Mycology

Growth Forms and Reproduction

Growth forms

• Multicellular Multicellular Cell Types: Eukaryotic versus Prokaryotic forms include molds and mushrooms:
  • Mostly composed of thread-like hyphae:
    • Septated: Cell walls subdivide the hyphae.
    • Coenocytic: Hyphae lack cell walls.
  • Familiar “mushrooms” are reproductive organs (thallus) of fungi.
  • Tubular network systems in which hyphae form branching nets (mycelium)
• Unicellular Unicellular Cell Types: Eukaryotic versus Prokaryotic forms include yeasts:
  • Yeasts do not have hyphae or mycelium.
  • Some species form pseudo-multicellular structures (budding yeasts).
• Dimorphic fungi:
  • Can exist as unicellular Unicellular Cell Types: Eukaryotic versus Prokaryotic or multicellular Multicellular Cell Types: Eukaryotic versus Prokaryotic forms
  • Environmental factors (temperature, humidity, presence of nutrients) can trigger Trigger The type of signal that initiates the inspiratory phase by the ventilator Invasive Mechanical Ventilation changes.

Structure

• Fungal cells have characteristics similar to both plant and animal cells:
  • Characteristics that are common with animal cells:
    • Presence of a membrane-bound nucleus Nucleus Within a eukaryotic cell, a membrane-limited body which contains chromosomes and one or more nucleoli (cell nucleolus). The nuclear membrane consists of a double unit-type membrane which is perforated by a number of pores; the outermost membrane is continuous with the endoplasmic reticulum. A cell may contain more than one nucleus. The Cell: Organelles
    • Organelles Organelles A cell is a complex unit that performs several complex functions. An organelle is a specialized subunit within a cell that fulfills a specific role or function. Organelles are enclosed within their own lipid bilayers or are unbound by membranes. The Cell: Organelles such as mitochondria Mitochondria Semiautonomous, self-reproducing organelles that occur in the cytoplasm of all cells of most, but not all, eukaryotes. Each mitochondrion is surrounded by a double limiting membrane. The inner membrane is highly invaginated, and its projections are called cristae. Mitochondria are the sites of the reactions of oxidative phosphorylation, which result in the formation of ATP. They contain distinctive ribosomes, transfer RNAs; amino Acyl tRNA synthetases; and elongation and termination factors. Mitochondria depend upon genes within the nucleus of the cells in which they reside for many essential messenger RNAs. Mitochondria are believed to have arisen from aerobic bacteria that established a symbiotic relationship with primitive protoeukaryotes. The Cell: Organelles
    • Lack of chloroplasts
  • Characteristics that are common with plant cells:
    • Presence of a cell wall Cell wall The outermost layer of a cell in most plants; bacteria; fungi; and algae. The cell wall is usually a rigid structure that lies external to the cell membrane, and provides a protective barrier against physical or chemical agents. Cell Types: Eukaryotic versus Prokaryotic
    • Contain vacuoles
• Fungi have unique properties that distinguish them from animals Animals Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, animalia was one of the kingdoms. Under the modern three domain model, animalia represents one of the many groups in the domain eukaryota. Cell Types: Eukaryotic versus Prokaryotic and plants Plants Cell Types: Eukaryotic versus Prokaryotic:
  • Cell walls contain chitin Chitin A linear polysaccharide of beta-1->4 linked units of acetylglucosamine. It is the second most abundant biopolymer on earth, found especially in insects and fungi. When deacetylated it is called chitosan. Echinocandins, unlike plant cell walls that contain cellulose.
  • Cell membranes contain ergosterol Ergosterol A steroid occurring in fungi. Irradiation with ultraviolet rays results in formation of ergocalciferol (vitamin d2). Azoles, unlike animal cell membranes that contain cholesterol Cholesterol The principal sterol of all higher animals, distributed in body tissues, especially the brain and spinal cord, and in animal fats and oils. Cholesterol Metabolism.

Reproduction

Reproduction is either sexual or asexual.

• Types of asexual reproduction: 
  • Binary fission Binary fission Cell Types: Eukaryotic versus Prokaryotic
  • Breakdown of hyphae, dispersal, and regrowth
  • Budding (yeasts)
  • Formation of conidia (containing asexual mitotic spores Spores The reproductive elements of lower organisms, such as bacteria; fungi; and cryptogamic plants. Anthrax)
• Sexual reproduction:
  • Merging of 2 haploid Haploid The chromosomal constitution of cells, in which each type of chromosome is represented once. Symbol: n. Basic Terms of Genetics cells:
    • Self-fertilization: 2 cells from the same organism
    • Cross-fertilization: cells from different organisms
  • The emerging diploid Diploid The chromosomal constitution of cells, in which each type of chromosome is represented twice. Symbol: 2n or 2x. Basic Terms of Genetics zygote Zygote The fertilized ovum resulting from the fusion of a male and a female gamete. Fertilization and First Week undergoes meiosis Meiosis The creation of eukaryotic gametes involves a DNA replication phase followed by 2 cellular division stages: meiosis I and meiosis II. Meiosis I separates homologous chromosomes into separate cells (1n, 2c), while meiosis II separates sister chromatids into gametes (1n, 1c). Meiosis to form haploid Haploid The chromosomal constitution of cells, in which each type of chromosome is represented once. Symbol: n. Basic Terms of Genetics spores Spores The reproductive elements of lower organisms, such as bacteria; fungi; and cryptogamic plants. Anthrax.
  • Spores Spores The reproductive elements of lower organisms, such as bacteria; fungi; and cryptogamic plants. Anthrax germinate to create more haploid Haploid The chromosomal constitution of cells, in which each type of chromosome is represented once. Symbol: n. Basic Terms of Genetics mycelia.

Toxic Products of Fungi

Pathogenic Effect of Fungi

• Mycoses: infectious diseases caused by fungi:
  • Usually do not pose problems in healthy individuals
  • May cause opportunistic infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease in individuals who are immunocompromised immunocompromised A human or animal whose immunologic mechanism is deficient because of an immunodeficiency disorder or other disease or as the result of the administration of immunosuppressive drugs or radiation. Gastroenteritis
• Classes:
  • Superficial mycoses:
    • Oropharynx Oropharynx The middle portion of the pharynx that lies posterior to the mouth, inferior to the soft palate, and superior to the base of the tongue and epiglottis. It has a digestive function as food passes from the mouth into the oropharynx before entering esophagus. Pharynx: Anatomy: commonly seen in infants, elderly, or immunocompromised immunocompromised A human or animal whose immunologic mechanism is deficient because of an immunodeficiency disorder or other disease or as the result of the administration of immunosuppressive drugs or radiation. Gastroenteritis individuals
    • Anogenital area: Vaginal yeast infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease are commonly seen even in healthy individuals.
    • Skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions: keratinophilic fungi (also known as dermatophytes Dermatophytes Tinea infections are a group of diseases caused by fungi infecting keratinized tissue (hair, nails, and skin). These infections are termed dermatomycoses and are caused by the dermatophyte fungi. There are approximately 40 dermatophyte fungi that are part of 3 genera, including Trichophyton, Epidermophyton, and Microsporum. These infections can affect any part of the body but occur most often in warm, moist regions like the groin and the feet. Dermatophytes/Tinea Infections) that affect human skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions, hair, and nails
  • Systemic mycoses: 
    • Develop when fungal spores Spores The reproductive elements of lower organisms, such as bacteria; fungi; and cryptogamic plants. Anthrax are inhaled or introduced into the bloodstream
    • Can manifest in different inner organs, resulting in severe lethal infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease
    • Patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship who are HIV HIV Anti-HIV Drugs positive or immunosuppressed are susceptible to systemic mycoses.
• Examples:
  • Thrush: infection of the oral mucosa Oral mucosa Lining of the oral cavity, including mucosa on the gums; the palate; the lip; the cheek; floor of the mouth; and other structures. The mucosa is generally a nonkeratinized stratified squamous epithelium covering muscle, bone, or glands but can show varying degree of keratinization at specific locations. Stomatitis; Candida Candida Candida is a genus of dimorphic, opportunistic fungi. Candida albicans is part of the normal human flora and is the most common cause of candidiasis. The clinical presentation varies and can include localized mucocutaneous infections (e.g., oropharyngeal, esophageal, intertriginous, and vulvovaginal candidiasis) and invasive disease (e.g., candidemia, intraabdominal abscess, pericarditis, and meningitis). Candida/Candidiasis species
  • Onychomycosis: infection of the nail; Trichophyton rubrum Trichophyton rubrum Dermatophytes/Tinea Infections
  • Dermatophytosis: infection of the skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions ( tinea pedis Tinea pedis Dermatological pruritic lesion in the feet, caused by Trichophyton rubrum, T. mentagrophytes, or Epidermophyton floccosum. Dermatophytes/Tinea Infections, corporis, or cruris)
    • Microsporum Microsporum A mitosporic oxygenales fungal genus causing various diseases of the skin and hair. The species microsporum canis produces tinea capitis and tinea corporis, which usually are acquired from domestic cats and dogs. Teleomorphs includes arthroderma (nannizzia). Dermatophytes/Tinea Infections canis, M. audouinii, M. gypseum
    • Epidermophyton Epidermophyton A fungal genus which grows in the epidermis and is the cause of tinea. Dermatophytes/Tinea Infections floccosum
    • Trichophyton Trichophyton A mitosporic fungal genus and an anamorphic form of arthroderma. Various species attack the skin, nails, and hair. Dermatophytes/Tinea Infections tonsurans, T. mentagrophytes, T. verrucosum, T. schoenlenii
  • Coccidioidomycosis Coccidioidomycosis Coccidioidomycosis, commonly known as San Joaquin Valley fever, is a fungal disease caused by Coccidioides immitis or Coccidioides posadasii. When Coccidioides spores are inhaled, they transform into spherules that result in infection. Coccidioidomycosis is also a common cause of community-acquired pneumonia and can cause severe disease in the immunocompromised. Coccidioides/Coccidioidomycosis: a pulmonary or disseminated fungal infection
    • Coccidioides immitis Coccidioides immitis Coccidioides/Coccidioidomycosis 
    • C. posadasii

Synthesis of Antimicrobials

Some fungi are capable of producing substances that are effective as antimicrobials:

• Penicillin Penicillin Rheumatic Fever from Penicillium notatum
• Cephalosporin Cephalosporin Multidrug-resistant Organisms and Nosocomial Infections from Acremonium
• Streptomycin from Streptomyces griseus
• Griseofulvin Griseofulvin In addition to the 3 other major classes of antifungal agents (azoles, polyenes, and echinocandins), several other clinically important antifungal agents are used, including flucytosine, griseofulvin, and terbinafine. Griseofulvin acts within the stratum corneum of the skin and are used to treat dermatophyte infections of the skin, hair, and nails. Flucytosine, Griseofulvin, and Terbinafine from P. griseofulvum
• 50 of approximately 2,000 substances characterized as antibiotics are used as chemotherapeutics.

Clinical Relevance

Opportunistic fungal infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease

Many fungi are opportunists and are especially pathogenic in patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship who are immunocompromised immunocompromised A human or animal whose immunologic mechanism is deficient because of an immunodeficiency disorder or other disease or as the result of the administration of immunosuppressive drugs or radiation. Gastroenteritis. Opportunistic systemic fungal infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease (mycoses) include candidiasis Candidiasis Candida is a genus of dimorphic, opportunistic fungi. Candida albicans is part of the normal human flora and is the most common cause of candidiasis. The clinical presentation varies and can include localized mucocutaneous infections (e.g., oropharyngeal, esophageal, intertriginous, and vulvovaginal candidiasis) and invasive disease (e.g., candidemia, intraabdominal abscess, pericarditis, and meningitis). Candida/Candidiasis, aspergillosis Aspergillosis Aspergillosis is an opportunistic fungal infection caused by Aspergillus species, which are common spore-forming molds found in our environment. As Aspergillus species are opportunistic, they cause disease primarily in patients who are immunocompromised. The organs that are most commonly involved are the lungs and sinuses. Aspergillus/Aspergillosis, mucormycosis Mucormycosis Mucormycosis is an angioinvasive fungal infection caused by multiple fungi within the order, Mucorales. The fungi are ubiquitous in the environment, but mucormycosis is very rare and almost always occurs in patients who are immunocompromised. Inhalation of fungal spores can cause rhinocerebral or pulmonary mucormycosis, direct inoculation can cause cutaneous mucormycosis, and ingestion can cause gastrointestinal mucormycosis. Mucorales/Mucormycosis, and fusariosis, and typically manifest with rapidly progressive pneumonia Pneumonia Pneumonia or pulmonary inflammation is an acute or chronic inflammation of lung tissue. Causes include infection with bacteria, viruses, or fungi. In more rare cases, pneumonia can also be caused through toxic triggers through inhalation of toxic substances, immunological processes, or in the course of radiotherapy. Pneumonia or fungemia Fungemia The presence of fungi circulating in the blood. Opportunistic fungal sepsis is seen most often in immunosuppressed patients with severe neutropenia or in postoperative patients with intravenous catheters and usually follows prolonged antibiotic therapy. Chronic Granulomatous Disease.

Primary fungal infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease

Caused by inhalation of fungal spores Spores The reproductive elements of lower organisms, such as bacteria; fungi; and cryptogamic plants. Anthrax, which results in pneumonia Pneumonia Pneumonia or pulmonary inflammation is an acute or chronic inflammation of lung tissue. Causes include infection with bacteria, viruses, or fungi. In more rare cases, pneumonia can also be caused through toxic triggers through inhalation of toxic substances, immunological processes, or in the course of radiotherapy. Pneumonia. Different infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease have specific geographic distribution: 

• Coccidioidomycosis Coccidioidomycosis Coccidioidomycosis, commonly known as San Joaquin Valley fever, is a fungal disease caused by Coccidioides immitis or Coccidioides posadasii. When Coccidioides spores are inhaled, they transform into spherules that result in infection. Coccidioidomycosis is also a common cause of community-acquired pneumonia and can cause severe disease in the immunocompromised. Coccidioides/Coccidioidomycosis: Southwestern US, Washington, Northern Mexico, and Central and South America
• Histoplasmosis Histoplasmosis Histoplasmosis is an infection caused by Histoplasma capsulatum, a dimorphic fungus. Transmission is through inhalation, and exposure to soils containing bird or bat droppings increases the risk of infection. Most infections are asymptomatic; however, immunocompromised individuals generally develop acute pulmonary infection, chronic infection, or even disseminated disease. Histoplasma/Histoplasmosis: Eastern and Midwestern US and parts of Central and South America, Africa, Asia ASIA Spinal Cord Injuries, and Australia
• Blastomycosis Blastomycosis Blastomycosis is an infection caused by inhalation of the spores of the fungus, Blastomyces. Blastomyces species thrive in moist soil and decaying material and are common in the Ohio and Mississippi River valleys and the Great Lakes regions of the United States and Canada. Although most patients are asymptomatic, some can develop pneumonia. Blastomyces/Blastomycosis: confined to North America and Africa
• Paracoccidioidomycosis Paracoccidioidomycosis Paracoccidioidomycosis (PCM) is an endemic fungal infection caused by Paracoccidioides brasiliensis and P. lutzii. The fungus is geographically distributed across Mexico and South and Central America. Transmission is by inhalation, and most infections are asymptomatic. Paracoccidioides/Paracoccidioidomycosis: South America