Candida albicans and Candiasis
|
Candida albicans and Candiasis |
Candida
albicans
is a human pathogenic fungus, responsible for more than half of
the secondary infections emanating in AIDS, or other immunocompromised
patients. Although this organism has been known since ages (to the times
of Aristotle) the exact mechanism of infection is still elusive. While
the genetic makeup of Candida
albicans
is similar to that of Saccharomyces
cerevisiae, the former is
characterized by its intrinsic resistance
to a wide spectrum of antifungal drugs.
Candidiasis
is one of the major secondary infections prevalent among patients
undergoing long term drug therapies, transplants, or treatments relying
on suppressing the immune system. Among AIDS patients, the most
troublesome secondary infection is Candidiasis, and a major focus of
AIDS researchers is to stop or control such secondary infections. The
causative organism, Candida albicans, is a human commensal, but
certain factors are known to turn commensal into pathogen, resulting in
superficial as well as deep-seated mycoses. While superficial lesions
(white lesions on the skin/epithelia) are easily accessible and can be
treated by topical application of antifungals, deep-seated mycoses are
difficult to counter. All living tissues can be infected by Candida,
but the most common manifestations are on vaginal and mucosal surfaces,
commonly known as "thrush" (soor in German, afta
in Spanish and Italian, le meguet in French, nhova in
Zimbabwe).
Candida
albicans is a polymorphic yeast which
can exist in different morphological forms like the unicellular yeast (blastospore
or blastoconidia), pseudohyphae, where a chain
of cells is formed due to inefficient separation of mother and daughter
cells after cell division or long filamentous hyphae where each
nuclei is separated by septa, but no indentation at the site septation.
The bud-hypha transition is critical in pathogenesis, and has been known
to be influenced by a variety of factors including nutritional status,
temperature, pH of the medium, presence of serum or macrophages, trace
elements, etc. While serum, high temperature (37o C), neutral
pH, high CO2:O2 ratio and nutrient poor media
induce hyphal growth; low temperature, air, acidic pH (4-6) and enriched
media support blstospore phase. Amino acids (nitrogen source) and sugars
(carbon source) have also been associated with the bud-hypha transition.
Further
Reading: