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Fungi & Systemic Mycoses Alfred Lewin References Schaechter et al. Mechanisms of Microbial Disease Kobayashi et al. Medical Microbiology – PowerPoint PPT presentation

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Title: Fungi

Fungi Systemic Mycoses
  • Alfred Lewin

References http// Schaechter
et al. Mechanisms of Microbial Disease Kobayashi
et al. Medical Microbiology
Pizza Mushrooms
  • Domain Eukarya
  • Kingdom Fungi
  • Phylum Basidiomycota
  • Class Hymenomycetes
  • Order Agricales
  • Family Agricaceae
  • Genus Agricarus
  • Species bisporus

Characteristics of fungi
  • A. eukaryotic, non- vascular organisms
  • B. reproduce by means of spores, usually
  • C. both sexual (meiotic) and asexual
    (mitotic) spores may be produced, depending on
    the species and conditions
  • D. typically not motile, although a few (e.g.
    Chytrids) have a motile phase.
  • E. like plants, fungi have an alternation of

More Characteristics of Fungi
  • F. vegetative body may be unicellular (yeasts)
    or composed of microscopic threads called hyphae
  • G. cell walls similar in structure to plants
    but differ in chemical composition-fungi cell
    walls are composed of mostly of chitin-plant cell
    walls are composed mostly of cellulose (plus
    lignin in secondary walls)
  • H. cytoplasmic ultrastructure broadly
    similar to plants cells, but differ significantly
    in kinds of organelles and their structures.

Even more fungal facts
  • I. fungi are heterotrophic ( other
    feeding, must feed on preformed organic
    material), not autotrophic ( self feeding, make
    their own food by photosynthesis).
  • - Unlike animals (also heterotrophic), which
    ingest then digest, fungi digest then ingest.
  • -Fungi produce exoenzymes to accomplish this.
  • J. Most fungi store their food as glycogen
    (like animals). Plants store food as starch

Final Fun Facts on Fungi
  • K. Fungal cell membranes have a unique sterol,
    ergosterol, which replaces cholesterol found in
    mammalian cell membranes
  • L. Tubule proteinproduction of a different type
    in microtubules formed during nuclear division.
  • M. Chitin biosynthesis occurs in fungi.
  • N. Most fungi have very small nuclei, with
    little repetitive DNA.
  • O. Mitosis is generally accomplished without
    dissolution of the nuclear envelope.

Fungal Morphology
Hypae (threads) making up a mycelium
Many pathogenic fungi are dimorphic, forming
hyphae at ambient temperatures but yeasts at body
Antifungal Agents
  • Amphotericin
  • Member of polyene class of antibiotics.
    Antifungal effect due to interaction with sterols
    in membrane, making membranes leaky. Has high
    affinity for ergosterol, but also binds to
    cholesterol - severe side effects.

5-fluorocytosine (5FC) Fungi (but not humans)
d eaminate 5FC to 5-fluorouracil which blocks
RNA and DNA. Synthesis.
Azole antifungal agents Have 5-membered organic
rings that contain either two or three nitrogen
molecules (the imidazoles and the triazoles
respectively). The clinically useful imidazoles
are clotrimazole, miconazole, and ketoconazole.
Two important triazoles are itraconazole and
fluconazole. In general, the azole antifungal
agents are thought to inhibit cytochrome
P450-dependent enzymes involved in the
biosynthesis of cell membrane sterols.
a. Miconazole b. ketoconazole
Griseofulvin Acts interfering with microtubule
assembly. Concentrates inkeratinous structures.
Effective against dermatophytes.
  • Superficial
  • Cutaneous
  • Subcutaneous
  • Systemic
  • Opportunistic

Superficial Mycoses
  • Pityriasis versicolor--pigmented lesions on torso
  • Tinea nigra--gray to black macular lesions often
    on palms
  • Black piedra--dark gritty deposits on hair
  • White piedra--soft whitish granules along hair
  • All are diagnosed by microscopy and are easily
    treated by topical preparations.

Cutaneous Infections
  • Infections of skin and its appendages (nails,
    hair) 20 species of dermatophytes cause

Subcutaneous mycoses
  • Subcutaneous infections - over 35 species
    produce chronic inflammatory disease of
    subcutaneous tissues and lymphatics. e.g.
    sporotrichosis - ulcerated lesions at site of
    inoculation followed by multiple nodules -
    caused by a dimorphic fungus Sporotrix schenckii.

Systemic fungal infections are uncommon
Natural immunity is high physiologic barriers
include 1. Skin and mucus membranes 2. Tissue
temperatureCfungi grow better at less than 37C
(mesophiles) 3. Redox potentialCin vivo
conditions too reducing for most fungi
Infection requires a large inoculum and is
affected by the resistance of the host
  • infection often occurs in endemic areas
  • most infections are asymptomatic or self-limiting
  • in immune-compromised hosts, infections are more
    often fatal (distinction between infection and

Systemic fungal disease is most often associated
with three organisms (in U.S.) 1. Coccidioides
immitis 2. Histoplasma capsulatum 3. Blastomyces
dermatitidis Normally found in soil, these
organisms infect via inhilation.
  • Coccidiodes immitis is considered to be the most
    virulent of fungal pathogens.
  • Restricted to hot, semi-arid areas of SW USA and
  • Grows in the soil, but inhalation of a single
    spore can initiate infection.

In infected tissues, C. immitis appears as a
mixture of hyphae and spherules.
Coccidioidomycosis Normally a benign,
sub-clinical upper respiratory infection
In a small percentage of cases, organism
disseminates from the lungs to a variety of
organs, particularly the CNS, meninges, skin,
soft tissues, and bone
In infected tissues, organism is seen as a
mixture of spherules and endospores.
Risk factors for disseminated coccidioidomycosis
1. Race Filipinos gt African Americangt
Caucasian 2. Age Extremes more
susceptible 3. Sex Males more susceptible 4. Preg
nancy 5. Immunosuppression
1. Suppurative or granulatomas inflammation 2. Sph
erule or endospores seen on pathology 3. Culture
of microorganisms 4. Complement fixation assay
(in cerebrospinal fluid)
Amphotericin B, Fluconazole
  • (also called cave disease)

Caused by the dimorphic fungus Histoplasma
Intracellular yeast at 37C
Tuberculated macroconidia, grown at 25C
Histoplasmosis is characterized by intracellular
growth of the pathogen in macrophages and a
granulomatous reaction in tissue. These
granulomatous foci may reactivate and cause
dissemination of fungi to other tissues.
  • 1. Usually, acute benign respiratory disease
  • 2. Rarely, progressive, chronic or disseminated
  • 3. Endemic area in U.S. -Atlantic Ocean to N.
    Dakota (500,000 cases/year in U.S.), except New
    England Florida. Most cases in Ohio Valley and
    Mississippi Valley)

H. capsulatum grows in soil, especially soil
contaminated by guano (can be cultured from soil).
More Histoplasmosis
90 of histoplasmosis cases are clinically
  • 1. Disseminated histoplasmosis is diagnosed
    frequently in patients with AIDS living in the
    central U.S.
  • 2. It is often the initial manifestation of
  • 3. In these cases, the organism spreads via blood
    from the lung to involve bone marrow, liver,
    spleen, or skin (see calcified granulomas).
  • 4. Spread can also be associated with underlying
    lung disease (e.g., emphysema).

  • Histology and culture
  • Skin test for histoplasmin the major hyphal
    antigen is not useful, because most people are
    positive in endemic area.
  • In HIV-infected patients with disseminated
    histoplasmosis, histo. antigen detection in serum
    and urine is at least 50, and 90 sensitive,

Even More Histoplasmosis
Immune response
  • Cell-mediated responses are of primary importance
  • Phagocytic activity of macrophage is considered
    an important component of resistance to drugs.
  • Activated macrophage can kill yeast

  • Amphotericin still mainstay of therapy vs.
    disseminated histoplasmosis.
  • Ketoconasole or itraconasole is effective as
    therapy for self-limited disease (used in AIDS).

Ocular Histoplasmosis
A small fraction of individuals form scar tissue
in the retina many years after the original
histoplasmosis infection. This scarring can
obscure the macula and lead to loss of central
vision. The first signs are small histo spots.
Advanced disease is treated with laser
photocoagulation to limit the proliferation of
blood vessels.
  • Granulomatous mycotic infection that
    predominantly involves lungs and skin but can
    spread to other organs. Most prevalent in males
    40-60 years of age and children.

Blastomyces dermatitidis
Organism probably originates in the soil (but
cant be cultured from soil in endemic areas) and
infection ensues by inhalation of spores.
  • Most cases are in southern, central, and
    southeastern USA.
  • The pulmonary infection is either self -limited
    or progressive.
  • Dissemination often occurs to the skin and to the
    bone - 80 of patients have large skin lesions a
    large number also have granulomatous pulmonary

  • Clinical findings
  • Direct examination in tissue
  • Isolation (yeast-extract-phosphate agar)
  • Mold to yeast at 37C

  • Amphotericin B is the drug of choice for rapidly
    progressive blastomycosis
  • Ketoconazole for less severe cases

Immune response
1. Alveolar macrophage provide a modest first
line of defense. 2. PMNs (stimulated) also kill
Blastomyces cells (by oxidative
mechanisms). 3. Conidia are more sensitive to
killing by PMNs because yeast are too
big. 4. Cell-mediated immunity of great importance
Opportunistic Mycoses
Opportunistic mycoses are fungal infections that
do not normally cause disease in healthy people,
but do cause disease in people with weakened
immune defenses (immunocompromised people).
Weakened immune function may occur due to
inherited immunodeficiency diseases, drugs that
suppress the immune system (cancer chemotherapy,
corticosteroids, drugs to prevent organ
transplant rejection), radiation therapy,
infections (e.g., HIV), cancer, diabetes,
advanced age and malnutrition. The most common
infections are Candidiasis Aspergillosis Cryptoc
occosis Zygomycosis Pneumocystis carinii
Cryptococcus neoformans
  • Primary infection in lungs
  • Cryptococcal meningitis is most common
    disseminated manifestation
  • Can spread to skin, bone and prostate
  • Organism is ubiquitous and infections occur
  •  C. neoformans recovered in large amounts in
    pigeon poop
  •  Does not cause disease in birds

  • Lumbar puncture and microscopic examination of
    cerebrospinal fluid is diagnostic.
  • (India ink staining)
  • Cyrptococcal antigens in CSF and serum.

Immune response
Phagocytosis by neutrophils is inhibited by the
presence of a capsule. However, activated
neutrophils have an increased capacity to
phagocytize C. neoformans. Cell mediated
immunity primary defense About 30 of
cryptococcus infections occur in patients with
lymphoma (CNS)
Amphotericin B 5FC Fluconazole also effective
  • Genus occurs worldwide and contains hundreds of
  • These species constitute the most commonly found
    fungi in any environment

Major portal of entry is the respiratory tract.
Dissemination can occur from the lungs and
involve other areas of the lung, the brain, GI
tract, and kidney. CNS and nasal-orbital
cavities can also occur without lung involvement.
Risk factors for invasive disease are
neutropenia and high doses of adrenal
  • Aspergillosis is the most common fatal infection
    seen in patients with chronic granulomatous
    disease of childhood. 
  • Patients with this condition are unable to form
    toxic oxygen radicals after phagocytosis. 
  • Progressive and disseminated disease can
    complicate neoplastic diseases, especially acute
    leukemia, bone marrow and organ transplantation
    (not necessarily AIDS).

In immunosuppressed hosts invasive pulmonary
infection, usually with fever, cough, and chest
pain. May disseminate to other organs, including
brain, skin and bone. In immunocompetent hosts
localized pulmonary infection in persons with
underlying lung disease. Also causes allergic
sinusitis and allergic bronchopulmonary disease.
Agent Aspergillus fumigatus, A. flavus.
  • C. albicans is a member of the indigenous
    microbial flora of humans. 
  • 1. Found in the gastrointestinal tract, upper
    respiratory tract, buccal cavity, and vaginal
  • 2. Growth is normally suppressed by other
    microorganisms found in these areas.
  • 3. Alterations of gastrointestinal flora by broad
    spectrum antibiotics or mucosal injury can lead
    to gastrointestinal tract invasion.
  • 4. Skin and mucus membranes are normally an
    effective barrier but damage by introduction of
    catheters or intravascular devices can permit
    Candida to enter the bloodstream.

In vitro (25o C) mostly yeast In vivo (37o C)
Yeast, hyphae and pseudohyphae
  • Vaginal candidiasis is the most common clinical
    infection. Local factors such as pH and glucose
    concentration (under hormonal control) are of
    prime importance in the occurrence of vaginal
    candidiasis. In mouth normal saliva reduces
    adhesion (lactoferrin is also protective).

Immune Response Hyphae are too big for
phagocytosis but are damaged by PMNs and by
extracellular mechanisms (myeloperoxidase and b-
glucuronidase). Cytokine activated lymphocytes
can inhibit growth of C. albicans.  Resistance to
invasive infection by Candida is mediated by
phagocytes, complement and antibody, though
cell-mediated immunity plays a major role.
Patients with defects in phagocytosis function
and myeloperoxidase deficiency are at risk for
disseminated (even fatal) Candidiasis.
Risk factors for candidiasis
Post-operative status Cytotoxic cancer
chemotherapy Antibiotic therapy Burns Drug
abuse Gastrointestinal damage.
Chronic mucocutaneous candidiasis
Chronic mucocutaneous candidiasis (CMC) is the
label given to a group of overlapping syndromes
that have in common a clinical pattern of
persistent, severe, and diffuse cutaneous
candidal infections. These infections affect the
skin, nails and mucous membranes.
Immunologic studies of patients with CMC often
reveal defects related to cell-mediated immunity,
but the defects themselves vary widely.
Mucutaneous candidiasis response to fluconazole
Transfusion of a Candida-specific transfer factor
has been reported to be very successful
(remission for gt 10 years) when combined with
antifungal therapy. The availability of effective
oral agents, especially the azole antimicotics,
has dramatically changed the life of patients
living with CMC.
Environmental species kill neutropenic patients.
  • Zygomycosis. Zygomycosis due to Rhizopus,
    Rhizomucor, Absidia, Mucor species, or other
    members of the class of Zygomycetes, also causes
    invasive sinopulmonary infections. An especially
    life-threatening form of zygomycosis (also known
    as mucormycosis), is known as the rhinocerebral
    syndrome, which occurs in diabetics with
    ketoacidosis. In addition to diabetic
    ketoacidosis, neutropenia and corticosteroids are
    other major risk factors for zygomycosis.
  • Phaeohyphomycosis. Phaeohyphomycosis is an
    infection by brown to black pigmented fungi of
    the cutaneous, superficial, and deep tissues,
    especially brain. These infections are uncommon,
    life-threatening, and occur in various
    immunocompromised states.
  • Hyalohyphomycosis. Hyalohyphomycosis is an
    opportunistic fungal infection caused by any of a
    variety of normally saprophytic fungi with
    hyaline hyphal elements. For example, Fusarium
    spp. infect neutropenic patients to cause
    pneumonia, fungemia, and disseminated infection
    with cutaneous lesions.
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