The beta toxin of Clostridium welchii Type B, Wilsdon, in relation to the production of a vaccine against lamb dysentery

Abstract

Evidence is provided to prove the specificity of the flocculation test used as a tool for assaying the beta fraction of Cl. welchii Type B toxin and its corresponding antitoxin. The separation from Cl. welchii Type B ("1930 strain") of variants which differ in the production of toxin and mucoid material is described. A medium and method of cultivation are described by means of which a maximum yield of 560 Lf per mi. of beta toxin was obtained. By using a sodium acetate-acetic acid buffer system a purified beta toxin containing 7,396 Lf per mg. P.N. was produced. The keeping qualities of beta toxin under varying conditions were determined. The toxoiding of beta toxin (both crude and purified) was investigated. The stability of beta toxoid was determined. A study was made of alum precipitation of beta toxoid with varying concentrations of potash alum at different pH levels. APT was proved to be a better antigen than liquid toxoid. II was proved experimentally that sheep, immunized with two doses of APT, each containing from 6·25 Lf to 200 Lf and separated by an interval of two weeks, would have a mean circulating antitoxin titre of about 50 units per ml. one week after the second stimulus. As a result of a series of experiments in which the booster effect produced by beta toxoid was investigated the conclusion was reached that the essential requirement for an effective booster response is a solid basic immunity. When the latter is present the dose and nature of the booster injection are of secondary importance. It was proved that APT containing 6·25 Lf beta toxoid per dose could be used as a primary, secondary and booster stimulus for the prevention of lamb dysentery.