AI-2-like acttivity mediated E. coli O157:H7 survival and virulence gene expression in the presence of ground beef extracts

Abstract

Cell-to-cell communication, termed quorum sensing, mediated by AI-2 like activity, has been reported to regulate the expression of a variety of genes in E. coli O157:H7. A previous study in our laboratory has shown that foods can contain compounds that can interfere with AI-2 signaling. The underlying hypothesis of our studies is that the autoinducer molecules such as AI-2 are involved in the virulence and survival of enteric bacterial pathogens on food and food ingredients. The influence of AI-2 like activity on the survival and expression of virulence genes (hha and yadK) in E.coli O157:H7 was studied when the organism was stored in different types of ground beef extracts such as: cooked, uncooked, and autoclaved. The survival was observed at refrigeration temperature, while change in gene expression was studied using real-time PCR. Higher survival was observed in the cell exposed to cell free supernatant (CFS) containing AI-2 like molecules, compared to the one which was exposed to heat degraded AI-2 like molecules. The survival of cells was higher when exposed to cooked ground beef extracts compared to uncooked and autoclaved ground beef extracts. Similarly, higher gene expressions of both hha and yadK genes were observed in cells that were exposed to cooked beef extract samples as compared to samples that wereuncooked or autoclaved. About a 2 fold higher gene expression for both hha and yadK gene was observed when cells were subjected to cooked ground beef extracts in the presence of AI-2 like molecules compared to the ones exposed to uncooked ground beef extracts in the presence of AI-2 like molecules. Likewise, 3-fold higher gene expression was observed for cells exposed to cooked ground beef extracts compare to autoclaved ground beef extracts in the presence of AI-2 like molecules. The results suggest that the survival and virulence of enteric bacterial pathogens such as E.coli O157:H7 can be influenced by the interaction of food components and autoinducers such as AI-2, that are involved in bacterial cell communications.