Candida albicans
by Noah Strickland
Candida albicans is a dimorphic fungus. This means that that C. albicans has to different phenotypic forms, an oval shaped yeast form and a branching hyphal form. C. albicans normal habitat is the mucosal membranes of humans and various other mammals including the mouth, gut, vagina, and sometimes the skin. Normally C. albicans causes no damage and lives symbiotically with the human or animal host, even helping to breakdown minute amounts of fiber that are eaten in the host’s diet. The normal bacterial flora of the gut, mouth, and vaginal mucosa act as a barrier to the over growth of fungal infections like C. albicans. Loss of this normal flora is one of the main predisposing factors to an infection by C. albicans.
There are many ways that a C. albicans infection may occur. One is the use of antibiotics for an extended period of time to combat a pre-existent bacterial infection. Since the antibiotics used will kill only the bacteria and not any fungus this allows for C. albicans to gain a foot hold over the local mucosa that it is inhabiting, be it the gut, the mouth , the vagina or even the teeth and gums of the host. Taking substances that alter the hormone levels in the body is another common way that C. albicans can gain an advantage over the normal bacterial flora. Two common substances are steroids and birth control pills. These both act to alter the host’s body chemistry in a way that is favorable to the over growth of C. albicans. If the host is immunocompromised to begin with as in the case of AIDS patients or organ transplant receivers that are on immunosupresive drugs C. albicans infections are very prominent. A common symptom among AIDS patients is oral thrush, where there is a huge over population of C. albicans on the back of the hosts tongue, it appears as white speckles.
When C. albicans becomes pathogenic, or switches it’s phenotype to the hyphal form to invade the host cell epithelium, be it the mouth or the gut or the vagina; these infections are superficial and can usually be treated with common anti-fungal agents like fluconazole, diflucan, azole-related anti fungal drugs, amphotericin B, fungizone ( I think this is the same as amphotericin B). However in severely immunocompromised individuals like transplant patients or AIDS patients C. albicans can become systemic. That is the fungus will travel through the blood stream and infect any major organ it can. When C. albicans has become systemic it is almost always fatal because of the similarity between the host cells and the fungus, and the lack of a reliable anti fungal drug.
Common symptoms of an oral C. albicans infection include burning pain, altered taste, difficulty swallowing and whitish spots on the gums and tongue ( common only below CD4 cell counts of 500). Common symptoms of a vaginal C. albicans infection include itching, swelling, and a thick and odorous discharge. Vaginal fungal infections are usually associated with pregnancy. It is also estimated that every women in her life time will have had a C. albicans infection
C. albicans has also displays many virulence factors. These include a large number of adhesins that help the fungus stick to the epithelium of the host cell. These adhesins include many agglutinin-like sequences(ALS’s), an integrin-like protein and an Hwp-1 protein that targets host transgutaminases which actually cross-link C. albicans to host cells. C. albicans also secretes hydrolytic enzymes that are assumed to damage host cells which in turn provides nutrients for the fungus. C. albicans also secrets apartyl proteinases and lipases which are interestingly turned on and off during the progression of the infection. C. albicans escapes the host defenses by rapidly switching between different phenotypic forms and by secreting carbohydrates that interfere with the complement cascade and promote inflammation.