE, treatment cultures and control cultures (not exposed to NE) were harvested and their RNA purified and subsequently utilized for microarray analyses. Results indicated that there was a dramatic increase in the expression of virulence factor transcripts including stx1 stx2, eae, and tir, as well as transcripts involved in iron binding and iron transport. Conversely, there were comparative repressions of several iron acquisition, flagellar biosynthesis, and phage shock protein-related transcripts in the presence of NE. There were also a wide variety of transcriptional regulatory genes that were comparatively induced or repressed in the presence or absence of NE, including repression of qseA and induction of qseB, which have been noted to be genes involved in quorum sensing. The results corroborate many of the previous findings detailed in the literature. Expression profiles are discussed in relation to the microarray results which could elucidate additional LEE induction mechanisms, promote better understanding of the genetic control of iron acquisition in relation to NE, and elucidate novel stress responses.