Production and characterization of exotoxin(s) of Shigella dysenteriae type 1

Abstract

A semicontinuous fermenter system was developed in which broth culture filtrates of Shigella dysenteriae type 1 yielded substantial amounts of exotoxin. Biologic activity of the exotoxin was characterized by means of three assays: the rabbit ileal loop for fluid evocation (enterotoxicity), mouse lethality after parenteral injection (neurotoxicity), and HeLa cell toxicity in vitro (cytotoxicity). Although the culture filtrate was highly active, disc electrophoresis revealed that the toxin is a minor component of the mixture of proteins in the crude preparation, and that the minor representation contrasts with the relative prominence of exotoxins in cultures of other bacteria, such as Vibrio cholerae, Corynebacterium diphtheriae, and Clostridium tetani. Filtrate toxin, when purified by isoelectric focusing in polyacrylamide gel, was found to contain two toxic moieties. One was resolvable as a single band with an isoelectric joint (pI) of 7.25, a molecular weight of 72,000, and all three types of biological activity. The second moiety was isoelectric at pH 6.00, contained two subcomponents, and further contrasted with the pI 7.25 toxin by being more cytotoxic while being devoid of enteroneurotoxic activity.