PRODUCTION OF SHIGA-LIKE TOXINS BY ESCHERICHIA COLI O157 : H7: EFFECTS OF OTHER BACTERIA AND ANALOGS OF QUORUM SENSING MOLECULES

Abstract

ABSTRACT

Accompanied with the growth of Escherichia coli O157 : H7, there was a production of Shiga-like toxins by this pathogenic bacterium. Time-course studies indicated that the accumulation of toxins in the medium occurred 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 K-12, E. coli B6, Salmonella and Pseudomonas, 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. These lowering effects by other background bacteria on the toxin production were also observed in experiments using regular and irradiated ground beef. The presence of analogs 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 subinhibitory concentrations of antibiotics. The complex nature of the control of Shiga toxin production is discussed.

PRACTICAL APPLICATIONS

The toxic effects of pathogenic bacterium E. coli O157 : H7 are related to the production of Shiga-like toxins by the pathogen. Current studies on the influence of environmental factors such as cell density, presence of other bacteria, chemicals and food components indicated a complex influence on the production of Shiga-like toxins by E. coli O157 : H7. The observation that the presence of certain other bacteria could lower the ability of E. coli O157 : H7 to produce the toxins was of particular interest. The analyses of the results suggested several practical possibilities to lower the production of the toxins, and thus, the health risk of the pathogen to the general public.