Part II. The “Coconut” or “Carbolic” Taint. A Study of the Causal Organism and the Factors Governing its Spore-Formation

Extract

The characters are given of the organism causing the “coconut” or “carbolic” taint of commercial sterilised milk. Although certain similarities with B. novus (Plectridium novum) Huss are shown to exist, the organism remains unidentified and the question of its identity has been reserved for a subsequent paper.

In laboratory culture the organism exists in a stable vegetative form which has resisted all efforts to induce it to sporulate. Under commercial conditions, on the other hand, it occurs in a spore form in the bottles of tainted sterilised milk.

Propagated by ordinary laboratory methods, the spore form is rapidly replaced by a vegetative race. Five serial transplants are sufficient to bring about this transformation.

Sporulation can be induced and maintained indefinitely if sporing cultures are heated at 100°C. for 30 minutes at the time of inoculation. The function of the heating process appears to be the destruction of a growth product inhibitory to the germination of the spores. This substance is associated with the growth of the vegetative form and its presence in unheated cultures is inhibitory to the germination of the spores.

Spore formation takes place at temperatures below 22°C., the spore cycle occupying 3 days at 22°C., 6 days at 15°C., and 15 days at 5°C. At higher temperatures, e.g. 30 and 37°C., it is inhibited and the normal process is replaced by an abortive effort at spore formation. The optimum temperature for the propagation of the spores is 22°C.