Fungi Lecture 6 PDF

Fungi Fungal Diseases  Fungal Cell Mycology Kingdom Fungi Eukaryotic Rigid cell wall - Chitin - Glucan Unicellular Multicellular Pathological, beneficial  Classification of Fungi Yeasts – single-cell organisms Mold - Multicell...

Fungi Fungal Diseases  Fungal Cell Mycology Kingdom Fungi Eukaryotic Rigid cell wall - Chitin - Glucan Unicellular Multicellular Pathological, beneficial  Classification of Fungi Yeasts – single-cell organisms Mold - Multicellular organisms Mold Characteristics of Fungi Budding process of yeast  Life Cycle of Fungi Both sexual and asexual reproduction in fungi occurs by the formation of spores. Asexual spores are formed by the hyphae of one organism. Sexual spores result from the fusion of nuclei from two opposite mating strains of the same species of fungus.  Sexual Reproduction 1. Plasmogamy. A haploid nucleus of a donor cell (+) penetrates the cytoplasm of a recipient cell (-). 2. Karyogamy. The (+) and (-) nuclei fuse to form a diploid zygote nucleus. 3. Meiosis. The diploid nucleus gives rise to haploid nuclei (sexual spores), some of which may be genetic recombinants. Life cycle of Rhizopus, a zygomycete  Nutritional Adaptations Grow better in pH 5 Almost all molds are aerobic Most yeasts are facultative anaerobes Resistant to osmotic pressure Are often capable of metabolizing complex carbohydrates, such as lignin (a component of wood).  Fungal Diseases - Mycoses Systemic Subcutaneous Cutaneous Superficial Opportunistic  Systemic mycoses Blastomycosis - Blastomyces dermatitidis Coccidioidomycosis - Coccidioides immitis and C. posadasii Histoplasmosis - Histoplasma capsulatum Paracoccidioidomycosis - Paracoccidioides brasiliensis  Blastomycosis Pathogen Blastomyces dermatitidis Route of infection - inhalation of conidia. Symptoms - from pneumonia or from dissemination to multiple organs, most commonly the skin. Diagnosis: - chest x-ray, - laboratory identification of the fungi. Treatment with itraconazole, fluconazole, or amphotericin B.  Coccidioidomycosis Asymptomatic pulmonary disease (in most people) Self-limited flulike illness Hypersensitivity to Coccidioides immitis antigens may manifest as: Erythema nodosum Arthritis Conjunctivitis Erythema multiforme Extrapulmonary sites - skin, soft tissues, bones, joints, and meninges.  Histoplasmosis H. capsulatum - pulmonary and disseminated infections H. capsulatum var. duboisii – skin and bone infection Symptoms of Histoplasmosis Fever Cough Fatigue (extreme tiredness) Chills Headache Chest pain Body aches  Paracoccidioidomycosis South American blastomycosis Mucocutaneous: Infections most often involve the face, especially at the nasal and oral mucocutaneous borders. Lymphatic: Cervical, supraclavicular, or axillary nodes enlarge. Visceral: Typically, focal lesions cause enlargement mainly of the liver, spleen, and abdominal lymph nodes.  Subcutaneous Mycoses 1. Mycetoma 2. Sporotrichosis 3. Phaeohyphomycosis 4. Chromoblastomycosis  MYCETOMA (Maduromycosis=Madura foot) Causative agents - Saprophytic fungi (Eumycetoma), Actinomyces (Actinomycetoma) Post-traumatic chronic infection of subcutaneous tissue. Characterized by draining sinuses, granules and swelling. Caused by a number of different fungi and actinomycetes. First case seen in Madura region of India.  Source of infection: soil Mode of infection: trauma Infection is acquired following trauma to the skin by plant materials from trees, shrubs or vegetation debris. Feet are the most common site for infection and account for at least two-thirds of cases. Other sites include the lower legs, hands, head, neck, chest, shoulder and arms. More seen in rural areas (in farmers, walking bare-foot in agricultural land or city parks).  Clinical findings Site(s): Feet, lower extremities, hands Findings: Abscess formation, draining sinuses containing granules deformities Dissemination: Muscles and bones Laboratory Diagnosis: Clinical specimen: Tissue biopsy Serosanguinous fluid containing the granules Treatment: Combining miconazole and surgery may prove useful in effectively treating the disease.  Sporotrichosis Caused by Sporothrix schenckii The initial lesion is a granulomatous nodule that will ulcerate and become necrotic. Multiple subcutaneous nodules occur along the lymphatic vessels.  Lab Diagnosis Direct microscopic examination Culture method is done on SDA with antibiotics at 25 degree (colonies are black and shiny then become wrinkled and fuzzy with age). Under the microscope Serology - latex agglutination test Culture  Phaeohyphomycosis Cutaneous phaeohyphomycosis of the face caused by Wangiella dermatitidis. Characterized by the presence of brown pigmented fungal elements caused by a number of different fungal species The fungi are usually pigmented dark brown In rare instances infections may become invasive systemic (invading various organs) Cutaneous phaeohyphomycosis and/or cerebral. of the forearm caused by Exophiala jeanselmei. Distribution: Worldwide  Cutaneous Mycoses Dermatophytosis - disease of the nails, hair, and/or stratum corneum of the skin caused by fungi called dermatophytes. Dermatomycosis - more general name for any skin disease caused by a fungus. Infection of the skin, hair or nails caused by a group of keratinophilic fungi, called dermatophytes.  DERMATOPHYTES (3 Genera) Disease of the skin, hair, or nails Keratinophilic and keratinolytic Dermatophytes invade only the upper outermost layer of the epidermis, the stratum corneum. Trichophyton - infections on skin, hair, and nails Microsporum - infections on skin and hair Epidermophyton - infections on skin and nails  DERMATOPHYTOSIS Infection is named according to the anatomic location involved: - Tinea corporis: small lesions occurring anywhere on the body Tinea barbae: Ringworm of the bearded areas of the face and neck. - Tinea pedis : "athlete's foot". Infection of toe webs and soles of feet. - Tinea unguium (onychomycosis) : nails - Tinea capitis : head. Frequently found in children  Ecology of Dermatophytes The source of infection Anthropophilic - Person-to-person transmission through contaminated objects (combs, etc.) Zoophilic - Associated with animals. Direct transmission to humans by close contact with animals. Geophilic - Usually found in soil (soil saprophytes). Transmitted to humans by direct exposure.  Laboratory Diagnosis The laboratory diagnosis of dermatophytoses relies on the demonstration of fungal hyphae by direct microscopy of skin, hair, or nail samples and the isolation of organisms in culture. Treatment Therapy consists of thorough removal of infected and dead epithelial structures and application of a topical antifungal chemical. To prevent reinfection the area should be kept dry, and sources of infection, such as an infected pet or shared bathing facilities, should be avoided.  Superficial Mycoses Colonize the keratinized outer layers of the skin, hair, and nails Asymptomatic mostly Cosmetic concern Pityriasis (Tinea) Versicolor Tinea Nigra White Piedra Black Piedra  Pityriasis (Tinea) Versicolor Causative agent is Malassezia furfur. The lesions are small hypopigmented or hyperpigmented macules. Laboratory Diagnosis Direct visualization of the fungal elements Microscopic examination of epidermal scales Culture Treatment consists of the use of topical azoles or selenium sulfide shampoo.  Tinea Nigra Causative agent - Hortaea werneckii Irregular, pigmented (brown to black) macule, usually on the palms or soles. Diagnosis Microscopic examination of skin scrapings. Treatment includes topical therapy.  Opportunistic Mycoses Mucormycosis - Rhizopus and Mucor – leukemia, diabetes mellitus patients Aspergillosis –Aspergillus - lung diseases or cancer patients Cryptococcosis – Cryptococcus - fatal in AIDS patients Candidiasis - Candida albicans, causes vulvovaginal candidiasis Candida spp. Cryptococcus neoformans  Practical Application of Fungi Aspergillus niger is used to produce citric acid. Saccharomyces cerevisiae is used to make bread and wine; hepatitis B vaccine. Trichoderma is used to produce the enzyme cellulase to remove plant cell walls to produce a clear fruit juice. Paecilomyces fumosoroseus is used as a biological alternative to chemicals to kill termites hiding inside tree trunks. References GJ. Tortora, BR. Funke CL. Case, Microbiology, an Introduction, 2018, chapter 12; Murray, Basic Medical Microbiology, Part IV