Fungus Part II

 There are four main fungal infections in
superficial mycoses:
 Tinea versicolor (Pityriasis versicolor) –skin
 Tinea nigra – skin
 Black piedra – hair
 White piedra – hair

 Malassezia furfur.

 7 species of malassezia have been identified out
of which M.furfur is the commonest.

 Lipophilic fungus found in areas of body rich in
sebaceous glands.

 Macroscopy – dry chalky appearance.

 Microscopy – bottle shaped budding yeast cells.
Spaghetti and meat balls appearance.

: TINEA NIGRA
 Superficial asymptomatic skin disease characterised by
light brown to black macular areas affecting thickly
keratinised regions of palmar and plantar stratum
corneum.

 Exophila wernikii.

 For microscopy KOH mount is done and fur culture
sabouraud’s agar is used.

 White and black piedra:

 Nodules are formed on hair shaft.

 White piedra - tricosporon bigelli.
 Characterised by white nodules on hair shaft of
axilla.

 Blackpiedra - piedraia hortae.
 Characterised by black nodules on hair shaft of
beard and scalp.

 They are fungal infections of skin, hair and nails which
are generally restricted to keratinised layers of skin and
its appendages.

 Dermatophytoses is also called tinea or ringworm.

 As the lesions are often circular, they are called
ringworm.

 The term tinea (latin=worm) describes the serpentine
and annular (ring like) lesions that resemble a worm
burrowing at the margin.

 Hyphae and arthrospores of dermatophytes are present in
lesions while in cultures they appear as septate hyphae
and asexual spores.
 Three genera are differentiated based mainly on the
nature of macroconidia.

 Genus Macroconidia

 Epidermophyton club shaped
 Microsporum spindle shaped
 Trichophyton pencil shaped

 Examples of dermatophytes: T.rubrum, T.tonsurans,
T.mentagrophytes, T.violaceum, M.audouinii, E.flucossum.

 Endothrix: arthrospore formed within hair shaft resulting in
break off of hair. Eg T.violaceum, T.tonsurans.
 Ectothrix: arthrospore formed outside the hair eg.
M.audouinii.
 Favus: T.schonleinii causes favus. Fungal activity is minimal
in hair shaft but intense growth occurs within and around
follicle. This produces characteristic honey comb appearance
on scalp.

 Genus target site
 Epidermophyton skin and nails
 Microsporum skin and hair
 Trichophyton skin, hair and nails

 Classification of dermatophytes based on habitat:
 Anthrophilic dermatophytes
 Zoophilic dermatophytes
 Geophilic dermatophytes

 Classification of ringworm based on site:

 Tinea capitis = ringworm of scalp

 Tinea corporis = ringworm of non hairy skin of body

 Tinea cruris = ringworm of groin, perineum

 Tinea barbae = (barber’s itch) bearded areas of face

 Tinea pedis = (athletic foot) toe clefts

 Nail samples: must include clippings from any
discoloured, dystrophic or brittle parts of nail and
scraped material from underneath the nail preferably
from its edges.

 Scales from skin lesions: using blunt scalpel, the skin
lesion is scraped outward from the edges of the lesions
where most viable fungus is likely to be present.
Specimens from scalp must include hair stubs, contents
of plugged follicles and skin scales.

 Infected hair: are plucked from scalp using forceps. Cut
hair are not suitable as the infection is most likely near
the scalp area of hair.

 Hair brush sampling technique: sample may be
collected from scalp by brushing with a sterilized plastic
hair brush or scalp massage pad which is then
inoculated into culture medium by pressing the brush or
pad spines into sabouraud’s agar.

 Microscopy: KOH mount
 Culture: Sabouraud’s dextrose agar.
 Identification: is done by studying microscopic and
macroscopic features.

 Three genera are recognised:

 Epidermophyton:
 Smooth thin-walled Macroconidia only present, no
microconidia, colonies a green-brown to khaki colour.

 Microsporum:
 Macroconidia with rough walls present, microconidia
may also be present.

 Trichophyton:
 Microconidia present, smooth-walled macroconidia may
or may not be present.

 Causative fungi:

 Cryptococcus neoformans
 Histoplasma capsulatum
 Blastomyces dermatitidis
 Coccidioides immitis
 Paracoccidioides brasiliences

 Cryptococcus is a yeast and occurs worldwide.
The other four are dimorphic fungi infrequently
found in India.

 Infection of systemic fungi is acquired via lungs
by inhalation and primary focus of infection is
lungs.

 The disease is asymptomatic in most cases, but
severe in immunocompromised. Reactivation of
latent infection is possible.

 Definition: It is a subacute or chronic infection caused
by capsulated yeast cryptococcus neoformans.

 Reservoir: cryptococcus is a ubiquotous saprophyte
often found in bird droppings, esp. of wild birds
(pigeon, chicken) and soil.

 Occurrence of infection: throughout world, more in I/C
eg AIDS.

 Morphology: spherical budding yeast cell having
prominent polysaccharide capsule. 4 serotypes are
known – A,B,C and D.

 Virulence factors: antiphagocytic polysaccharide
capsule, melanin produced by cells.

 Route of infection: usually inhalation, esp. of dust
containing excreta of pigeons.

 Clinical features: primary and symptomless granuloma
of lung, cryptococcal meningitis, skin and other
infections, lung infections.

 Laboratory diagnosis:
 Specimen: CSF, biopsy, urine.

 Microscopy: Indian ink preparation shows capsulated
yeast cells.

 Culture: sabouraud’s dextrose agar shows creamy white
mucoid colonies.

 Urease test: +ve

 Carbohydrate assimilation test
 Direct immunofluorescence test
 Latex agglutination test for antigen detection.

 Causative organism: histoplasma capsulatum

 Target site: Reticuloendothelial system

 Reservoir: soil, bird and bat droppings.

 Route of infection: inhalation of spores

 Clinical features: acute pulmonary
histoplasmosis, chronic pulmonary disease,
disseminated disease, ocular histoplasmosis.

 Specimen: sputum, biopsy

 Microscopy: KOH mount, giemsa stain, wright stain.

 Culture: sabouraud’s dextrose agar, brain heart infusion
agar.

 Findings: white cottony mycelium, macroconidia,
microconidia.

 Histoplasmin skin test
 CFT, latex agglutination tests, precipitation tests,
histopathology.

 Causative organism: blastomyces dermatitidis

 Reservoir: soil containing organic debris eg animal
droppings, rotting wood and plant material.

 Route of infection: inhalation of conidia

 Persons at risk: persons collecting firewood or working
in tearing of old buildings.

 Clinical disease: primary pulmonary disease, chronic
cutaneous blastomycoses, disseminated disease.

 Laboratory diagnosis: KOH mount, giemsa stain, PAS
stain, H&E stain, sabouraud dextrose agar, antigen
detection tests.

 Causative organism: coccidioides immitis

 Reservoir: desert soil, rodent burrows, archeological
structures


 Persons at risk: agricultural workers

 Clinical disease: primary pulmonary disease, meningitis,
skin and soft tissue infections.

 Laboratorydiagnosis:
 Specimen = sputum, biopsy, pus etc.

 Microscopy
= spherules and endospores in
KOH mount are pathognomonic.

 Culture = sabouraud’ dextrose agar

 Serology, histopathology, skin tests.

 Causative organism: paracoccidioides braziliensis


 Reservoir: soil with high humidity

 Clinical disease: pulmonary infection, mouth, nose,
lymph nodes, skin, adrenal gland, GI tract etc.


 Specimen: sputum, crusts, pus, biopsy


 Culture: sabouraud’s dextrose agar

 CFT, immunodiffusion tests

 Introduction:
 Some saprophytic fungi of environment that usually do
not produce disease may cause infection under special
conditions such as in immunologically compromised
patients and in terminal stages of chronic disease.

 As these fungi take advantage of the debilitated state
of the individual to become pathogenic, they are
referred to as opportunistic fungi.

 The incidence of these fungal infections has increased
in AIDS and with wide use of antibiotic, steroids, and
immunosuppressive drugs.

 Yeast: cryptococcus
 Yeast like fungi: candida, torulopsis
 Filamentous fungi:
 Aspergillus
 Mucor
 Rhizopus
 Absidia
 Cephalosporium
 Fusarium
 Penicillium
 Geotrichum
 Others: pneumocystis carinii

 Candidiasis is a major disease problem in
immucocompromised patients in AIDS and after
prolonged antibiotic therapy and invasive
surgery.
 Medically important species:
 C.albicans,
 C.stellatoidea,
 C tropicalis,
 C.krusei,
 C.gullermondii
 C.viswanathii
 C.glabrata
 C.parapsilosis

 Morphology: spherical or oval budding yeast cells,
pseudohyphae, pseudomycelium, blastospores.

 Commensalism: candida occur as commensals in human
body at sites like intestine, oral cavity, vagina, rectal
area.

 Mode of infection: endogenous or exogenous

 Predisposing factors: DM, immunodeficiency including
AIDS and malignancy.

 Lesions:

 Mucous membrane: oral thrush, vaginal thrush. These
are white patches on the mucosal surface.
 Skin: moist areas of skin like axilla, groin, perineum,
submammary folds, toe clefts etc are affected
commonly.
 Nails: infection of finger webs, nail folds, nails. Occurs
as reddened swelling. ASSOCIATED WITH FREQUENT
IMMERSION OF HANDS AND FEET IN WATER.
 Chronic mucocutaneous candidiasis
 Systemic candidosis: endocarditis, organs like lungs
kidneys etc affected.


 Microscopy: KOH mount, gram stain
 Culture: sabouraud’ dextrose agar shows creamy white
smooth colonies with yeasty odour.

 Germ tube test: candida albicans grown in human serum
at 37 C for 3 hours when examined in KOH shows
filamentous outgrowths (germ tubes).
 Chlamydospores develop in nutritionally poor medium
like corn meal agar at 28 C.

 Serological tests
 Skin tests

 Introduction: worldwide distribution
 Spores are very commonly seen in soil,
food, paint, air vents, disinfectants even.
 Main species:
 A.fumigatus
 A.flavus
 A.niger
 A.terreus
 A.nidulans
 A.glaucus

 Aspergillus asthma

 Bronchopulmonary aspergillosis

 Aspergilloma = often called fungus ball in which
fungus colonises in preexisting cavities (often
tuberculous, sometimes bronchiectatic)

 Disseminated aspergillosis
 Superficial infections

shows septate mycelium
with characteristic
dichotomous branching
 Culture: SDA shows
velvetty powdery
colonies.
 Skin tests
 serology

 P.carinii is a unicellular eukaryotic organism with
tropism for growth on respiratory surface of
mammals.

 Originally classified as a protozoan, it is now
thought to resemble more to fungus.

 Transmission: droplet inhalation, close contact

 Morphology: giemsa stain, methanamine silver stain are
useful.
 Trophic form (trophozoite) 1.5-4 µm D
 Cystic form (sporocyst) 4-7 µm D
 Mature spore case is about 5 µm D containing 8
spherical oval to fusiform spores (1-3 µm D).

 Clinical features:
 In immunocompetent patients the infection is
asymptomatic
 In immunocompromised patients it causes INTESTITIAL
PNEUMONIA.
 It may also cause extrapulmonary manifestations.

 Specimen: aspirates of bronchial washings and
sputum, percutaneous transthoracic needle
aspiration, bronchoalveolar lavage.

 Microscopy:giemsa stain shows purple nuclei,
cytoplasm light blue, cell wall as clear
unstained area. Gomori methenamine stain
shows cyst wall.

 Culture:
NOT CULTIVABLE
 Immunofluorescence study.

Fungus Part II

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Fungus Part II