Enhanced production of natural shiga toxin by overexpressing A subunit of Stx2e in Stx2e-producing Escherichia coli isolated in South Korea

Abstract

This study explored the optimal culture conditions for maximizing shiga toxin production in Stx2e-producing Escherichia coli (STEC) 150229, isolated from porcine edema disease (ED), with the goal of preparing a Stx2e toxoid vaccine candidate. High cytotoxicity was observed for this strain [tissue culture cytotoxic dose 50% (10⁴ TCCD₅₀/100 µl)] from 48 h after incubation. Stx2e was overexpressed by transforming pStx2e A into STEC 150229, resulting in the production of recombinant Stx2e A/B complex combined with intrinsic Stx2e B. The enhanced production of Stx2e was evaluated based on the level of cytotoxicity against Vero cells. The highest cytotoxicity (10⁵ TCCD₅₀/100 µl) was observed with the samples of recombinant Stx2e A/B complex eluted with 500 mM imidazole at 48 h of incubation. In conclusion, the recombinant Stx2e A protein forms an active protein complex with the intrinsic Stx2e B component from STEC 150229, producing high levels of shiga toxin.