Eukaryotes: Fungi, Helminths, and Arthropod Vectors

Flashcards covering fungi, molds, dimorphic yeasts, parasitic helminths (nematodes, cestodes, trematodes), and arthropod disease vectors from lecture chapters 7 and 8.

What are the primary general characteristics of fungi regarding nutrition, cellular structure, and cell walls?

Fungi are decomposers and heterotrophs that require an organic source of carbon, have chitin in their cell walls, digest food externally with enzymes to absorb nutrients, and can be single-celled or multicellular micro- or macroscopic organisms.

What are the optimal environmental pH and temperature ranges for mold growth?

Molds prefer a pH of $5\text{ to }6$ and a temperature of $20\text{ to }30\,^\circ\text{C}$.

What is the structural difference between a hypha and a mycelium in molds?

A single long strand is called a hypha, whereas combined strands together form a mycelium.

What is Rhizopus stolonifer commonly known as, and what is its appearance?

It is known as black bread mold, which decomposes bread for nutrients and consists of white filamentous hyphae with black sporulating structures.

What is the difference between sporangiospores and zygospores in Rhizopus stolonifer?

Sporangiospores are asexual replicating structures, whereas a zygospore is formed sexually from two different hyphae when nutrients or water are low to endure harsh environments.

What is the defining characteristic of the fungal group Deuteromycetes?

Deuteromycetes have no sexual reproduction.

Where is Aspergillus flavus typically found, and what pathology can its conidia cause when inhaled?

It is found on grains and peanuts; when inhaled, its conidia can grow in the lungs, causing farmer's lung or aspergillosis.

What is aflatoxin, and what serious medical condition is associated with high exposure?

Aflatoxin is a toxic metabolite ingested when moldy peanuts are eaten; high quantities can cause liver cancer.

What appearance do conidia give to Penicillium, and what are two practical uses of this genus?

Conidia give Penicillium a brush-like appearance; Penicillium notatum is used to produce penicillin, and other species are used in cheese production.

Why is Histoplasma capsulatum classified as a dimorphic fungus?

It grows as a mold at room temperature in the environment and as a yeast at body temperature within humans.

What environmental niche does the mold form of Histoplasma capsulatum inhabit, and what is the disease commonly called?

It is found in soil containing bird or bat droppings in caves, and the condition is referred to as Spelunker's disease (histoplasmosis).

How do Douglas fir saplings and mycorrhizal fungi mutually benefit each other?

The tree receives moisture and minerals trapped through mold decomposition, while the mold receives sugar produced by the tree via photosynthesis.

What two organisms comprise a lichen, and what does each contribute?

A lichen is composed of an algae or cyanobacterium and a mold; the producer (algae/cyanobacterium) provides sugar, while the mold traps and supplies water from decomposition.

What are the cellular characteristics and fermentation products of Saccharomyces cerevisiae?

It is a Gram-positive, unicellular yeast with oval budding cells that ferments sugar into alcohol and $CO_2$.

What normally keeps Candida albicans numbers low, and what clinical conditions result from its overgrowth?

The bacterium Lactobacillus keeps its numbers low; overgrowth caused by antibiotic use leads to thrush orally or vaginitis vaginally.

How does the germ tube test distinguish Candida albicans from Saccharomyces cerevisiae?

When grown in plasma broth, Candida albicans forms long extensions called germ tubes, whereas Saccharomyces cerevisiae forms buds.

Where is Cryptococcus neoformans found, and what disease can it cause in immunocompromised individuals?

It is an encapsulated yeast found in soil and pigeon droppings that can enter the bloodstream, cross the blood-brain barrier into cerebrospinal fluid, and cause meningoencephalitis.

What are the three main classifications of helminths based on appearance?

Nematodes (roundworms with cylindrical bodies and tapered ends), trematodes (flukes that are leaf-shaped and hermaphroditic), and cestodes (tapeworms with ribbon-like bodies and a scolex).

How is Enterobius vermicularis (pinworm) diagnosed in a laboratory?

By a scotch tape preparation placed on the perianal region to collect eggs that are flat on one side and curved on the other.

How does Necator americanus (hookworm) enter and migrate through the human body?

Larvae penetrate human feet from soil, enter the bloodstream, travel to the lungs, move up bronchial tubes and trachea, are swallowed, and mature in the small intestine.

How do humans contract Trichinella spiralis, and where do the larvae encyst in the body?

Humans contract it by eating undercooked pork containing larvae; after reproducing in the small intestine, larvae enter the blood and encyst in skeletal muscle.

What intermediate host transmits Diphyllobothrium latum to humans, and what are the symptoms?

Fish (consumed raw or undercooked); infection causes abdominal pain, anemia, and weight loss.

What are the definitive and intermediate hosts of the sheep liver fluke Fasciola hepatica?

Definitive hosts are sheep, cattle, and goats; the intermediate host is a freshwater snail.

What distinctive physical feature is found on a Schistosoma mansoni egg?

The egg is characterized by a prominent lateral spine.

What is the difference between a mechanical vector and a biological vector?

A mechanical vector carries microorganisms externally on its body (e.g., a fly), whereas a biological vector hosts part of the parasite's life cycle internally (e.g., a mosquito).

Which vectors transmit Plasmodium and Yersinia pestis?

The Anopheles mosquito transmits Plasmodium (malaria), and the flea transmits Yersinia pestis (plague or Black Death).

What disease is transmitted by the tsetse fly, and what organism causes it?

African sleeping sickness, caused by Trypanosoma brucei.

How does the reduviid bug transmit Trypanosoma cruzi to cause Chagas disease?

The bug defecates on the skin after biting, and the parasite is transmitted into the host from the infected feces.

What bacterium causes Lyme disease, what is its vector, and what is the characteristic initial sign?

It is caused by the spirochete Borrelia burgdorferi, transmitted by the Ixodes tick, and typically produces an initial non-itchy bull's-eye bite.