Fungi: Molds and Yeasts

Types of Fungi Yeast: unicellular Molds: multicellular

Molds The cells are filamentous structures called hyphae (singular = hypha). Hyphae are little tubes. Some have individual cells separated by crosswalls called septum. These are known as septate hyphae. Those without septums are called aseptate or non-septate hyphae. You can only see this under a microscope. The cell walls are made of polysaccharide (chitin or cellulose). When a mass of hyphae are visible, it is called mycelium.

Two kinds of hyphae in mycelium 1. Vegetative hyphae: these procure nutrients by secreting enzymes into the substrate (food source) which catabolize (break down) the nutrients, which are then sucked up through the hyphae. The vegetative hyphae also serve as an anchor on which they are growing. These hyphae are heterotrophs because they get energy by breaking down organic matter. Molds are the decomposers of the food chain, and that is also their ecological niche. Ecology is the study of the interrelationships of living things with each other and their environment. An environment contains both living and non-living things. These relationships should be balanced. Every living thing has a place. We can disturb the balance with our waste products. Fungi return organic matter to the earth by breaking it down with their vegetative hyphae.

Two kinds of hyphae in mycelium 2. Aerial hyphae: living things also need to reproduce; that is the role of the aerial hyphae. They reproduce by spore production. How are these spores different than bacterial spores? One hyphae produces thousands of spores, for reproduction. One bacterium produces one spore, for survival. Very few soil bacteria also make reproductive spores.

YEASTS The term “yeast” refers to just the morphology (single cell fungus, reproduces by asexual budding, may or may not have sexual cycle); “yeast” is not the taxonomy. Yeasts look like bacteria; they are smooth with no mycelium. They divide asexually by either binary fission (symmetrical) like bacteria, or by budding (asymmetrical). One yeast that produces alcohol is Saccharomyces, and is used in fermentation of beer and other alcoholic beverages.

Pathogenic Fungi and Their Diseases OPPORTUNISTIC MYCOSES Candida albicans (Candidiasis: yeast infection in women and thrush in children) Aspergillus (Aspergillosis) Cryptococcus neoformins (Cryptococcus) Pneumocystis (Pneumocystis pneumonia; most common pneumonia) CUTANEOUS MYCOSES (most common; fungus of the hair, skin, nails) Microsporum (scalp infections and ringworm) Epidermophyton (ringworm, jock itch, athlete’s foot) Trichophytum (ringworm, jock itch, athlete’s foot) SYSTEMIC MYCOSES (most serious; most often occurs in lungs) Coccidiodes immitis (Valley Fever) Histoplasma capsulatum (Histoplasmosis) Blastomyces dermatitidis (Blastomycosis)

Opportunistic pathogens Candida Aspergillus Cryptococcus Pneumocystis pneumonii Dermatophytes True Pathogens Histoplasma (true pathogen) Blastomyces (true pathogen)

Fungi Classification Kingdom Mycetae (Fungi) Division Amastigomycotina A. Subdivision Zygomycota B. Subdivision Ascomycotina C. Subdivision Basidiomycota D. Subdivision Deuteromycota

Fungi Classification Kingdom Mycetae (Fungi) Division Amastigomycotina A. Subdivision Zygomycota 1. Rhizopus stolonifer (zygote) 2. Rhizopus stolonifer (sporangiospore)

Fungi Classification Kingdom Mycetae (Fungi) Division Amastigomycotina A. Subdivision Zygomycota 1. Rhizopus stolonifer (black bread mold) Zygote (sexual spore) Hyphae

Fungi Classification Sporangiospores (asexual spores) Hyphae Kingdom Mycetae (Fungi) Division Amastigomycotina A. Subdivision Zygomycota 2. Rhizopus stolonifer (black bread mold) Sporangiospores (asexual spores) Hyphae Sporangium Sporangiophore Rhizoids Columnella

Hyphae Columnella Hyphae

Rhizopus Zygospore

A Young Rhizopus Zygospore

Mature Rhizopus Zygospore

Rhizopus Zygospores

Fungi Classification Kingdom Mycetae (Fungi) Division Amastigomycotina A. Subdivision Zygomycota B. Subdivision Ascomycotina C. Subdivision Basidiomycota D. Subdivision Deuteromycota

Fungi Classification Kingdom Mycetae (Fungi) Division Amastigomycotina B. Subdivision Ascomycotina 3. Penicillium notatum- ascospores (sexual spore) 4. Penicillium notatum- phialospore (asexual spore) 5. Morchella spp- ascospores (sexual spore) 6. Aspergillus niger - phialospore (asexual spore) 7. Saccaromyces cerevisiae -yeast- (asexual spore)

Fungi Classification Kingdom Mycetae (Fungi) Division Amastigomycotina B. Subdivision Ascomycotina 3. Penicillium notatum- ascospores (sexual spore) Cleistothecium (completely closed fruit body) Hyphae Ascus (sexual spore-bearing cell) Ascospore

Penicillium notatum sexual spores Cleistothecium (enclosed fruiting body) Ascus with ascospores

Fungi Classification Kingdom Mycetae (Fungi) Division Amastigomycotina B. Subdivision Ascomycotina 3. Penicillium notatum- phialospore (asexual spore) Phialospores Phialophore Phialide Metulae Septa Hyphae

Penicillium notatum asexual spores Phialospores Phialide Phialophore

PENICILLIUM (Latin for penicillus = “paint brush”) The branches off its phialophores are called metulae. This mold is famous for its use by Alexander Fleming in making penicillin, but it is also used to make aged cheeses like Brie, Blue cheese, and Roquefort. The white top layer of Brie cheese is where the vegetative hyphae are. The cheese is made with lactic acid bacteria (the curd is the cheese) and it is inoculated with Penicillium for flavor. The colony of Penicillium is green with a white ring.

Penicillium

Penicillium Penicillium

Fungi Classification Kingdom Mycetae (Fungi) Division Amastigomycotina B. Subdivision Ascomycotina 5. Morchella spp- ascospores (sexual spore) Hyphae Ascus Ascospore

Morchella Edible mushrooms with honeycomb appearance. Mushroom hunters refer to them by their color (e.g., gray, yellow, black morels) Black Morel Yellow Morel

Fungi Classification Kingdom Mycetae (Fungi) Division Amastigomycotina B. Subdivision Ascomycotina 6. Aspergillus niger - phialospore (asexual spore; a type of conidiospore) Phialospores Phialophore Hyphae Vesicle Phialide

Aspergillus

Aspergillus Aspergillus gets its name from “aspergillum”, the name of the item a Priest uses to bless with Holy water. Aspergillus is a very common fungi, pervasive (found everywhere). There are more than 600 species. Most are saprobic (non-pathogenic) and live off dead matter. In a young fruiting body, the “handle” of the conidia is called the conidiophore. The bulb at the top is called the vesicle. The philiae radiate out from the vesicle, and the spores form chains in the philiae. The older fruiting bodies look like a toilet brush because they are covered with spores at all angles.

Aspergillum

Aspergillus Some Aspergillus fungi can ferment. That’s where we get citric acid for soft drinks and also soy sauce. One pathogenic species is called Aspergillus flavus. It produces a toxin called aflatoxin (a mycotoxin) which is carcinogenic, especially in the liver (liver cancer). This species is fond of grains (corn, wheat), and peanuts, and jelly. Therefore, a peanut butter and jelly sandwich is a triple whammy for aflatoxin. It dissolves in the jelly, so scooping it off the top surface of the jar will not do any good. To prevent aflatoxin, only buy peanut butter and jelly in the size jars you use up in a week, keep them refrigerated (the bread, too), and use a clean knife each time. Don’t leave the lid off for long, because that’s when it gets in. Another disease Aspergillus causes is aspirgillosis, a lung disease.

Aspergillosis Aspergillosis: can occur anywhere in the body, but is most common in the lungs. Some people just have allergies to this mold. X-ray of aspergillosis shows aspergilloma (“fungus balls”) which are mycelium and white blood cells. Although opportunistic diseases are usually seen in immunocompromised people, healthy people who are overexposed can also get sick. Since this mold loves grains, farmers are especially at risk.

Aspergillus

Aspergillus Aspergillus

Aspergillus

Aspergillosis

Aspergillosis Aspergilloma (Fungus balls)

Fungi Classification Kingdom Mycetae (Fungi) Division Amastigomycotina B. Subdivision Ascomycotina 7. Saccaromyces cerevisiae -yeast- (asexual spore) Parent cell Blastospore

Saccaromyces (“sugar mold”) cerevisiae (“beer”)

Saccharomyces cerevisiae

Fungi Classification Kingdom Mycetae (Fungi) Division Amastigomycotina A. Subdivision Zygomycota B. Subdivision Ascomycotina C. Subdivision Basidiomycota D. Subdivision Deuteromycota

Fungi Classification Kingdom Mycetae (Fungi) Division Amastigomycotina C. Subdivision Basidiomycota Club fungi; mushrooms, rusts, smuts. 8. Coprinus spp. Basidium Basidiospores Basidiophore Hymenium (cup area where spores develop)

Coprinus (mushroom)

Coprinus with Basidiospores

Coprinus with Basidiospores

Coprinus

MYCOTOXINS Basidiomycota are mushrooms which are either edible or deadly. The species agaricus is the edible “Button mushroom” in stores. The species amanita is deadly and produces a mycotoxin called phaloidin (damages liver). The species psilocibe (called “magic mushrooms”) produces a mycotoxin called psilocybin, which is a hallucinogen like LSD.

Fungi Classification Kingdom Mycetae (Fungi) Division Amastigomycotina A. Subdivision Zygomycota B. Subdivision Ascomycotina C. Subdivision Basidiomycota D. Subdivision Deuteromycota

Fungi Classification Kingdom Mycetae (Fungi) Division Amastigomycotina D. Subdivision Deuteromycota Fungi imperfecti Species of fungi that are asexually reproducing members of the fungal phyla Ascomycota and Basidiomycota.

Other Pathological Fungi The following are other important fungi because of the diseases they cause. We do not have slides of these, but you are required to know them; they are on the exam. Many pathological fungi are molds (multicellular) in the environment, but change to a yeast form (unicellular) once they have invaded the human body. This is called thermodimorphism.

Blastomyces dermatitidis DISEASE: Blastomycosis Caused by inhalation of conidia; only a few spores are needed to establish infection. Spores germinate to yeast and are engulfed by macrophages. This is followed by inflammation and granuloma formation. Most cases are asymptomatic or mild. Symptoms may include cough, chest pain, hoarseness, fever. Dissemination in severe cases can overwhelm the patient. Organisms may cause granulomas in the lungs that have been mistaken for malignancies. They tend to spread to the bones (arthritis), brain (headache-coma), and skin (ulcerating nodules from subcutaneous tissue).

Blastomyces dermatitidis

Histoplasma capsulatum This organism is found in soil that is rich in nitrogen, especially caves with bat droppings (guano). Such caves are moist, rich in nitrogen, and have dead organic material there, which are ideal conditions for molds. Spelunkers are people who explore caves, usually on their hands and knees. Their nose is close to the floor, so they inhale the conidia spores. Hunting dogs get it the same way. When you hear the word “cave”, think of Histoplasma.

Histoplasma capsulatum DISEASE: Histoplasmosis Microconida are inhaled. The disease starts with flu-like symptoms and a cough. In the immunocompromised (those with emphysema, bronchitis, or HIV), the organisms are ingested by macrophages but not killed, and are disseminated (spread throughout the body). These patients develop fever, weight loss and night sweats, and the condition becomes chronic and relapsing. This form is called Chronic Pulmonary Histoplasmosis. X-rays show lesions that are similar to TB, but the medicines are different, so making the differential diagnosis (DDx) is important.

Histoplasmosis There is a skin test for histoplasmosis, similar to the one for TB. You can also do a KOH wet mount on a skin lesion; a budding yeast is diagnostic. Treatment is Amphotericin B or Fluconazole. These just treat the disease, but it won’t cure it.

Histoplasmosis Histoplasmosis is the cause of the "Mummy's curse" after unearthing King Tut's tomb in the 1920's. Approximately 80% of the population in central states are skin positive for exposure to the organism. Approximately 500,000 cases each year in the USA.

Histoplasma capsulatum

Histoplasmosis

Histoplasmosis

Histoplasmosis

Histoplasmosis

Coccidioides immitis DISEASE: San Joaquin Valley Fever Also called Valley Fever, or coccidioidomycosis. Approximately 100,000 cases per year in USA. Cases occurred in So. California following the earthquakes in San Fernando in the late 1980's. It is a recurring disease with treatment but no cure. Treatment is Amphotericin B or Fluconazole. Note that there are only a few drugs for the mycoses, while there are many antibacterial medicines.

Coccidioides immitis Arthrospores are inhaled and thermodimorphism occurs (changes shape with body heat), and the sporangia form into spherules in the lungs. The spherules mature and release the spores which disseminate and develop into more spherules. Many cases are asymptomatic; others may have flu-like symptoms. Most will recover without incident and then have lasting immunity. Individuals with impaired cell-mediated immunity (T-cell dysfunction) will progress into chronic symptoms. In those cases, nodules form in other tissues, especially the bone marrow, brain and epidermis. Prevention: oiling roads, wearing masks, planting vegetation to reduce aerosols.

Valley Fever The people are not contagious because the infectious stage in the environmental phase. This organism differs from Histoplasmosis and Blastomyces in that it requires long periods of dry (arid) weather, and then a heavy rain. That makes it endemic to west Texas, Mexico, Baja, South America, Southern California, Arizona, and New Mexico. The blood of everyone who lives in the San Joaquin Valley tests positive for the organism, but they don’t usually get the disease. That’s because you need to be exposed to a large amount to get sick; therefore farmers are at risk. Caesar Chavez fought for the rights of immigrant farm workers, who were given short tools to weed the farms, so their noses were close to the ground and they inhaled the spores often. They also were not paid well and had poor nutrition, so they would get the disease.

San Joaquin Valley Fever

Coccidioides immitis arthrospores

San Joaquin Valley Fever

Cryptococcus neoformans DISEASE: Cryptococcosis The organism is an encapsulated yeast cell; a normal soil inhabitant. Lives in soil rich in nitrogen, especially bird droppings. It is most often associated with pigeon droppings, so it is common in urban areas (cities). It is not as common in rural (country) areas. People do not get sick unless their immune system is not healthy.

Cryptococcosis Spores are inhaled, and the disease starts out as a primary pulmonary infection with flu-like symptoms of cough, congestion, fever. Nodular lesions may develop in the lungs. Most people recover easily, but may have scars called cryptococcomas. In the immunocompromised, the disease disseminates (spreads) to the blood and then to the CNS (central nervous system). It causes neurological damage in those who survive. The Blood-Brain Barrier (BBB) does not allow compounds of large molecular weight to cross into the brain, so most drugs cannot treat CNS infections. Treatment is either Amphotericin B (injected or IV), which is potent, but side effects include kidney damage, or Fluconazole (or other “azole” medicines) which is oral (pill form).

Cryptococcosis This disease can cause meningitis (headache, fever, stiff neck), but so do many other diseases, including bacteria and viruses. The meds for each disease are different, so it is important to make the correct differential diagnosis (DDx: to differentiate this organism from others). The azole medicines affect the sterols in the plasma membrane, so they work on fungi, but most bacteria do not have sterols.   A sample of CSF (cerebrospinal fluid) is taken from the patient and cultured and stained with India ink. Seeing a budding yeast with a huge capsule around it is diagnostic. The capsules serve to resist phagocytosis (being eaten) by white blood cells.

Cryptococcosis

Cryptococcus Filobasidella (Cryptococcus) neoformans

Cryptococcosis

Cryptococcosis, disseminated

Pneumocystis carinii DISEASE: Pneumocytosis, or pneumocystis pneumonia (PCP). This disease is associated with infections in immunocompromised persons, especially HIV. It is a normal inhabitant of soil. The organism is inhaled and multiplies extracellularly. This results in the alveolar spaces filled with foamy material. The person eventually has difficulty with obtaining enough oxygen and the become hypoxemic. Symptoms include fever, dry cough, tachypnea (fast breathing) and cyanosis (blue skin).

Pneumocystic carinii

Pneumocystis pneumonia

Candida albicans This is a yeast which is a common normal inhabitant of the human skin and mucus membranes. 30% females have Candida in the vaginal tract and 50% of humans are colonized in their GI tracts. Endogenous flora compete with each other and should remain balanced. If one organism dies off (such as after antibacterial medicines) one other organism (like Candida) can take over and cause disease. Most common disease patterns include thrush (oral candidiasis) and vaginal yeast infections.

Candidiasis DISEASE: Candidiasis The oral form of this disease is called thrush. It can occur in newborns after passing through a birth canal, since babies don’t have a fully formed immune system until after they are a year old. Thrush can also occur in diabetics, elderly, and AID patients. When it occurs in the esophagus, it makes it hard to swallow. When the disease is in the vagina, it is called vulvovaginitis (affects 5% of women right now). It can also occur in wet areas of the skin and is common among dishwashers. This form is called Cutaneous Candidiasis, and can be mistaken for a bacterial “jock itch” or diaper rash. Although it looks like a dermatophyte infection, those creams won’t work here.

Candida albicans

Candida

Candidiasis: thrush

Thrush in an adult

Cutaneous Candidiasis

II. Dermatophytes There are greater than 30 species that infect humans but the most common six follow. A. Epidermophyton floccasum B. Microsporum canis C. Microsporum gypseum D. Trichophyton rubrum E. Trichophyton mentagrophytes F. Trichophyton tonsurans

Epidermophyton floccasum Infects groin, body, feet, occasionally nails, but does not infect hair.

Microsporum canis Causes tinea capitis in humans, and ringworm in pets.

Microsporum gypseum Causes tinea capitis, tinea corpus, ringworm.  It does not fluoresce under Wood's ultra-violet light.

Trichophyton rubrum This is the most common cause of athlete's foot, jock itch and ringworm. Causes the dry, red, thick-skinned type of athlete’s foot.

Trichophyton mentagrophytes Causes athlete's foot, ringworm, jock itch, and infections of the nail, beard, skin and scalp. Causes the wet, macerated type of athlete’s foot between the toes.

Trichophyton tonsurans This is the most common cause of tinea capitis (scalp infection).

Dermatophyte Infections Dermatophytes are fungi that live on keratin (found in skin, hair, and nails). Dermatophyte infections are the most common fungal infections in humans. The diseases they cause are known as “tinnea”. When a person has tinnea, doctors don’t know which dermatophyte is the causative agent unless they culture it, so they name the disease according to its location. Fungi like moisture, and feet are in a dark, moist environment, so infection is common there. Athlete’s foot is known as tinnea pedis. You get it by just walking barefoot, exposing the skin to the air where spores are. If there is a slight scratch in the skin, the fungi can get in. They form itchy vesicles. When scratched, the fungus spreads. Treatment is topical creams. When dermatophytes infect the nails it is called onychomycosis. The nails get thick, chalky, discolored. Topical creams don’t penetrate the nails. Oral medicines like griseofulvin kill the fungus but are also toxic to the liver. Onychomycosis is common with age.  Ringworm: these skin lesions are circular, so they look like a worm. Ringworm can also occur in the scalp, usually in children. The hyphae are fluorescent, so you can use a Wood’s Lamp, which shines with ultraviolet light, and see the hyphae glow.  When dermatophytes cause a skin rash, they can be diagnosed by scraping a bit of the skin onto a slide, and adding KOH, which dissolves the skin cells and leaves the hyphae. The hyphae, when observed under the microscope, are diagnostic for dermatophytes.

Dermatophyte Infections Tinea capitis - scalp Tinea corporis - body Tinea barbae - beard Tinea cruris - groin (Jock itch) Tinea pedis - feet (athlete’s foot) Tinea unguium – nails (onychomycosis) Ringworm: term for any fungus that forms a ring shape in the skin Diagnosis of Dermatophytes 1. Yellow fluorescence with Wood's lamp 2. KOH wet mount 3. Culture Oral Medicines if topicals don’t work 1. griseofulvin 2. fluconazole

Tinea capitis - scalp

Tinea corporis - body

Tinea barbae - beard

Tinea cruris - groin

Tinea pedis - feet

Tinea unguium – nails

Dermatophytes: Ringworm