Inhibition of development of Shiga toxin-converting bacteriophages by either treatment with citrate or amino acid starvation

Objectives: Shiga toxin–producing Escherichia coli (STEC) are pathogenic strains, whose virulence depends on induction of Shiga toxin–converting prophages and their subsequent lytic development. We explored which factors or conditions could inhibit development of these phages, potentially decreasing virulence of STEC. Materials and Methods: Lytic development of Shiga toxin–converting bacteriophages was monitored after mitomycin C-provoked prophage induction under various conditions. Phage DNA replication efficiency was assessed by measurement of DNA amount in cells using quantitative polymerase chain reaction. Results: We demonstrated that the use of citrate delayed Shiga toxin–converting phage development after prophage induction. This effect was independent on efficiency of prophage induction and phage DNA replication. However, an excess of glucose reversed the effect of citrate. Amino acid starvation prevented the phage development in bacteria both able and unable to induce the stringent response. Conclusions: Lytic development of Shiga toxin–converting bacteriophages can be inhibited by either the presence of citrate or amino acid starvation. We suggest that the inhibition caused by the latter condition may be due to a block in prophage induction or phage DNA replication or both. Applications: Our findings may facilitate development of procedures for treatment of STEC-infected patients