HSBTE DMLT IVth Semester: Introduction to Mycology, Characteristics and classification of medically important fungi

1.1 INTRODUCTION TO MYCOLOGY

Mycology is the scientific study of fungi. Morphology, ecology, genetics, and medical significance of fungi are studied under mycology. Mycology is a multidisciplinary branch. It covers several fields such as botany, microbiology, ecology, genetics, and medicine.

Fungi are kingdoms separate from plants, animals, and bacteria. It constitutes a vast group of organisms ranging from microscopic molds to mushrooms. Mycologists are scientists who study fungi and investigate the ecological roles of fungi in nutrient cycling, decomposition, and symbiotic relationships with other organisms.

Medical mycoses are divided into four categories. These are cutaneous, subcutaneous, systemic, and opportunistic.

Importance of Mycology:

Mycology affects various aspects of human life. Fungi play important roles in various ecosystems and impact the lives of humans. Fungi contribute significantly to agriculture, industry, and medicine. The following are the importance of mycology in human life:

• 1. Food Production: Mycorrhizal fungi form symbiotic relationships with plant roots. They enhance nutrient uptake and promote plant growth. This association is crucial for the cultivation of many crops. This improves agricultural yields and ensures food security.

• 2. Biological Control: Certain fungi have biocontrol properties. They are natural agents to act against pests and pathogens in agriculture. This reduces the dependence on chemical pesticides. This promotes environmentally friendly farming practices.

• 3. Biotechnology and Industry: Fungi are utilized in various industrial processes. For example, species like Saccharomyces cerevisiae are essential in fermentation processes for brewing, baking, and bioethanol production. Additionally, fungi produce enzymes and organic acids used in the pharmaceutical and food industries

• 4. Biotechnology and Industry: Fungi are utilized in various industrial processes. For example, species like Saccharomyces cerevisiae are essential in fermentation processes for brewing, baking, and bioethanol production. Additionally, fungi produce enzymes and organic acids used in the pharmaceutical and food industries.

• 5. Medicine: Mycology plays a critical role in medicine, particularly in developing antibiotics like penicillin. Fungi also contribute to the production of immunosuppressive drugs and for cholesterol management.

• 6. Ecological Balance: Fungi are key nutrient cycling and decomposition players. They break down complex organic matter and return the nutrients to the soil. This facilitates the recycling of carbon and other elements. This ecological role is essential for maintaining healthy ecosystems.

• 7. Bioremediation: Fungi can degrade and detoxify various pollutants. Fungi treat the contaminated soil and water.

• 8. Research and Education: Mycological research contributes to the understanding of biodiversity, evolution, and ecological processes. It provides information about interconnectedness of living organisms. Mycology education also plays a vital role in training professionals in various scientific disciplines.

CHARACTERISTICS AND CLASSIFICATION OF MEDICALLY IMPORTANT FUNGI

Characteristics of medically important fungi:

Medically important fungi include a group of organisms that can cause infections in humans. Understanding the characteristics of these fungi helps accurate diagnosis, treatment, and prevention of fungal infections. The following are characteristics of medically important fungi:

• 1. Pathogenicity: Medically important fungi can cause infections in humans. These infections may be superficial infections of the skin and mucous membranes and systemic infections that affect internal organs.

• 2. Dimorphism: Some fungi exist in both yeast and mold forms. They switch between yeast and mold depending on environmental conditions. This is called dimorphism. Examples include Candida species and Histoplasma capsulatum.

• 3. Mode of Transmission: Fungal infections transmit through various routes, including inhalation of spores (as in the case of respiratory pathogens), direct contact with infected individuals or surfaces, or through the use of contaminated medical equipment.

• 4. Antigenic Variation: Certain medically important fungi undergo antigenic variation. The host's immune system does not sustain defense against this antigenic variation. This adaptability contributes to the resistance of fungal infections.

• 5. Thermotolerance: Many pathogenic fungi have thermotolerance. These fungi survive at the higher temperatures found within the human body. This characteristic of fungi causes infections in the host's tissues.

• 6. Biofilm Formation: Some pathogenic fungi form biofilms on the surfaces. This biofilm promotes fungi adherence and colonization. Biofilms provide protection against host immune responses and antimicrobial agents.

• 7. Cell Wall Composition: The composition of the fungal cell wall varies among species. These variations of knowledge help to develop antifungal drugs.

• 8. Mycotoxin Production: Certain fungi produce toxic metabolites known as mycotoxins. Mycotoxins contribute to the severity of some fungal infections and may cause additional health problems.

• 9. Host Immune Response: The ability of fungi to counteract host immune responses is a critical factor in establishing and progressing infections. Factors such as fungal capsule formation and the secretion of immunomodulatory molecules contribute to immune evasion.

• 10. Geographic Distribution: The presence of medically important fungi varies geographically. Certain fungal pathogens are more commonly found in specific regions. Understanding these distribution patterns is important for diagnosis and treatment planning.

• 11. Antifungal Resistance: Fungi can develop resistance to antifungal medications. This complicates the management of fungal infections.

Classification of Medically Important Fungi:

Fungi that cause infections in humans can be broadly classified into different groups. The following is a simplified classification based on the clinical presentation.

1. Cutaneous Mycoses:

Dermatophytoses: Dermatophytoses are superficial infections on skin, hair, and nails caused by fungi. Trichophyton, Microsporum, Epidermophyton are three dermatophytes to cause Dermatophytoses. Dermatophytoses spread through direct contact. Dermatophytoses are chronic infectious diseases favored by heat and humidity. Example: tinea infection (athlete’s foot, jock itch, etc). Symptoms of Dermatophytoses are pruritic papules, broken hair, and thick broken nails.

1. Subcutaneous Mycoses:

Fungi that grow in soil and vegetation infect subcutaneous tissues.

Sporothrix schenckii: Causes sporotrichosis, a subcutaneous infection often associated with plant material, It enters skin normally by a thorn. It causes local ulcers with nodules. It may be chronic.

Mycetoma Agents (e.g., Madurella, Actinomadura): These are soil organisms that enter the skin through wounds. It is a chronic infection involving the skin and deeper tissues. It develops pus that contains colored granules.

2. Systemic Mycoses:

Dimorphic fungi spores present in the soil enter the lungs through inhalation. Inside the lungs, dimorphic fungi spores develop into yeast. Most of the lung infections are asymptomatic and self-limited.

Histoplasma capsulatum: Causes histoplasmosis, often associated with bird or bat droppings,

Coccidioides immitis and C. posadasii: Cause coccidioidomycosis, endemic in arid regions.

Paracoccidioides brasiliensis: Causes paracoccidioidomycosis, prevalent in Central and South America,

a. Yeast

Candida spp.: Opportunistic pathogens causing candidiasis, often associated with immune-compromised individuals,

Cryptococcus neoformans and Cryptococcus gattii: Cause cryptococcosis, with a predilection for the respiratory and central nervous systems

1. Opportunistic Fungi

a. Pneumocystis jirovecii: Causes Pneumocystis pneumonia (PCP), primarily affecting immune-compromised individuals,

b. Aspergillus spp., Candida spp., Cryptococcus spp.: These fungi, under certain individuals with weakened immune systems.