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.
© 2010, J.Graf. Site made by Noah Strickland, for comments please contact Joerg.Graf@uconn.edu