Differential efficiency of induction of various lambdoid prophages responsible for production of Shiga toxins in response to different induction agents.

Shiga toxin-producing Escherichia coli (STEC) is a group of pathogenic strains responsible for bloody diarrhea and hemorrhagic colitis, with often severe complications. Shiga toxins are the main factors causing the phathogenicity of STEC. Production of these toxins depends on the presence of stx1 and stx2 genes, which are located on lambdoid prophages, and their expression is stimulated upon prophage induction. Therefore, a transition of the phage genome from the prophage state to an extrachromosomal genetic element, and its further propagation, is crucial for the pathogenic effects. However, our knowledge on specific conditions for induction of these prophages in bacteria occurring in human intestine is very limited. In this report we present results of our studies on five different phages, originally occurring in STEC strains, in comparison to bacteriophage lambda. We found that efficiencies of induction of prophages and their further development vary considerably in response to different induction agents. Moreover, efficiency of progeny phage production might be modulated by other factors, like temperature or bacterial growth rate. Therefore, it is likely that pathogenicity of different STEC strains may be significantly different under specific conditions in their natural habitats.