Medical Mycology: Fungi and Human Health

Medical Importance of Fungi

• Relatively few fungal species infect humans, many produce antimicrobial medications, leading to a net positive impact on human health.
• Some fungal diseases are common, such as athlete's foot and jock itch.
• Life-threatening infections like cryptococcal meningitis are rare in healthy people, but more common and devastating in immunocompromised patients.
• Fungi cause human illnesses in three ways: Hypersensitivity reaction, infection (mycosis), and intoxication (ingestion of toxins).
• Fungal spores/conidia are everywhere, with high concentrations in the air, which can trigger allergies and asthma.
• Mycoses names often reflect the causative agent (e.g., candidiasis from Candida albicans) or the affected body part.
• Superficial mycoses affect the hair, skin, or nails, caused by dermatophytes.
• Systemic mycoses affect deep tissues, usually from inhaled spores.
• Some fungi produce toxins like aflatoxins (Aspergillus), which are carcinogenic and monitored by the FDA.
• The rye mold Claviceps purpurea (ergot) produces a hallucinogenic toxin, ergotamine, which is used to control uterine bleeding and relieve migraine headaches.
• Amanita species produce toxins that can cause fatal liver damage.

MicroAssessment 12.1 Summary

• Fungi have chitinous cell walls and secrete digestive enzymes to absorb nutrients.
• Fungi act as saprophytes, recycling carbon and other elements.
• They form symbiotic relationships (lichens, mycorrhizas).
• Fungi can be yeasts (single-celled) or molds (multicellular, with hyphae).
• Reproduction can be sexual (hyphae fusion) or asexual.
• While fungi cause plant diseases and food spoilage, they are also food sources and are used in food production.

Algae Overview

• Algae are simple photosynthetic eukaryotes.
• They differ from land plants by lacking a vascular system and having simpler reproductive structures.
• Most algae are aquatic; they can be microscopic or macroscopic.
• Algae do not directly infect humans, but some produce toxins that can be concentrated in other animals consumed by humans.
• Algae contain pigments for radiant energy absorption and are essential in aquatic environments for photosynthesis, converting CO₂ and H₂O to organic material (food) and O₂.

Types of Algae

• Algae are a diverse group of protists, characterized by their pigments.
• All contain chlorophyll a, with red and brown algae having additional pigments for different light wavelengths.

Structure of Algae

• Algae can be unicellular or multicellular.
• All contain chloroplasts with photosynthetic pigments and have rigid cell walls of cellulose.
• Red algae cell walls contain agar, and brown algae cell walls contain alginic acid.

Microscopic Algae

• Microscopic algae can be single-celled and free-floating.
• They may also exist in chains or filaments.
• They include diatoms and some green/red algae, dinoflagellates, and euglenids.
• They are adapted to aquatic environments with large absorptive surfaces for dilute nutrients.
• Some, like Volvox, form visible colonies.
• Diatoms incorporate silicon dioxide into their cell walls.
• Diatomaceous earth (diatom deposits) is used for filtering, abrasives, etc.
• Diatoms store oil for buoyancy and form crude oil/natural gas deposits over millions of years.

Macroscopic Algae

• Macroscopic algae include multicellular brown, green, and red algae.
• Some have a holdfast for anchoring, not for nutrient/water absorption.
• The stalk (stipe) has leaflike blades for photosynthesis; many have gas bladders for flotation.

Algal Habitats

• Algae are found in fresh/saltwater and moist soil.
• Aquatic algae are major O₂ producers and CO₂ users.
• They must live at water levels allowing light penetration; different pigments allow different levels.

Algal Reproduction

• Some algae reproduce asexually via fragmentation.
• Many alternate between haploid and diploid generations.

Medical Importance of Algae

• Algae do not directly cause disease but can do so indirectly.
• Algal blooms (rapid phytoplankton increase) occur in altered conditions.
• Upwelling and fertilizer runoff can cause blooms.
• Dinoflagellate blooms are red tides.
• Gonyaulax species produce neurotoxins such as saxitoxin and gonyautoxin.
• Shellfish accumulate these toxins, causing paralytic shellfish poisoning in humans.

The Biological and Economic Importance of Algae

• Algae are primary producers, fixing carbon through photosynthesis.
• Algae use is comparable to land flora.
• Phytoplankton forms the base of aquatic food chains.
• Algae stabilize soil and are used as fertilizer.
• Agar, alginic acid, and carrageenan are derived from algal cell walls.
• Diatomaceous earth comes from diatom glass walls.
• Carrageenan (from red algae) is a stabilizer/emulsifier in foods and is used in toothpaste, pharmaceuticals, ulcer therapy, and textile and paper industries.
• Agar (from red algae) is used as a solidifying agent in microbiological media and in the food industry for processed cheese, mayonnaise, puddings, and canned goods; it is also used as a drug carrier and in lotions.
• Alginic acid/alginates (from brown algae) are used in ice cream, cheeses, and bakery products.
• Industrial applications include paper manufacturing, fabric printing, and paint thickening.
• Alginate is used by dentists for teeth impressions.
• Laminaria japonica stipes are used for cervical dilatation.

Algae as Food

• Many algae species (mostly red and brown algae) are used as food in the Far East.
• Porphyra (red alga) is used to make dried sheets of "nori" in Japan.
• Algae are washed and spread on frames to dry into thin sheets.
• Nori is toasted and sprinkled in soup or rice and used to make a popular luncheon snack called sushi,.
• Porphyra cultivation has occurred since 1570.
• Other red algae, such as Chondrus, Acanthopeltis, Nemalion, and Eucheuma, are also consumed.