Characteristics of Fungi

Non-motile eukaryotes lacking chlorophyll
– Contain nucleus, mitochondria, 80S ribosomes
– Cell wall is composed of polysaccharides ,
polypeptides and chitin and the cell membrane
contains sterol which prevent many antibacterial
antibiotics being effective against fungi.
– Larger than bacteria
– Relatively simple nutritional requirements, wide range
of growth rates
• Form visible colonies in days to weeks

Unicellular or multicellular depending on the
species

Fungi can be divided into: Yeast, Mould
(filamentous fungi) and Dimporphic fungi
1
Molds


Multicellular, tubular structures (hyphae)
Hyphae can be septate (regular crosswalls) or
nonseptate (coenocytic) depending on the species
(grow by apical extension)
– Vegetative hyphae grow on or in media (absorb nutrients);
form seen in tissue, few distinguishing features
– Aerial hyphae contain structures for production of spores
(asexual propagules); usually only seen in culture
2
Molds - identification

Identification based on colony morphology
(pigment, texture) and morphology of
reproductive structures
– Conidia - spores formed by budding (blastoconidia) or
disarticulation of existing hypha (arthroconidia)
– Sporangiospores - produced by free-cell formation within
sporangium in nonseptate molds
1
1.
2.
3.
4.
5.
Conidiopspores
Phialides
Vesicle
Conidiophore
Septate hyphae
1
3
2
3
4
2
5
5
1.
2.
3.
4.
sporangium
sporangiophore
Endospores
Nonseptate
hyphae
5. rhizoids
4
3
Colonial Morphology of Fungi
Cryptococcus
Trichophyton
Wangiella
neoformans
tonsurans
dermatitidis
Candida
T. mentaAspergillus
albicans
grophytes
fumigatus
4
Yeasts

Unicellular, 3-5 µm, reproduce by budding
(blastoconidia formation) or fission
 Identified by microscopic morphology (grow
on cornmeal agar) and biochemical tests
(sugar assimilation, enzymatic activity).
 Molds and yeast are not exclusive forms,
some species may exist in both yeast and
mold forms (dimorphism).
5
Classification of Fungi

Taxonomy is based on structural features of the
teleomorph (sexual phase).
– Zygomycota - includes all fungi with nonseptate hyphae
– Ascomycota - includes most human pathogens
– Basidiomycota - mainly plant pathogens
– Deuteromycota (fungi imperfecti)
6
Isolation of fungi

Direct examination:Wet specimen preparations
– e.g. Aspergillus hyphae in sputum or Cryptococcus
neoformans in CSF (mixed with india ink)
– Potassium hydroxide (KOH) cleared specimens , e.g.
dermatophyes (ringworm fungi) in skin scrapings, nails or
hair
– Stained preparation: e.g. Candida albicans in Gram
stained smears of vaginal discharge or pneumocystis
carinii in Giemsa or other stained preparations of bronchoalveolar lavage or sputum.
7
Isolation of fungi

Culture Media
– General purpose media
• BHI + blood, inhibitory mold agar
• Sabouraud dextrose agar
– Mycosel
• Sabouraud + chloramphenicol and cycloheximide
• For isolation of dermatophytes (some pathogenic
fungi are inhibited by cycloheximide)

Incubation
– 30°C for 30 days
8
Medically important fungi

Molds
•
•
•
•
•

Dermatophyte
Fungi causing mycetoma ‫داء القدم الفطري‬
Fungi causing chromomycosis ‫فطر ملون‬
Aspergillus species
Zygomycetes: Mucor ‫عفن فطري‬
Yeast
• Candida albicans
• Cryptococcus neoformans
• Malassezia furfur

Dimorphic
•
•
•
•
Histoplasma species
Blastomyces dermatitidis
Paracoccidioides brasiliensis
Coccidioides immitis
9
Fungal Infections

Fungi generally have low pathogenic potential
– Only a few true pathogens; many opportunists
– Most are acquired from exog/environ sources
– Pathology caused by tissue invasion and/or host
inflammatory response. Many fungal infections can
be characterized by extent of invasion
Type of infection
superficial
cutaneous
subcutaneous
deep/systemic
opportunistic
Example
Malasezzia furfur
dermatophytes
sporotrichosis
histoplasmosis
candidiasis
10
Dermatophytes

Fungi that cause superficial/cutaneous infections
– Confined to keratinized tissue (hair, skin, nails)
– Cause of ringworm (eg tinea capitis, tinea pedis); inflammation
greatest at advancing edge.
– All are molds. Many species produce macroconidia
• Epidermophyton (2 spp), Microsporum (16 spp), Trichophyton
(24 spp)
– Transmitted indirectly via desquamated skin and hair (combs
‫ االمشاط‬hats ‫قبعه‬, showers, etc).

Diagnosis based on direct exam
of scrapings,
culture on selective media.
M. canis
11
Subcutaneous Mycoses

Caused by direct inoculation of organisms from
soil or decaying plants
– Generally cause localized infection
– Hands and feet are most common sites

Sporotrichosis ‫داء الشعيرات المبوغة‬
– Caused by dimorphic fungus Sporothrix schenkii
• Mold in environment, yeast in infected tissue
– Commonly affects hands  trauma from thorns
‫(شوكه‬eg rose gardens); causes lympho-cutaneous
infection
• Extracutaneous (pulmonary) and disseminated
disease uncommon
12
Subcutaneous Mycoses (continued)

Chromoblastomycosis‫الفطر البرعمي الملون‬
– Slow, progressive, granulomatous
infection.
– Skin lesions contain dark brown
sclerotic bodies.
– Caused by dematiaceous (black)
molds, eg Cladosporium, Phialophora.

Mycetoma
– Swollen lesion, granules (containing organisms)
draining from sinuses.
– Can be caused by fungi eg Pseudoallescheria or
actinomycetes (prokaryotes)
13
Candidiasis

Genus Candida - diverse group of yeasts
– Budding yeast, stain Gram-positive
– ID based on biochemical tests and morphology (corn
meal agar)

C. albicans - most important pathogen
– Multiple forms: budding yeast, pseudohyphae, true
hyphae. Forms germ tubes (in presence of serum).
14
Pathogenesis of Candida infections

Most infections are endogenous
– Candida is component of normal oral, GI, vaginal flora

Pathogenic factors
– Essential role of mucosal adherence
– Alterations in micro-environment and/or microbial
flora predispose to symptomatic infection.
– Germ tube formation, proteinases, phospholipases
may contribute to local invasion by C. albicans
15
Candida infections

Cutaneous infections - nails, diaper rash,

Mucosal infections
– thrush (tongue, oral mucosa), pseudo-membrane;
seen with inhaled steroids, cancer, HIV
– esophagitis in suppressed pts (mucosal invasion)
– vulvovaginitis (discharge containing epithelial cells,
pseudohyphae, hyphae)
16
Candida infections

Candidemia/disseminated candidiasis
– Candida spp are 4th leading cause of
nosocomial bloodstream infections
– Antibiotics, iv catheters increase risk
• Antibiotics eliminate normal GI flora, permit
overgrowth of Candida and entry across
damaged mucosa
• IVs provide entry through skin
– Dissemination to kidney, brain, myocardium, eye
is common.
• Ocular candidiasis - white cotton ball-like
lesions of retina; can cause blindness
17
Candida infections (continued)

Urinary tract candidiasis
– Usually seen in pts with urinary catheter.

Hepatosplenic candidiasis
– Occurs in severely compromised (neutropenic)
pts. Multifocal abscesses
18
Candidiasis - Diagnosis

Direct microscopic examination
– Important to demonstrate tissue invasion in
mucosal infection; positive culture alone may be
due to colonization

Culture
– Candida spp grow well on standard media.
– Candidemia readily detected with commercial
blood culture systems.
19
Cryptococcus neoformans

Encapsulated yeast
– Identification based on presence of capsule, urease,
growth at 37°C, melanin synthesis, and sugar
assimilation.

Major virulence factors
– Polysaccharide capsule
• Antiphagocytic
• Immunosuppressive
– Melanin synthesis
20
C. neoformans - Clinical features

Acquired by inhalation
– Most infections are asymptomatic. May present as
isolated pulmonary nodule (r/o carcinoma)

Cryptococcal meningitis
– Dissemination from lung. Life-threatening
– Major opportunistic infection in HIV pts with low CD4
counts
21
Cryptococcocal meningitis

Diagnosis
– CSF WBC count may not be elevated
• Poor prognostic sign
– Direct detection of capsular antigen in CSF
• Latex agglutination or EIA
• High sensitivity and specificity; has displaced
India ink (lacks sensitivity)
– Culture - gold standard

Treatment
– Amphotericin B + 5-fluorocytosine
– In HIV patients, C. neoformans cannot be
eradicated, requires suppressive therapy.
22
Histoplasma capsulatum - Dimorphism

Filamentous mold in environment
– Thin septate hyphae, microconidia, and tuberculate
macroconidia (8-14 µm)

Budding yeast (2-4 µm) in tissue
– Dimorphic transition is thermally dependent and
reversible (25°C  37°C).
Hyphae, micro- and macroconidia
Yeast within histiocyte
23
H. capsulatum - Epidemiology
– H. capsulatum can be cultured from soil in endemic
areas. Abundant growth in soil containing bird feces
(starling roosts, chicken houses) or bat guano
(caves).
24
H. capsulatum - Pathogenesis

Conidia or hyphal fragments are inhaled,
ingested by macrophages.
 Organisms convert to yeast phase,
proliferate in nonimmune macrophages, and
spread through RES.
 Dissemination is common and occurs early,
but is usually asymptomatic.
 CMI response results in macrophage
activation, increased fungicidal activity.
Infection is contained but not necessarily
eradicated.
25
Histoplasmosis - Self-limited Syndromes

Acute pulmonary histoplasmosis accounts
for most cases of symptomatic infection
– Fever, chills, headache, myalgia, anorexia,
nonproductive cough, pleuritic chest pain.
– Enlarged lymph nodes, patchy infiltrates.
– Patients usually improve in several weeks.

5-10% symptomatic cases develop
inflammatory syndromes (arthritis, erythema
nodosum, or pericarditis)
26
Chronic pulmonary histoplasmosis

Slowly progressive pulmonary disease.
 Usually associated with preexisting lung
disease.
– Cough, dyspnea, chest pain, fatigue, fever, night
sweats, and weight loss

Usually progresses if untreated
– AmB or itraconazole (depending on disease
severity) reduces symptoms, improves
radiographic findings, eliminates H. capsulatum
from sputum
27
H. capsulatum - Culture

Histoplasma produces mycelial growth with
characteristic warty ‫مثل الثألول‬conidia when
cultured at room temperature.
 Small microconidia and characteristic large ,
round , spiny macroconidia are produced.
 At 37 C on certain media it is possible to
induce the yeast phase of this dimorphic
fungus
– Sputum best for pulmonary histoplasmosis
– Bone marrow or blood best for disseminated
histoplasmosis
28
H. capsulatum – Direct examination

Examination of infected tissue
(eg bone marrow, liver, skin, GI
mucosa) can provide rapid
presumptive evidence of
disseminated histoplasmosis

Intracellular yeasts can be seen
on peripheral smears in severe
disseminated disease
NEJM 342:28
29
C. immitis - Dimorphism

Grows as hyphae in environment. Forms thickwalled arthroconidia alternating with thin-walled
cells.

Spherule ‫ كرية‬filled with endospores in infected
tissue.
30
C. immitis - Pathogenesis

Arthroconidia are inhaled and convert to
spherules that grow to 20-150 µm. Partially
resistant to killing by phagocytic cells.

Spherules undergo multiple nuclear divisions
and segmentation of cytoplasm to produce
hundreds of endospores (2-5 µm). The
spherule ruptures, releasing endospores that
form new spherules.
31
C. immitis - Epidemiology
Can be cultured from soil in areas where disease
is endemic. Expected number of infections is
100,000 annually
32
C. immitis - Respiratory Infections

40% of pulmonary infections are symptomatic
– Most are self-limited
– Fatigue, cough, chest pain. May also have fever,
dyspnea, myalgia, and headache

Pulmonary nodules
– 4% of infections give rise to solitary ‫ وحيدة‬nodule ( 5
cm)
– Can form cavities, infreq rupture into pleural space
33
C. immitis - Disseminated infections

Occurs in ~ 0.5% of infections. Increased risk:
– HIV, organ transplants, steroids, Hodgkin’s

Skin is most common site of dissemination
 Joints and Bones
– Prominent synovitis, effusion; knee most common
– Vertebrae (multiple) > long bones
– culture (50%) and histopathology for diagnosis

Meningitis
– Headache, vomiting, alt mental status. WBC
(mono), prot, gluc in CSF. Culture usually neg.
34
C. immitis - Culture and Histopathology

Culture - white fluffy ‫وبري‬mold at 25-30ºC.
– Arthrospores are suggestive but not diagnostic

Histopathology
– Acute inflammation (PMNs and Eos) assoc with
active infection and ruptured spherules
– Granulomas assoc with chronic infection,
unruptured spherules
35
Blastomyces dermatitidis

Microbiology
– Hyphae with microconidia at room temp
– Convert to broad-based budding yeast at
37ºC.
 pulmonary infection (asymptomatic or
pneumonia); chronic pulmonary disease
common
 Disseminated disease: skin (common) and
bones
36
B. dermatitidis - Diagnosis

Culture
– White light tan mold at room temp, not diagnostic
– Identification based on conversion to yeast at 37ºC,

Histopathology
– Thick walled broad based
budding yeast
– suppurative and/or
granulomatous inflammation
37
Paracoccidiodes brasiliensis

Microbiology
– Hyphae at room temp.
– Converts to yeast with
multiple buds at 37ºC.
– Probably acquired by inhalation. Pulmonary
infection can be asymptomatic, acute, or chronic
– Extrapulmonary disease in adults > 30 usually
involves oropharyngeal mucosa and regional
lymph nodes.
38
Penicillium marneffei

Only dimorphic species in genus Penicillium
• Infection probably occurs through inhalation
• Chronic illness, low-grade fever, wt loss, skin
lesions, disseminated infection
– Intracellular forms resemble H. capsulatum;
extracellular forms exhibit septa (cells divide by
fission, not budding)
– Grows as mold at 25-30ºC
• Produces soluble red pigment
• Converts to yeast phase at 37ºC
39
Aspergillus spp.




More than 100 species of Aspergillus. Septate
hyphae branching at 45 angle.
Omnipresent ‫ موجودة بكل مكان‬in environment. A.
fumigatus is thermotolerant (up to 55oC) and is
found in high concentrations in compost ‫اوراق‬
‫الشجر‬sites.
Most human disease caused by A. fumigatus, A.
flavus, and A. niger.
Opportunistic pathogen, airborne spread
40
Aspergillus Infections

Allergic bronchopulmonary aspergillosis
 Aspergilloma (fungus ball)
– Colonization of preexisting lung cavity (TB,
abscess, etc(.

Invasive pulmonary aspergillosis
– Occurs in pts with immunosuppression and
neutropenia.
– Vascular invasion, infarction, cavitation
– Hematogenous dissemination common (ocular,
cerebral, cutaneous involvement)
41
Aspergillosis - Diagnosis

Direct examination
– Difficult to distinguish branching septate hyphae
of Aspergillus spp from other opportunistic fungi,
eg Pseudallescheria, Fusarium.

Culture
– Aspergillus spp grow well on standard media.
Airborne contaminants are a problem.
– Need to see several colonies from one specimen
or same organism in multiple specimens.
42
Mucormycosis

Infections caused by Mucoraceae
– Mucor, Rhizopus, Absidia
– Broad nonseptate hyphae, sporangia.
• Widespread in environment; found in
decaying vegetables and fruits, soil, old
bread; grow and sporulate on materials
containing carbohydrates. R. oryzae is
most common clinical isolate.
43
Mucormycosis - Clinical features

Rhinocerebral/craniofacial mucormycosis
– Infection of paranasal sinuses with extension
from ethmoid into orbit or frontal lobe (also
cavernous sinus thrombosis).
– Prompt diagnosis essential; direct exam of
turbinate scrapings and/or sinus aspirate.

Pneumonia
– Resembles invasive pulmonary aspergillosis

Cutaneous infection
– Associated with localized trauma
– Cellulitis with central necrotic area.
44
Antifungal Drugs

Polyenes (Amphotericin B, nystatin)
 Azoles (fluconazole, itraconazole)
 Echinocandins (caspofungin)
 5-Fluorocytosine
45