Shiga Toxin Production by Different Escherichia coli Serotypes Grown under High Osmolarity Conditions

Introduction: Shiga Toxin-producing E. coli (STEC) include 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 environmental factors affect growth and toxin production among STEC.

Purpose: The purpose of this study is to assess various phenotypic conditions defined through the Biolog platform.

Methods: The Phenotypic Microarray (PM) was used in this study. We focused on the PM-9 plate to determine the effect of different osmolyte/ionic conditions on the growth and toxin production among STEC. PM-9 plates were inoculated following manufactures instructions, and data was analyzed using Biolog software to determine growth kinetics.  The presence of Shiga Toxin from PM-9 filtrates was determined by ELISA.

Results: Our preliminary results show a significant variability on the survival of different STEC to salt (NaCl). The 2011 German outbreak strain E. coli O104:H4, is highly osmotolerant and survives well up to 6% NaCl (W/V). However, E. coli O157:H7 strain EDL933 cannot grow above 3%, and EC4045, from the spinach outbreak, grows well up to 4%. We also observed differences on the Shiga Toxin produced under these stress conditions among the different serotypes. Shiga Toxin was detected from E. coli O104:H4 cultures grown on media supplemented with 6% NaCl.

Significance: Salt is widely used as food preservative in meat processing. Although the effect of salt in the survival and toxin production of E. coli O157:H7 is well known, little work has been done on other STEC serotypes that can also present a threat to public health.