Linda Crampton is an experienced teacher with a first-class honors degree in biology. She writes about the scientific basis of disease.
A Useful Medicine for Yeast Infections
Nystatin is a very useful medication that often kills the Candida albicans yeast that infects humans. The yeast is generally harmless and lives permanently in our mouth, in our large intestine, on our skin, or in the vagina. Unfortunately, under certain conditions its population can grow dramatically, causing a disease called candidiasis. This disease ranges in severity from an uncomfortable and annoying condition to a deadly infection.
In most people, candidiasis is unpleasant but not dangerous. In people with weakened or suppressed immune systems, such as AIDS patients, organ transplant patients, and people receiving chemotherapy, candidiasis can be serious.
Nystatin is made by a bacterium called Streptomyces noursei. It was discovered in 1950 by scientists named Elizabeth Lee Hazen and Rachel Fuller Brown. The couple named the chemical after the New York State Health Department. They both worked for this department, though they lived in different cities.
The information in this article is provided for general interest. Anyone who suspects that they have a yeast infection should visit a doctor for a diagnosis and treatment recommendations.
Cells and Hyphae of Candida albicans
Yeasts are a type of fungus. Most yeasts consist of a single cell. They produce new individuals in the form of buds that separate from the parent cell. Other fungi have a different structure. Their body consists of branching, thread-like structures called hyphae. The tangle of hyphae that forms is called a mycelium.
Candida albicans exists as single, oval cells, like other yeasts. Its cells are surrounded by a wall made primarily of polysaccharides and proteins. The wall in turn surrounds the cell membrane. Unlike typical yeasts, a C. albicans cell sometimes produces filaments that resemble hyphae, as shown in the photo above. The filaments are present when Candida becomes invasive.
Candida albicans cells are shown below at a higher magnification. The cells have been stained and placed under a light microscope. The nucleus of each cell has absorbed a large quantity of the stain and is darker than its surroundings.
Invasive Candidiasis and Candidemia
The Candida albicans population in our bodies is normally kept at a low level by factors such as other microorganisms in the body, the environment in which the yeast is living, and our immune system. However, under certain conditions the population can increase and cause unpleasant symptoms.
In serious cases, the yeast can spread through the blood away from its initial site of colonization and cause infections in other organs, which is known as a systemic infection or invasive candidiasis. The presence of Candida in the blood is called candidemia.
Although Candida albicans is the most publicized species of the genus Candida in many areas, there are over twenty species in the genus that can infect humans.
Candida Infections and Fungal Biofilms
C. albicans causes "opportunistic" infections in humans. Most of the time, opportunistic organisms are not pathogens (ones that cause disease). They are able to increase in population size and cause health problems when there is a suitable change in their environment, however.
A troubling development with respect to Candida infections is the formation of yeast biofilms on implanted medical devices, such as catheters. A catheter is a thin tube inserted into the body for a medical reason, such as enabling the passage of fluid from a particular area. C. albicans exists in both yeast and hyphal forms in biofilms.
The microbes in a biofilm produce chemicals that help them stick to each other and to the surface on which they're living. They are much harder to kill than free-living microbes. Another problem is that biofilms can release microbes that produce infections in other areas of the body.
Investigating bacterial biofilms is a very active area of scientific research. Scientists are now paying increased attention to fungal biofilms as they realize how important they are.
Thrush or Oral Candidiasis
Candidiasis in the mouth is usually known as thrush or oral candidiasis. The yeast collections appear as white spots on the lining of the mouth or throat, on the gums or tonsils, inside the cheeks, or on the tongue.
The appearance of thrush generally means that there's been a change in the environment in the mouth or the body. Some conditions that promote the growth of the yeast population are listed below.
- Using inhaled corticosteroids to treat asthma without rinsing out the mouth afterwards
- Wearing dentures
- Taking antibiotics for another infection (probably because the antibiotics have killed the bacteria that help keep yeasts under control)
- Having a weakened immune system
- Having diabetes (probably due to an increased sugar level in the saliva)
- Being pregnant
- Being obese
Babies have an immature immune system and are susceptible to developing thrush, as the video below describes.
Treating Thrush in Newborn Babies
Candidiasis in Other Parts of the Body
In addition to appearing in the mouth, candidiasis may develop on the lips or skin, under a nail, in the gastrointestinal or reproductive tracts, around the anus, in the urinary bladder, or under a baby's diaper.
Although someone with candidiasis may need to take medications to deal with the yeast outbreak, if their immune system is healthy the yeasts are unlikely to travel beyond the external surfaces of the body or beyond the lining of the passageways connected to the external environment. In general, Candida only reaches the lungs in a person whose immune system isn't working efficiently.
Symptoms of a yeast infection depend on where it develops. They may include a thick, white discharge, redness, itching, and a burning sensation.
A Candida albicans Infection
The Discovery and Naming of Nystatin
The discovery of nystatin is an interesting story. The two women who discovered the chemical worked in different cities. Elizabeth Lee Hazen was a microbiologist based in New York City, while Rachel Fuller Brown was a chemist who lived in Albany. The women cooperated in the following way.
- Hazen collected soil samples, grew cultures of the microbes in each sample, and tested them for antifungal action against Candida albicans and another yeast named Cryptococcus neoformans.
- If she found activity she mailed the culture to Brown in a Mason jar.
- Brown extracted the active chemical from the culture and then mailed it to Hazen.
- Hazen then tested the extracted chemical on the two yeasts to see if it killed them. She also checked to see if the extract was toxic to animals.
One soil sample collected by Hazen came from the garden (or farm) of a friend named Walter Nourses. This sample contained a bacterium that produced a chemical that killed the yeasts yet was apparently safe for animals. Hazen named the bacterium Streptomyces noursei, using a species name to honor her friend, and called the active chemical fungicidin. Later the two women discovered that the name fungicidin was already used for another chemical, so they renamed their antifungal substance nystatin.
Value of Collaboration and Methodical Work
Without an efficient mail service and the patient, painstaking, and determined work of Elizabeth Hazen and Rachel Brown, nystatin might never have been discovered. The women lacked the relatively sophisticated lab equipment that we have today, as well as computer software, email, and video communication. Despite these apparent limitations, their methodical work enabled them to discover nystatin as well as other antimicrobial substances. Both women made other valuable contributions to science, but they are best known for their collaborative effort and their discovery of nystatin.
Nystatin Effects on Fungi
As in all fungi, the membrane around yeast cells contains a chemical called ergosterol. Nystatin targets this ergosterol. Ergosterol is a steroid molecule that helps the yeast membrane to maintain its correct structure. The membrane is a very important part of a cell. It determines which substances are able to enter and leave the cell.
Nystatin binds to ergosterol molecules and causes abnormal channels to appear in the membrane. These channels allow vital substances such as potassium ions to leave the yeast cells, resulting in their death.
Ergosterol is found in fungi but not in animals or humans. Therefore nystatin is able to kill fungal cells but is safe for our cells. There are newer antifungal medications available today, but nystatin is still widely used. It's one of a range of medicines that doctors can prescribe to treat a patient's fungal infection.
The word ergosterol is derived from ergot, a common name for the fungus Claviceps purpurea. This fungus infects rye and other grains. Ergosterol was first found in ergot.
Nystatin Effects on Humans
Nystatin is a prescription medication and must be used only after a doctor has been consulted. Other antifungal drugs are available. The doctor will prescribe one that is suitable for the patient’s condition.