BIOL 2421 Microbiology Lecture Notes: Fungi Dr. Weis
Fungi belong to the Domain Eukarya in the Kingdom Fungi and there are millions of species, but only about 400 cause disease.
The major pathogenic species are classified within four phylum, ending in –mycota.
Phylum Zygomycota
. Phylum Basidiomycota
Phylum Ascomycota
Phylum Deuteromycota – the imperfect fungi
Overview:
Fungi are plant like, spore-bearing, primarily
terrestrial organisms that lack chlorophyll so they must absorb food from
others, so they are carbon heterotrophs.
Therefore, they can live in dark habitats and can grow in any direction.
Fungi reproduce and spread by means of spores (conidia), which can remain in the environment for years.
The body or vegetative [non-reproductive]
structure of a fungus is called the thallus.
If a fungus can produce both yeast like thallus and mold like thallus, it
is considered to be dimorphic.
Yeast like thallus:
Small
Globular
Single cell
Mold like thallus:
Large
Long tubular
Branched
There are basically three types of fungi: mushrooms, moulds, and yeasts.
Yeasts are unicellular fungi that have a single nucleus and reproduce either
Asexually by budding or sexually through spore formation
Yeasts are larger than bacteria and are commonly spherical to egg shaped
Usually are Facultative anaerobes and prefer warmer temperatures
Moulds consist of long, branched, small threads known as hyphae. These hyphae typically occur as a networked mass known as mycelium.
Hyphae can be characterized several ways
Uninterrupted branches = coenocyte
Cross cell walls = septate
Hyphae consist of an outer cell wall, plasma membrane, and an inner lumen which contains cytosol and organelles
Moulds are aerobic and prefer environmental, room temperature
Specific Fungal Characteristics
Cell wall consists of chitin, chitosan, glucan, mannan, and others.
Cell membrane has an ergosterol (which replaces cholesterol)
Nucleus that contains several diploid chromosomes
Nuclear membrane that resembles a eukaryotic nucleus
Cytoplasm is similar to plants, but differs in organelles
(i.e. no chlorplasts, different protein that makes microtubules)
Non vascular, non motile organisms
Reproduction is by means of spores produced sexually (meiotic) or asexually (mitotic)
Vegetative body may be unicellular (yeast) or composed of threads called hyphae
Nutritional Status of Fungi
* Saphrophytes
* Parasites
* Mutualists (symbionts)
Saphrophytes
Use non-living organic material
Scavengers of the ecosystem that release hydrolytic enzymes for digestion
Recycle Carbon, Nitrogen, and essential mineral nutrients
Parasites
Use organic material from living organisms
Parasitize plants, animals, and humans
Mutualists
Beneficial relationship with other living organisms, primarly with plants
“Good” Fungus – useful to humans
^ Yeasts à baking and brewing
^ Antibiotics à penicillin and cephalosporin
^ Other drugs à cyclosporin
^ Organic acids à citric acid
^ Steroids and hormones à “the pill”
^ Stinky Cheeses à Blue cheese, Roquefort
^ Experimental organismsà metabolic pathways used as study tool
Parasitic Fungi
Cause human disease either directly or indirectly through their toxins
True parasitic fungi exhibit dimorphism = another phase inside the human body to get around the immune system, such as a yeast phase or spherule phase
Fungal diseases can be caused by
Actual fungus infection due to growth of the organism
Allergic reactions
Fungal Toxins
Dimorphic Fungi
Two forms
a) room temperature = mycelial, filamentous form, create spores
b) body temperature = yeast or spherule form, usually within WBCs
Laboratory Methods Used to Identify Fungi
Fungi in tissue preparations
Various
Stains used: KOH, Eosin,
Culture on Sabauroud’s agar or Mycosal Agar
Cellular Morphology of Hyphae, spore, yeast
Innate Immunity of humans to Fungal Infections
* skin : Fatty acids, pH, epithelial turnover, normal flora
* respiratory: cilia
Reproductive Cycle of Fungi
Sexual State (meiotic) is referred to as the teleomorph, mating types are “+” and “-“
Asexual State (mitotic) is referred to as the anamorph
Many Fungi have both states, that is, spores (conidia) are produced by both cycles
Conidia can be large and complex (macroconidia) or small & simple (microconidia)
When conidia are enclosed in a sac, they are termed endospores
Conidia presence, size, shape, location are the major features used for lab Id
Sexual Reproduction (Telopmorph)
a) involves the union of two compatible nuclei
b) Life cycle
* Plasmogamy – cell fusion
* Karyogamy – nuclear fusion
* Meiosis
c) Sex organs in fungi are called gaemtangia and may be differentiated into male
female organs that can bear either differentiated sex cells (gametes)
* If a single mycelium is capable of reproducing sexually = homothallic
* If two mycelia are required to reproduce sexually = heterothallic
The four major phyla of Fungi are based on the method of producing sexual spores
1) Zygomycota: sexual spores are thick walled resting spores called zygospores
2) Ascomycota: spores borne internally in a sac called an ascus
3) Basidiomycota: spores borne externally on a club-shaped structure called basidium
4) Deuteromycetes: have no known sexual state in their life cycle
Asexual Reproduction
Most common method of asexual reproduction is by means of spores
* In Zygomycota: asexual spores may be delimited within a sac-like
structure called sporangia (sporangiophore)
* In Ascomycota: asexual spores may be borne at the tips or sides of hyphae called conidia (conidiophore)
* Basidiomycota do not produce asexual spores
Yeast Reproduction
Simple splitting of a cell into two daughter cells called fission
Small outgrowth is formed from the parent cells called budding
Buds can remain attached to one another and the parent cell in an arrangement called a pseuohyphae
If fungi pass resistance barriers of the human body, they establish infections that can be classified according to the tissue levels colonized:
* Superficial: outermost layers of the skin and hair
* Cutaneous: deeper into the epidermis, invasive to hair and nails
* Subcutaneous: infections involving the dermis, SC, muscles, fascia
* Systemic: originate in lungs, may spread to other organ systems
* Opportunistic: infections in immunocompromised individuals
HUMAN MYCOSES
FUNGAL INFECTIONS OF THE SKIN
* Sporotrichosis
* Candidiasis
* Tinea
Sporotrichosis
Sporothrix schenckii
Dimorphic fungus with a yeast like appearance, cigar shaped
Worldwide, common in tropical and subtropical areas
Transmission: direct inoculation of conidia into the skin
Usually seen with gardeners and others working with soil
Clinical Course:
Erythematous papulonodular lesions that may ulcerate and drain
Lymphocutaneous (lymphatics but not in lymph nodes)
Osteoarthritis and tenosynovitis of the hand, elbows, ankles, knees
Pulmonary (if inhale conidia)à plural effusion
CNS: Meningitis [rare]
Disseminated: liver, spleen, bone marrow, colon
DX: IFA, special staining of histopath sections
Brain-Heart Infusion
TX: Antifungals [Oral azoles, Amphoteracin B., Potassium Iodide]
Candidiasis
Thin walled small yeasts that reproduce by budding
10 species cause disease: C. albicans,
Reservoir: soil, inanimate objects, food, and hospital environments
Source: normal commensals of humans
Diseases seen in individuals with immunosupression, post surgery, post antibacterial treatments, organ transplantation patients
Clinical Disease Course:
Candidiasis of skin and mucosal surfaces
Invasive candidiasis
Miscellaneous
Candidiasis of MM
* Cutaneous
* Chronic mucocutaneous
* Esophagitis
* Onychomycosis
*Oropharyngeal
* Vulvovaginitis
Invasive Candidiasis
Invasion past the skin that creates systemic infection
Usually only seen in immunocompromised patients
* Peritonitis
* Osteomyeltitis / Athritis
* Pancreatic
* Hepatosplenic
* Urinary
* Eye
Miscellaneous
Chronic candidiasis
* GIà bloating, nausea, diarrhea
* Vaginal à puritis, burning, abnormal discharge
* Respiratoryà allergy = sneezing, wheezing
* CNS à anxiety, depression, memory deficits
Neonatal: overgrowth in mouth à Thrush
DX: Id organism
TX: Antifungals [-azoles]
Tinea Dermatophytes: Ringworm
Colonize the hair, nails, and outer layer of skin (stratum corneum) and grow on the keratin.
Cause annular lesions with erythematous and spreading borders with central clearing
Various species that colonize specific areas
Tinea capitis: ringworm of the scalp
Tinea corporis: ringworm of the body
Tinea cruris: ringworm of the groin
Tinea pedis: ringworm of the foot [Athlete’s foot]
Tinea unguium: ringworm of the nails
Three fungi are involved with Cutaneous mycosis
* Trychophyton
* Microsporum (affects hair and skin)
* Epidermophyton (affects skin and nails)
DX: Id organism on selective media or skin scrapings
TX: Antifungal [griseofulvin, systemic -azoles]
FUNGAL INFECTIONS OF THE NERVOUS SYSTEM
Cryptococcosis
37 species of cryptococcus, only one major human disease species:
Cryptococcus neoformans
Encapsulated, round yeast-like organism
Opportunistic infection of immunocompromised individuals
[HIV, organ transplant, cancer, DM, Autoimmune dz]
Distribution: worldwide
Transmission: inhalation of aerosolized spores
Virulence factor: phenoloxidase enzyme
Polysaccharide capsule
Clinical course: Organism may stay locally in the lungs
Pulmonary Forms are acute and chronic
Acute = Respiratory distress
Chronic = nodules, pneumonia, pleural effusion
Disseminated à
CNS à meningitis
Cutaneous à ulcerative papules/pustules
Eyeà endopthalmitis, chorioretinitis, conjunctivitis
Heartà pericarditis, endocarditis, myocarditis
GIà gastroenteritis, hepatitis, cholecystitis
Renal à abscess
Boneà arthritis, osteomyelitis
DX: Id organism in fluid
Culture agent: yeast cells
Serology: Latex Agglutination
Histopathology
TX: Antifungals [Fluconozole, itroconozole, Amphotericin B]
FUNGAL INFECTIONS OF THE CARDIOVASCULAR SYSTEM
Zygomycosis refers to the angiotrophic infection produced by various zygomycetes species: Absidia, Rhizomucor, Rhizopus. [Rhizomucor = worst]
Reservoir: soil, decaying vegetables
Associated with immunocompromised patients:
Burn, DM, HIV, blood cancers, malnutrition
Clinical Course: Invades arteries resulting in embolization and necrosis
Can spread to respiratory, GI, skin, and other areas
Forms of the disease
a) Rhinocerebral: usually seen in DM
involves orbital structures
sinus and internal carotid artery thrombosis
b) Pulmonary: usually occurs in neutropenic individuals
cough and dyspnea with hemoptysis
segmental consolidation of lungs
c) GI: usually affects patients with severe malnutrition
intra-abdominal abscesses
d) Cutaneous: usually seen with skin trauma, burns
necrotic lesions that go from epidermis downward
e) Other areas affected: bone, urinary tract, heart
DX: At autopsy
Histopathology
Id organisms from scrapings or discharges
Culture organism on Sabouraud’s agar
TX: Antifungal [Amphotericin B]
Most cases are fatal
FUNGAL INFECTIONS OF THE RESPIRATORY SYSTEM
Aspergillosis
Aspergillus sp.
[flavus,
Reservoir: ubiquitous in environment, soil, decaying vegetation
Transmission: Inhalation of fungal spores
Opportunistic in patients with respiratory disease: TB, bronchiectasis
Affects susceptible individuals with lowered immune defenses
Chronic disease, chemotherapy, disruption of normal flora, CCS
Clinical disease forms:
Allergic Bronchopulmonary aspergillosis à sinuses and lungs
Pulmonary aspergillosisà within lungs
Invasive aspergillosisà
CNS
Sinonasal
Osteomyelitis
Endocarditis
Renal abscesses, urinary tract fungus balls
Cutaneousà post surgical, burn victims, IV catheters
Otomycosis
DX: Direct examination of organism in fluids, sputa, tissue (cytology)
Histopathology
Culture organism on Sabouraud’s agar
TX: Antifungals [Itraconozole, Voriconazole, Amphotericin B]
Px: Mortalitly rate is 50-100%
Coccidioidomycosis
Coccidioides immitis dimorphic fungus
Reservior: Western hemisphere, in US desert areas [Arizona, NM, TX, CA]
Arid, alkaline soils, hot summers, few freezing, early rainfalls
Outbreaks à dust storms, earthquakes
Transmission: Inhalation of fungal spores (arthroconidia)
Spores then transform into spherical cells called spherules that release to endospores to cause an acute respiratory infection.
Immunocompromised patients have greater chance of more severe disease form
Clinical Disease courses
Asymptomatic à 50% of patients
Acute Symptomatic à cough, chest pain, SOB, fever, fatigue
Pneumonia in immunocompromised patients
Skin à papular rash, erythema nodosum
Chronic Pulmonary à pulmonary nodules
Extra Pulmonary / Disseminated
Chronic skin diseaseà keratotic and ulcerative/ abscessed S.C.
Joints / Bones -à synovitis, lytic lesions in the axial skeleton
Meningeal Dzà hydrocephalus
Others: can affect any organ:
GI, urogenital, internal body cavity linings, thyroid, adrenal
DX: CF
Radiography
Direct examination of specimens: fluids, sputum, tissue cytology
Histopathology
Isolation of organism on BHI or IMA to Id arthroconidia
TX: Antifungals [Amphotericin B]
PX: 90% of cases resolve spontaneously, unless immunocompromised
Paracoccidioidomycoses
Paracoccidiodes brasiliensis
Reservoir: Soil and wood, primarily in South America
Transmission: Inhalation of conidia
Clinical Course:
Asymptomatic as fungus can lay dormant for several years, will reappear
If immunosuppressed
Mucous membranes: painful ulcerations of the mouth and oropharynx
Pulmonary: nodular infiltrates affecting central and basal zones of lungs
Clinical picture mimics TB
Skin: ulcerative, crusty lesions that will infiltrate the S.C.
Others: may affect other organs such as
GI, liver, bones, CNS, male genitourinary tract
DX: Direct examination of specimens: fluid, sputum, tissue cytology
Histopathology: budding yeast with blastoconidia of various sizes
Isolation with Sabouraud dextrose agar, BHI
TX: Antifungals [-azoles]
PX: good if treated, relapse is possible
Blastomycoses
Blastomyces dermatitidis dimorphic fungus, heterothallic ascomycete
Endemic in South eastern and South central states of North America [Mississippi, Ohio river valleys]
Reservoir: Soil, rotting wood, feces of birds and bats
Transmission: inhalation of conidia à yeast form once in lungs
Clinical disease forms:
Asymptomatic: 50% of infections
Acute Pulmonary: lobar or segmental consolidation, mimics bacterial pneumonia
Chronic Pulmonary: lobar infiltrates mimics bronchogenic carcinoma
Skin: ulcerative lesions, subcutaneous nodules that abscess
Bone / Joint: long bones, ribs, vertebrae à osteolytic
Genitourinary Tract: prostate and epididymis
Other organs: CNS, pericardium, adrenal gland, GI
DX: Direct examination of clinical materials: fluidsà sputum, prostate, tissue
Histopathology
Id blastoconidia on culture of Sabauroud glucose agar, BHI
TX: Antifungals [Amphotericin B, -azoles]
PX: some spontaneous resolution, TX necessary especially for CNS, bone
Histoplasmosis
Histoplasma capsulatum dimorphic fungus
Reservoir: soil
Transmission: inhalation of microconidia that transform into yeast form
Clinical Course
Subclinical and benign in normal hosts: 50-90%
Disseminated and potentially fatal in immunocompromised individuals
Acute forms of the disease
Self-limited: flu like symptoms
Pulmonary: pneumonitis, calcification, buckshot appearance on Radiograph
Pericarditis: pericardial fluid, associated intrathoracic adenopathy
Rheumatologic: arthralgia, arthritis, erythemia nodosum
Chronic Pulmonary: mimics TB
Fibrosing Mediastinitis: intense deposition of fibrotic tissue in mediastinum
Affects other structures such as vena cava, esophagus, trachea
Disseminated Forms of Histoplasmosis
Lymph Nodes: Lymphadentitis
Bone Marrow: Anemia, leukopenia, thrombocytopenia
Heart: Endocarditis
Adrenal Glands: enlargement, Addison’s Dz
CNS: chronic meningitis, cerebritis
GI: oral ulcers, small intestinal ulcers
Eyes: uveitis, choroiditis
Skin: papular to nodular rash
Genitourinary: hydronephrosis, prostatitis, ulcers in bladder, penis
DX: Direct Id of fungi in bone marrow, sputum
BHI agar
Ag detection in urine or serum
Histopathology: id organism in reticuloendothelial cells (macrophages)
TX: Antifungals [fluconazole]
PX: most are self limited and do not require treatment
Treatment important in respiratory forms and disseminated forms
DISEASES CAUSED BY ENVIRONMENTAL MOULDS
Allergic Reactions to Fungi
Wheezing, cough, sinus congestion, itchy nose, sore throat, rhinorrhea
Require prior exposure and then re-exposure to fungal antigens
Fungal Toxins (Mycotoxins)
Ingestion of toxin
* Ergotism: Claviceps purpurea
limb gangrene, hallucinations, death
ingestion of rye products contaminated by ergot alkaloids
* Aflatoxins: Aspergillus flavus
ingestion of peanut meal contaminated with aflatoxins
* Zearalenone: Fusarium graminearum
ingestion of estrogen-like steroid
associated with episodes of precocious puberty
Note all toxins are bad: Griseofulvin: Penicillium griseofulvum kills other fungi, topical use
ANTIFUNGAL AGENTS:
I. Macrolides [Polyene antibiotics]
Amphotericin B: binds to ergosterol in plasma membrane causing a derangement
Of the membrane integrity and leakage of cytoplasmic contents
Nystatin: binds to ergosterol and disrupts plasma membrane, topical only
II. Azoles
Block ergosterol synthesis at one or more sites to cause selective leakage
May also disrupt chitin synthesis
All effects are due to the binding of the drug to cytochrome P-450
Drug examples include:
Clortrimazole [topical]
Fluconazole [oral, topical]
Itraconazole [oral]
Ketaconazole [oral, topical]
Miconozole [IV, intrathecal, oral]
III. Allylamines
Naftifine and Terbinafine
binds to and inhibits squalene epoxidase which blocks ergosterol synthesis
IV. Pyrimidine Analogs
Flucytosine à fluracil
Which can be incorporated into RNA in place of uracil to inhibit protein syn
Fluracil à 5-fluordeoxy-uridylic acid which inhibits thymidylate synthetase, thus
Blocking DNA synthesis
V. Misc.
Griseofulvin: causes distruption of the mitotic spindle by interacting with the
Polymerized microtubules through binding to that protein
Systemic administration
Others: Topical administration, no known actual function
* Haloprogin
* Cicloprix olamine
* Tolnaftate