Mycology

Introduction

Fungi are the subject of mycology. It belongs to biology or microbiology. It talks about the characteristics of fungi, how they affect people, and the diseases they cause. Prevention, management, and treatment of fungal diseases are also included in mycology.

Structure of Fungi

Eukaryotic means that fungi are similar to mammalian cells. A cytoplasmic membrane separates the cytoplasm and cell wall of fungi. Additionally, mitochondria, nuclear membranes, and real nuclei are present in fungal cells. Fungi are composed of the following parts:

•  Fungal cell wall
  • Fungi have a hard cell wall composed of glucans, mannans, and complex polysaccharides, most notably chitin (rather than peptidoglycan as in bacteria), making them resistant to antibiotics that inhibit peptidoglycan formation, such as penicillin.
•  Fungal cell membrane
  • The cell membrane protects the cellular components. Fungi have ergosterol in their cell membranes, whereas mammals have cholesterol. This differential in membrane sterols underpins the selective action of amphotericin B and azole medicines (e.g. fluconazole) on fungus.
• Fungal cellular components
  • Cytoplasm, eukaryotic nuclei, mitochondria, and many vacuoles are all examples of organelles. Cholorplasts are not found in fungi. The nucleus is surrounded by a nuclear membrane.

Fungal Forms

• Hyphae (mould):
  • These are filamentous subunits of moulds and mushrooms. A mass (or colony) of hyphae is a mycelium. An organized body of hyphae is a fruiting body (e.g. a mushroom).
• Yeasts:
  • Yeasts are single-celled fungi which are generally round to oval shaped.

Classification of Medically Important Fungi

Fungi can be classified on various bases, they are:

• Morphological classification
• Systematic classification

Morphological Classification

The morphological classification of medically important fungi is tabulated and described below:

• Yeast:
  • Yeasts are unicellular fungi having spherical or ellipsoidal cells. They reproduce by budding. Cryptococcus neoformans is the only important pathogen in this group.
• Yeast like Fungi: 
  • They grow in two ways: as yeasts and as long filamentous cells united end to end to form a pseudomycelium. Candida albicans is one such instance.
• Filamentous fungi or Moulds: 
  • They are mycelial and filamentous fungus. They develop mycelium as long filaments or hyphae that branch and interlace (a meshwork). They reproduce by producing diverse spores. Vegetative mycelium is the component of mycelium that grows on and penetrates the substrate, taking nutrients for growth. Aerial mycelium is the component of mycelium that protrudes into the air. Trychophyton, microsporum, and epidermophyton are the pathogenic members.
• Dimorphic fungi: 
  • ​​​​​​​Depending on the temperature, dimorphic fungus can exist as yeasts or molds. Dimorphic fungi are molds (mycelial form) at room temperature (25°C) or in soil, but yeasts at body temperature (37°C) or in mammalian bodies. Histoplasma capsulatum, Sporotrichum, Blastomyces dermatitidis, and Coccidiodes immitis are pathogenic members of this group.

Systematic Classification:

Based on sexual spore formation, fungi are classified into four classes:

• Phycomycetes: 
  • They are non-septate hyphae fungus. They produce endogenous asexual spores (sporangiospores) within sac-like structures known as sporangia. There are also sexual spores, which come in two varieties: oospore and zygospore.
• Ascomycetes: 
  • Within a sac, they produce sexual spores (ascospores). This sac is known as an ascus. Yeasts and filamentous fungus are among them. They produce septate hyphae.
• Basidiomycetes: 
  • They reproduce through sexual reproduction. Basidiospores are produced at the basidium's tip. They produce septate hyphae.
• Fungi Imperfecti: 
  • They are a group of fungi whose sexual stages have yet to be identified. Sporothrix schenkii, for example.

Fungal Infections

Almost all of the fungi connected to human illnesses are found in nature. Nevertheless, the destruction of the skin's and the mucosa's protective barriers leads to fungal infections. Most fungal infections are small and self-resolving. However, a few fungi can make otherwise healthy people ill. Fungal diseases called mycoses are frequently classified as:

• Superficial mycoses:
  • ​​​​​​​These are surface infections that affect only the outermost layer of the skin and hair. Malassezia furfur, Tinea nigra, and Exophiala werneckii, for example, cause the infection. Pityriasis versicolor is a yeast infection that causes scaly patches on the skin.
• Cutaneous mycoses:
  • ​​​​​​​These are fungal infections that have spread deeper into the epidermis. Dermatophytes (Microsporum, Epidermophyton) and Candida are responsible for the infection. Dermatophytes and Trichophyton cause (known as ringworm).
• Subcutaneous dermatophytosis mycoses:
  • Infections of the dermis, subcutaneous tissue, muscle, and so on. Phialophora and Madurella fungi induce subcutaneous infection.
• Systemic mycoses:
  • ​​​​​​​These infections are primarily caused by inhalation and originate in the lungs. Soil fungus are the most common cause of this sort of infection. Systemic mycoses are caused by fungi such as Histoplasma capsulatum, Blastomyces dermatitidis, Mucor, Aspergillus spp., and others.
• Opportunistic mycoses:
  • ​​​​​​​Opportunistic fungus causes this form of infection. Low-virulence fungi commonly infect humans with weakened immune systems. Invasive aspergillosis, for example, is caused by Aspergillus fumigatus. The organism invades blood arteries in immunocompromised persons, causing thrombosis and infarction. Mucormycosis is caused by Mucor and Rhizopus. These pathogens are opportunistic. They primarily infect ketoacidotic diabetics and leukemic patients.

Prevention and Control of Fungal Infection

The contact and invasion of tissues and organs by fungi results in fungal infection. Environmental exposure may lead to outbreaks of fungi-related diseases.

Although common, fungus infections can be challenging to identify and treat. As a result, the following preventative and remedial measures for fungi should be used:

• Hand washing is one of the most effective strategies to prevent the spread of fungal infections.
• Avoid infected persons since they are more likely to spread the infection.
• Personal objects such as clothing, towels, shoes, socks, or anything else should not be shared with others, especially suspected or sick people.
• Before travelling to a public place, a fungal-infected area should be covered up.
• Fungal disease should be treated as soon as it is identified.
• Medication should be taken in accordance with the clinician's recommendations.

Treatment with Antifungal Drugs

It is challenging to treat fungal illnesses in humans because antifungal medications that block DNA, RNA, or protein synthesis may have the same impact on human cells. The following medications are used to treat fungal infections:

• Amphotericin B:
  • It is an antifungal polyene that is delivered intravenously (IV). It is the first-line treatment for most life-threatening fungal infections.
• 5-Fluorocytosine (5-FC, flucytosine):
  • It is primarily used in the treatment of cryptococcal meningitis in conjunction with amphotericin B.
• Ketoconazole:
  • It is an imidazole that is taken orally. It can help with chronic mucocutaneous candidiasis and a variety of other cutaneous infections. It has no effect on Aspergillus infections.
• Fluconazole:
  • It is a triazole antifungal systemic medication. It is used to treat systemic candidiasis (e.g. candidemias).
  • Itraconazole
  • It is an imidazole medication that is taken orally.
  • It can be used to treat Aspergillus infections, moderate to severe histoplasmosis, and blastomycosis.
• Griseofulvin:
  • It is a microtubule inhibitor that is taken orally.
  • Although it is effective against dermatophytes, it may aggravate yeast infections.
• Nystatin:
  • It is applied topically, intravaginally, or orally to treat yeast infections or to inhibit yeast growth in compromised patients' gastrointestinal tracts.

Antifungals used to treat dermatophytic infections include miconazole, clotrimazole, econazole, ciclopirox, olamine, naftifine, haloprogin, and terbinafine.