Fungi

Fungi

• The Kingdom Fungi includes some of the most important organisms, both in terms of their ecological and economic roles

• Eukaryotic- contain membrane bound cell

• Are Heterotrophs- cannot manufacture their own food

• Most are saprotrophic (decompose dead matter). By breaking down dead organic material, they continue the cycle of nutrients through ecosystems.

• Many are parasitic (obtain nutrients from living organisms)

• Like plants, fungi have rigid cell walls and are therefore non-motile, a feature which separates them from animals

• Produce spores

Structures of Fungi

• Fungi occur in two basic growth forms• Yeast

• Unicellular fungi

• Reproduce by budding

• Mold (Filamentous fungi)

• Multicellular filamentous, “fluffy” colonies consisting of branching tubular structures called hyphae

• Collection of intertwined hyphae called mycelium

• Vegetative hyphae act like roots, penetrating the supporting medium and absorbing nutrients

• Aerial hyphae project above the surface of the mycelium and bear the reproductive structures of the mold (often spread through the air)

Draw and label these structures

Fungal Habitats

• Fungi can be found in soil, on plants, trees, and other vegetation, and on our skin, mucous membranes, and intestinal tracts• Some have distinctive ecologic and geographical niches.

Classification of Fungi

• A. Geographic grouping

• Classification by geographic distribution. Certain fungal diseases are considered endemic to particular areas

• Histoplasmosis - Central Mississippi Valley and Ohio Valley fever

• Coccidioidomycosis - San Joaquin Valley fever

• B. Epidemiologic grouping

• Concerned with how fungal disease is transmitted.

• Few are contagious - i.e. ringworm of the scalp. Some are inhaled, others must be directly introduced into deeper tissue such as by a puncture from a thorn.

• Most mycoses are dependent on the susceptibility of the individual host.

• C. Taxonomy grouping

• Scientific grouping according to morphologic and cultural characteristics; varies somewhat, depending on author.

Fungal Diseases

• Because fungi are more chemically and genetically similar to animals than other organisms, this makes fungal diseases very difficult to treat.

• Are often caused by fungi that are common in the environment

• Often difficult to diagnose because they may mimic bacterial infections. • Leads to inappropriate treatment with antibiotics, prolonged

illness, and delays in diagnosis & initiation of appropriate therapy

Fungal Diseases

• In 1991, an estimated 1.5 million fungi on the Earth• More recent estimates (2011)based on high-throughput

sequencing methods suggest that as many as 5.1 million fungal species exist

• ~300 are known to cause disease in humans

• humans are relatively resistant

• fungi are relatively nonpathogenic

• fungi are the most common plant pathogens

Fungi as infectious agents

• Mycosis- (Mycoses) disease process caused by fungi• spread generally from the environment to people (or animals) with

limited person-to-person spread.

• Skin and lungs are prominent entry site for many fungi

• Patients with impaired cell-mediated immunity (e.g. AIDS, organ transplant) at heightened risk for severe disease.

Fungi as infectious agents

• Types of fungal infections based on virulence and level of involvement of the disease

• Superficial: Outer skin layer - no immune response• caused mostly by yeasts (Dandruff)

• Cutenous: Epidermal layers - evoke immune response• Tinea (Ringworm, Athlete’s foot, jock itch) caused by

Dermatophytes

• Subcutenous: Chronic infection of subdermal tissues, may require surgical intervention

Fungi as infectious agents

• Types of fungal infections based on virulence and level of involvement of the disease• Systemic: Mostly originating in the lung

• Opportunistic: In immunocompromised conditions, (AIDS; altered mucosal flora due to antibiotics):

• mostly Candidiasis and Aspergillosis (often cause of epidemic death in birds)

Fungi as infectious agents

• Fungal pathogens can be classified in 2 categories• Primary (true) pathogens

• Have virulence factors that allow them to invade & grow in a healthy host

• Opportunistic pathogens

• Weak virulence; causes disease in only weakened or compromised hosts