Factors affecting plaque formation by Candida albicans infecting the chick chorio-allantoic membrane.

The numbers of plaques formed by Candida albicans in replicate inocula on the chick chorio--allantoic membrane (CAM) was not related to the size of the inocula. Washing the CAM with saline 1 h after inoculation recovered only 10% of the inoculum. After 5 h cells could not be recovered by washing. By contrast, counts on serial dilutions of homofenised eggs after inoculation showed that the organisms had retained their viability within the egg. Failure of the inoculum to recover in spite of survival of the organisms appears to be due to adhesion of the inoculum to the CAM and cohesion of the inoculum to form clumps. We suggest that clumps of a least 20 organism are needed to stimulate the CAM to proliferate and produce visible plaques. The clumping is random and this accounts for the variation in the number of plaques. The production of plaques by the CAM may depend on the clumping of a sufficient number of organisms to produce a critical concentration of extra-cellular enzymes which aid penetration of the CAM by the invading hyphae. The relevance of this to the lesions of mucocutaneous candidiasis has been considered.