Pathogenic Yeasts – Fungi

by Vincent Racaniello, PhD

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    00:01 Some examples of yeasts that are pathogenic for humans.

    00:06 Now these are yeasts, the single cell organisms. Cryptococcus neoformans is a single cell growing organism in human, it causes a disease called Cryptococcosis. This yeast is present in the soil, it's present in decaying wood, in tree hollows, it is also present in the droppings of birds and the way you acquire this particular yeast infection, you inhale the organism.

    00:36 It goes into your lung where it can replicate. Now typically Cryptococcosis is not a disease that we find in healthy people. It usually occurs in immunocompromised people, for example people with AIDS often have Cryptococcosis, or if you have an organ transplant and your immune system is being immunosuppressed by drugs so that you don't reject the organ, if you inhale the cryptococcus neoformans, you can develop Cryptococcosis. And when the yeast does enter a human, it's inhaled as I said, it can get into the lungs, it can replicate in the lungs and cause a pneumonia-like illness, it can also travel to the brain and cause disease there and we call that meningitis. This is one disease that is not contagious from person-to-person, even though you might think that a fungal infection might be once it gets into a human, that's the end, it can't transfer to another human through the air.

    01:38 Now Cryptococcosis, in particular Cryptococcal Meningitis is a serious illness worldwide.

    01:44 You can see from this graph that there are cases in many different regions of the world, there are about a million new cases every year with 625,000 deaths and the majority of them as you can see, are in sub-Saharan Africa and that's probably because it's relatively dry and the spores of the organism travel more readily and they can be inhaled.

    02:08 Another pathogenic yeast is related to the cryptococcus we just talked about, it's called Cryptococcus gattii. This is again a yeast forming fungus, it's present in the soil and it's usually present in tropical and subtropical regions, it's become noteworthy lately because there have been a lot of cases in the US Pacific Northwest and in British Columbia shown in green on this map. Again you acquire the infection by inhaling the spores, they go into your lungs and there they cause disease. And again this fungus causes disease in immunosuppressed person such as people with AIDS and organ transplants, but they can also cause diseases in healthy people, and also those with lung disorders that don't happen to be immunosuppressed.

    03:05 If you smoke, you put yourself at risk for infection with this yeast. Again the yeast may cause a pneumonia-like illness by growing in the lungs, or it also can spread to the brain and cause meningitis. Just like cryptococcus neoformans, cryptococcus gattii does not travel from person-to-person.

    03:32 Another pathogenic yeast, again a yeast cell, the single cell type fungi, is Candida albicans, and this can cause a disease called candidiasis. On the left is a picture of Candida growing on an agar plate in the laboratory, and the picture on the right, emphasizes the point that this yeast is a normal inhabitant of humans. It grows on our skin and also in our mouth. It's only when we have some kind of imbalance in our body, does Candida overgrow and cause a disease, and that's often associated with various medical procedures. When you have an outgrowth of candida in the mouth, it's known as thrush or oropharyngeal candidiasis, and this is associated with redness and soreness, difficulty swallowing and you can often see a white coating on the tongue or on the mucosal membranes of the mouth. It can also cause infections in the genital, vaginal areas, this is called Genital/vaginal candidiasis, again these are normal inhabitants of these regions and when there is some imbalance, for some reason the candida overgrows and causes a problem.

    04:58 In addition to Candida causing disease in the mouth and the genital areas, it can also become invasive, it can get into the bloodstream and spread to different organs, it can spread through blood to the heart, brain, eyes and these are very serious infections. They don't typically occur unless the patient has been in a hospital. So for example, these kind of invasive candidiasis are associated with a stay in an intensive care unit, you are very sick, they're associated with being there, they're associated with individuals who have a central venous catheter inserted into the large vein in your chest to deliver for example antibiotics or other materials, long-term presence of that is associated with invasive candidiasis. They are also at risk in people with weak immune systems, again from immunosuppression, or infections that cause immunosuppression, or the use of broad-spectrum antibiotics, say to treat a bacterial infection, this will often disturb your normal microbial flora and allow the candida to overgrow.

    About the Lecture

    The lecture Pathogenic Yeasts – Fungi by Vincent Racaniello, PhD is from the course Microbiology: Introduction.

    Included Quiz Questions

    1. Dehydration from vomiting and diarrhea
    2. Oral erythema and tenderness
    3. Purulent genital discharge
    4. Disseminated infection, affecting particularly the heart, brain, and eyes
    5. A white coating on the tongue or the mucosal membranes of the mouth
    1. Inhalation
    2. Blood contamination
    3. Sexual transmission
    4. Contamination of conjunctival fluid
    5. In food
    1. Brain
    2. Heart
    3. Liver
    4. Spinal cord
    5. Skin
    1. Sub-Saharan Africa
    2. North America
    3. South America
    4. Europe
    5. North Africa
    1. North Africa
    2. North America
    3. South America
    4. Europe
    5. Sub-Sahara Africa

    Author of lecture Pathogenic Yeasts – Fungi

     Vincent Racaniello, PhD

    Vincent Racaniello, PhD

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