Submitted to: Journal of Rapid Methods and Automation in Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/27/2009
Publication Date: 12/1/2009
Citation: Tu, S., Uknalis, J., Paoli, G., He, Y., Gehring, A.G. 2009. Production of Shiga-like toxins by Escherichia coli O157:H7: Effects of other bacteria and analogues of quorum sensing molecules. Journal of Rapid Methods and Automation in Microbiology.17(4):420-437. Interpretive Summary: The Centers for Disease Control have estimated that E. coli O157:H7 bacteria cause 73,000 cases of serious illness and 61 deaths in the United States each year. The illness has been associated with the Shiga-like toxins (SLTs) secreted by the bacteria. Thus, there is a need to develop sensitive, specific and rapid detection of the bacteria and their SLTs under various environmental conditions. Using the new biosensor assay, we found that the production of SLTs was regulated by the presence of other bacteria. We also found that certain chemicals involved in the cell communication could lower the production of SLTs. This information is valuable for researchers to develop practical conditions for assaying the presence of SLTs in complex food matrices.
Technical Abstract: During the growth of Escherichia coli O157:H7, shiga-like toxins are produced. Time course studies indicated that the accumulation of toxins in the medium occurrs mainly at the stationary phase of cell growth. The growth of E. coli O157:H7 in culture media was not significantly affected by the presence of other bacteria, e.g., E. coli K12, E. coli B6, Salmonella and Pseudomonus, even at high ratios. However, the production of Shiga-like toxins by E. coli O157:H7 could be reduced by certain other bacteria, e.g., E. coli K-12, Pseudomonas aeruginosa but not Pseudomonas putida. The similar lowering effects by other background bacteria on the toxin production were also observed by comparing the results between regular and irradiated ground beef. The presence of analogues of quorum sensing molecules such as homoserine lactone (HSL) and indole, in general decreased the production of toxins by E. coli O157:H7. This decrease could be partially reversed by the presence of sub-optimal concentrations of antibodies. The results suggested that toxin production by E. coli O157:H7 was modulated by complex environmental conditions.