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Candidiasis – Opportunistic Infections

by Vincent Racaniello, PhD
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    00:01 The first opportunistic infection we'll consider is candidiasis. Now opportunistic signifies that in most people, these fungi do not cause disease, it's only when there's an opportunity, such as immunosuppression, do they cause problems. And candidiasis may be caused by three different species of candida; Candida albicans, Candida glabrata and Candida parapsiloses. And these pictures of candida show the typical fluffy white appearance of the colonies on an agar plate, that's the picture on the left and on the right is in the microscope, you can see the single cells of Candida. So this can assume a yeast configuration, it can also assume a mycelial configuration. Candida species are normal inhabitants of our skin and our mucosal surfaces, such as our mouth and the genital tract. So here's a case where everybody has these bacteria, excuse me, everybody has these fungi, but in only certain situations do they cause disease. So, when is candidiasis a problem? Those individuals at risk for this disease include: the immunosuppressed, if you're having an organ transplant and you need to have drugs to reduce the risk of rejection of the organ, patients in intensive care units, the use of broad-spectrum antibiotics that can alter the normal microbial flora and allow certain species to overgrow, people who have kidney failure and they require dialysis and needles need to be inserted into these individuals repeatedly, that can introduce the candida below the surface of the skin, which is where it normally inhabits. Central intravenous catheters, people with catheters for example, people with catheters in the main veins of the chest who need them for various reasons, these can introduce bacteria and Candida into that region. Those people receiving nutrition by means other than by the mouth, that's what parenteral means, so for example by intravenous feeding, or people with AIDS, because they are immunosuppressed. These fungi don't cause infection unless the normal flora is disrupted.

    02:29 So all the conditions we just talked about may lead to the disruption of the normal flora or introduction of candida, where it shouldn't be, so you may have a skin maceration which inadvertently pushes the Candida species where they shouldn't be and that can cause infection.

    02:48 So alteration of the flora by medical procedures, or disruption of the skin. These procedures cause the Candida to get into the bloodstream. So for example chemotherapeutic agents that destroy the mucosal gut barrier, these are normal inhabitants of the gut as well.

    03:04 If you're taking drugs that change that barrier, many anticancer drugs do that, can allow the Candida to come in and as I said before central venous catheters that deliver medications to the major veins and arteries of the body, these are at risk for introducing microorganisms, because they are not only inside the body, they come outside as well and the organisms can get in that way.

    03:31 Normally the Candida species on our mucosal surfaces are held in check by our immune response and specifically for Candida this is T cell-mediated immunity. So the Candida is living in places in our body, we presumably derive some benefit from that and the balance of the two is mediated by T cells. When that's disrupted, then the Candida can overgrow. AIDS patients in particular are at risk because they have reduction in their T cell efficacy as a result of virus infection. So they frequently develop oral pharyngeal and vaginal candidiasis, it's a very typical outcome of AIDS infections, that among the other opportunistic infections that these individuals acquire, one of them is candidiasis, which is very obvious because it presents, at least partially in the mouth, as a white coating as the fungi grows on the tongue.

    04:36 Neutrophils are the main host defense against invasion and dissemination. These cells prevent the candida from normally invading beyond the mucosal and skin layers where they normally inhabit, but again, any kind of procedure that disturbs the immune balance and particularly neutrophils, will allow Candida to get inside of us. There are a number of people who are what we call neutropenic, they have low levels of neutrophil, as a variety of reasons.

    05:08 It could be infection or drug treatment. In these individuals the candida is not properly controlled and it frequently spreads via the blood to other organs, such as the eyes, the kidneys, the heart, brain, the liver, the spleen and there the Candida can multiply and cause extensive problems. Candidiasis manifests itself visually by a white coating of thick cells on the mucosal surfaces of the mouth, of the reproductive organs and this is often called thrush. And this is very common in babies who are born vaginally, by a vaginal delivery. Females have Candida in the vaginal tract as a normal flora, and some women have higher levels than others, some babies may be slightly more immunosuppressed than others, but it's a very common occurrence within a few days of birth for babies to develop a white coating on their tongue called thrush, which then can be treated without any further effects.

    06:09 There is another form of candidiasis called Intertriginous candidiasis. This is when the fungus grows in the warm and moist areas of the skin, such as the groin, so babies often get a diaper rash and it can involve Candida. This is because, of course, the diaper is holding the moisture in, especially modern diapers that are very sealed against fluid leakage, they can keep in the moisture and the heat, the Candida can grow there. These individuals are not necessarily immunosuppressed, although babies’ immune systems are not as good as older individuals’ immune system. And there's also Candida which may grow underneath breast tissue. This is actually a good reason to wear a bra, because if you have breasts that press against the chest, there will be a region of skin under them that is dark and moist and if you have any immune issue whatsoever, Candida can grow under there. So these are called intertriginous candidiasis.

    07:11 When Candida goes beyond the mucosal and skin surfaces, we call it a disseminated infection, this can then bring the yeast to many other organs. It can infect the brain, leading to meningitis. It can infect the eye, in particular the retina and the membranes just on top of the retina, this is called Chorioretinitis. It can cause abscesses in the spleen and in the liver, Hepatosplenic abscesses. It may involve the vertebral column and called vertebral osteomyelitis. And finally it can cause heart infections, especially if you have an artificial valve, a prosthetic valve, it can cause endocarditis at that site. So the yeast can go from its normal site on mucosal surfaces in the skin to many other regions when we have problems.


    About the Lecture

    The lecture Candidiasis – Opportunistic Infections by Vincent Racaniello, PhD is from the course Fungi.


    Author of lecture Candidiasis – Opportunistic Infections

     Vincent Racaniello, PhD

    Vincent Racaniello, PhD


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