Influence of Autoinducer-2 (AI-2) and Beef Sample Extracts on E. coli O157:H7 Survival and Gene Expression of Virulence Genes yadK and hhA

Bacterial cell-to-cell communication is mediated by autoinducer (AI) molecules such as AI-2 and has been reported to regulate gene expression in Escherichia coli O157:H7. We have previously shown that ground beef contains compounds that can inhibit sensing of AI-2 like activity. The hypothesis of this study was that AI-2 activ- ity observed in conditioned medium (CM) will enhance E. coli O157:H7 survival and expression of virulence genes, whereas compounds inhibitory (such as those present in ground beef extracts) to AI-2 activity will negate these ef- fects. E. coli O157:H7 luxS mutant strain VS 94 (incapable of synthesizing AI-2) was employed in these studies. The survival of this enteric bacterial pathogen as a function of AI-2 activity and the presence of AI-2 inhibitory com- pounds was studied at 4 ◦ C. The number of survivors in the presence of AI-2 was significantly higher compared to the absence of AI-2, and the addition of ground beef extracts to conditioned medium negated the influence of AI- 2 activity. Autoinducer AI-2 upregulated selected genes virulence genes (yadK ,a ndhha), whereas the ground beef extract reversed the effect of AI-2 on the expression of the selected genes.