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Factors affecting plaque formation by Candida albicans infecting the chick chorio-allantoic membrane
Abstract:
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.
Insights
Candida albicans plaque formation on the chick chorioallantoic membrane (CAM) depends on organism clumping, not inoculum size. Clumps of at least 20 cells are needed to trigger CAM proliferation and plaque development.
Area of Science:
- Microbiology
- Mycology
- Infectious Diseases
Background:
- Candida albicans is an opportunistic fungal pathogen.
- Mucocutaneous candidiasis is a common infection caused by C. albicans.
- The chick chorioallantoic membrane (CAM) is a model for studying host-pathogen interactions.
Purpose of the Study:
- To investigate the relationship between Candida albicans inoculum size and plaque formation on the CAM.
- To understand the mechanisms underlying C. albicans adhesion and survival on the CAM.
- To determine the minimum number of C. albicans cells required for plaque induction.
Main Methods:
- Inoculation of C. albicans onto the CAM.
- Washing the CAM to assess inoculum recovery.
- Serial dilution counts of homogenized eggs to determine organism viability.
- Microscopic examination of CAM for plaque formation.
Main Results:
- Plaque formation was not correlated with inoculum size.
- Only 10% of the inoculum was recovered by washing after 1 hour; none after 5 hours.
- C. albicans remained viable within the egg despite poor recovery from the CAM surface.
- Organism adhesion and clumping were identified as reasons for poor recovery.
- A minimum of 20 C. albicans cells per clump appeared necessary for plaque stimulation.
Conclusions:
- C. albicans plaque formation on the CAM is dependent on cell clumping, not initial inoculum size.
- Clumping facilitates the development of a critical concentration of extracellular enzymes, aiding hyphal invasion.
- These findings provide insights into the pathogenesis of mucocutaneous candidiasis.