Use of Phenotypic MicroArray to Determine Culture Conditions that Regulate the Production of Shiga Toxin in Different Escherichia coli Pathotypes

Introduction: Shiga toxin-producing Escherichia coli (STEC) include many serotypes with different levels of pathogenicity to humans. The toxins produced by STEC (Shiga toxin 1 and 2), and their subtypes, are one of their major pathogenic attributes. Ultraviolet light, certain antibiotics, and low iron levels have been shown to affect toxin production, but little is known about how other growth and environmental factors regulate the stxgenes.

Purpose: To compare the effect of different environmental factors on the expression of Shiga toxin among a broad spectrum of STEC to help determine which strains are more pathogenically relevant.

Methods: We are using the Phenotypic MicroArray (PM) developed by Biolog to determine the effect of more than 1,200 culture conditions on the production of Shiga toxin.  These conditions include different metabolites such as: carbon, phosphorus, nitrogen and sulfur sources, as well as, antibiotics, chemicals, pH and ionic conditions. The changes in Shiga toxin production were determined quantitatively from PM plate supernatants, by their cytotoxic effect on Vero cells.

Results: Our preliminary results show that the growth conditions that regulate Shiga toxin in E. coli O157:H7 and the 2011 German outbreak strain E. coli O104:H4 are similar, but some differences have been observed and need to be pursued further. Several carbon sources showed an effect on toxin production including arabinose, ribose, lyxose, xylose and glucosamine to name few. Also, the role on induction of a variety of antibiotics, some consistent with previous studies like ciprofloxacin and others new was identified.

Significance: These studies can lead to the identification of conditions that will allow for a more specific detection and identification of STEC in the food supply.