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Over 1500 different yeast species have currently been identified and it is believed that they emerged on earth millions of years ago. They are single celled organisms and belong to the fungus kingdom, which are decomposers. Although they are single celled organisms some of them produce hyphae like roots on a tree, which gives them multi-cellular characteristics.
Their preferred food source is carbohydrates from glucose and fructose, which are single celled saccharides. Some species also have the ability to consume disaccharides such as maltose and sucrose. They prefer oxygen for growth but some species can grow without it on a limited basis but oxygen will be required at some point for long term survival.
Although roughly 150 species can be pathogenic to humans, it is known that approximately 65% of Candida species are unable to grow at a temperature of 37 °C, 98.6 F, which precludes these species from being successful pathogens or indeed commensals of humans.
Most reproduce by budding or basically by splitting a cell in two to
produce a new, although immediately smaller, cell. That cell will
continue to grow to maturity before splitting off from the original
Generally, most yeast species are opportunistic human pathogens and under the right circumstances, all have the ability to kill a human being. They have become the fourth leading cause of hospital infections and are every bit as bad as bacterial sepsis, which often requires iv antibiotics to save the persons life.
I know of two cases where candida yeast got into the persons blood stream. One you can read about here, the other died from candida caused kidney failure.
Here we take a look at the most common yeast species that can infect the human body. Each short paragraph will identify the species and will include a link where you can click over and review what it is, some of the symptoms it can cause, what parts of the body it typically infects, and how you can treat it.
It should be noted, that all of these candida yeast species below build biofilms and you must remove these biofilms in order to be successful in treating it. They also have the same basic cell structure. Please see this page for more information on biofilms and the structure of yeast.
Because this page is a work in progress, more species will be added over time for you to review.
Candida albicans is a hyphae, pseudohyphae and bud producing yeast species that accounts for 54% of infections in the US and 66% worldwide. It has been suggested that 100% of people have this yeast species in their intestine although a normal level is undetectable using modern medical, stool test, detection methods.
Infected individuals can be infected with more than one biotype of candida albicans at the same time. 90% of the time strains isolated from the vagina, urethra and anus are the same species. 25% of the time infections with oral involvement are a different biotype than what is found in the intestine.
Candida glabrata does not produce hyphae but does produce spores and accounts for 19% of infections in the US and 11% worldwide. C. glabrata ferments and assimilates only glucose and trehalose, which is artificially produced from corn starch and used as a food additive.
Candida parapsilosis does not form true hyphae and exists in either a yeast phase or a pseudohyphal form. It accounts for 11% of infections in the US and 6% worldwide. C. parapsilosis is often considered less virulent than C. albicans but it is the Candida species with the largest increase in incidence since 1990.
Candida tropicalis forms pseudohyphae with buds and accounts for 11% of infections in the US and 6% worldwide. It is considered to be more virulent than candida albicans because of its increased potential for tissue invasiveness.
Candida krusei is a budding yeast and accounts for 2% of infections in the US and 2% worldwide. It has natural resistance to fluconazole and has a higher mortality rate than candida albicans.
Candida guilliermondii is an emerging pathogen that accounts for 1.4% of infections worldwide. It has resistance to fluconazole but does respond well to voriconazole.
Candida rugosa accounts for about .6% of infections worldwide and seems to be the more prevalent in Latin America and India. It is resistant to fluconazole but does respond well to voriconazole.
Candida lusitaniae forms pseudohyphae upon which chains of blastoconidia(buds), develop and is becoming a more prevalent emerging yeast pathogen.
Aspergillus fumigatus is actually a fungi found in the soil and organic debris all over the world. It produces hyphae and conida and commonly infects the sinus and lungs of immuno-compromised humans. It requires phosphatase calcineurin for growth, a compound that is required by humans to maintain a healthy immune system.
Cryptococcus neoformans is also found in the environment and is a basidiomycete yeast, they bear their spores on a basidium, and include the smuts, rust, mushrooms, and puffballs. It has the ability to survive inside human macrophages and when host defenses deteriorate, it infects its host.
Malassezia also infects the skin and most commonly causes dandruff and seborrhoric dermatitis. It prefers the fat from your sebaceous glands for food so it is mostly found on the upper part of the human body which is generally more oily than the lower half. Ketoconazole containing shampoos work well to get it under control.
Rhodotorula mucilaginosa is a unicellular pigmented yeast that has a distinctive orange/red color when grown on Sabouraud's Dextrose Agar in a lab. It has been found in the soil, water, milk, peanuts, apple cider, cherries, fresh fruits, fruit juice, cheese, sausages, edible molluscs, crustaceans, and it has been suggested that contaminated foods could lead to infection. I see this species on stool test results from time to time.
Saccharomyces cerevisiae is a yeast species that is commonly used to make wine, beer, and to bake with. It does not produce hyphae or pseudohyphae but reproduces by budding. It can and does infect humans with antibodies against it being found in 60 to 70% of people with Crohn's disease, 10–15% of patients with ulcerative colitis verses 8% in healthy people.
Tinea are dermatophytes and can infect the skin anywhere on the body. They also can infect the nails and are responsible for most cases of toenail fungus. This article goes into detail on all these various types of infections.
Trichosporon is an asexual yeast species that is commonly found on the skin of humans and other animals. An over growth of trichosporon yeasts in the hair can lead to an unpleasant but non-serious condition known as white piedra. These infections can be treated with azole drugs and azole antifungal shampoo with very good success.
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Article written by Dan and edited for accuracy by Dr. Taylor
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