The pathogenesis of footrot in sheep with reference to proteases of Fusiformis nodosus

Abstract

Preparations of cultures of Fusiformis nodosus, the causal organism of footrot in sheep, were tested for their ability to digest substrates of dermal and epidermal tissues. The preparations did not hydrolyse hyaluronic acid, chondroitin sulphate, or collagen. Weak elastase activity was demonstrated. Enzyme preparation 1 obtained from the supernatant fluid of liquid cultures during growth of F. nodosus, and enzyme preparation 2 obtained after growth had ceased, digested powdered sheep hoof in the presence of cysteine. Enzyme preparation 1 possessed two pH optima for hoof digestion, at pH values of 7.6 and about 10.5. Enzyme preparation 2 also possessed two optima, at pH 8.2 and at about 10.5. Hoof digestion by either enzyme preparation was enhanced by 4M urea with cysteine, particularly at pH 10.0.

Hoof digestion by enzyme preparations 1 and 2 was not inhibited by iodoacetamide. Hoof pretreated with potassium thioglycollate or with performic acid was digested by both enzyme preparations 1 and 2 in the absence of cysteine. For these reasons, cysteine was considered to react with the substrate rather than with the enzymes. The digestion of preparations of amorphous, fibrous, and reduced and carboxymethylated hoof protein, for which cysteine was not required, supported this view, and indicated that cysteine exposed hoof proteins to the digestive action of F. nodosus proteolytic enzymes by sulphydryl transfer.

Enzyme preparations 1 and 2 also disintegrated frozen sections of sheep hoof. This effect was greater at pH 10.0 than at 8.0 and in the presence of cysteine.

When enzyme preparations 1 and 2 were injected into the skin of sheep at pH 8.0 and 10.0 together with cysteine, ulcers were produced in 24–48 hr. These were similar to the ulceration of the epidermis of the hoof in footrot.