Opportunistic Fungi

Opportunistic fungi are able to causes disease

in immunocompromised patients.

Opportunistic fungi includes:

a. Candida albicans.

b. Cryptococcus neoformans.

c. Aspergillus fumigatus.

d. Mucor & Rhizopus species.

e. Pneumocystis carinii.

Candida albicans Characteristics:

● Normal flora of mucous membranes of upper respiratory tract, gastrointestinal tract and genital tract.

● Yeast as normal flora, Pseudohyphae and hyphae when invade tissue.

Candida albicans

Transmission: As part of normal flora, no need of transmission.

Clinical findings: Thrush: Over growth of C. albicans occurs in

the mouth and produces white patches. Common in infants, immunocompromised patients.

Vulvovaginitis: Itching and whitish discharge.

Candida albicans

Disseminated infection: Such as

endocarditis, esophagitis, &

endophthalmitis can occur.

Chonic mucocutaneous

candidiasis: Occurs in children

with T- cell defect immunity.

Skin lesion: Warm & moist areas become red and weeping. Fingers and nails of persons employed as dish washers are involved.

mucocutaneous candidiasis

Laboratory diagnosis

Sample: According to the site of lesion. Microscopy: Microscpic examination of tissue

reveals yeast and pseudohyphae. The yeast is gram-positive.

Culture: On sabouraud’s agar media colonies are formed. Germ tube formation and production of chlamydospores distinguish C. albicans from other species of Candida.

Laboratory diagnosis

Germ tube test: Inoculate yeast into

serum Results in germinated

hyphae (within 2 hrs at 37OC for C.albicans)

Specific for C.albicans although C.tropicalis sometimes (rarely) produces germ tubes

Germ tube test

Candida albicans

Colony on SDA

Candida albicans

Mycelium and blastospores

in urine

Vaginal swab

Cryptococcus neofornans Characteristic:

Oval budding yeast.

Have a wide polysaccharide

capsule.

Habitat in the soil containing

bird dropping.

Transmission: by inhalation.

Cryptococcus neofornans

Clinical feature:

Lung infection is often asymptomatic or may ٭ produce flu-like disease or pneumonia.

They spread via blood stream to the ٭ meninges and other system in patients with reduced cell mediated immunity.

.But some cases of meningitis may occur ٭

Laboratory Identification Microscopy: Visualization of encapsulated

yeast in India ink preparation. Gram stain is unreliable but stains such as methenamine-silver, periodic acid-Schiff will allow the organism to be visualized.

Culture: On sabouraud’s agar produces colonies of yeast.

Serlogy: Capsular polysaccharide antigen can be detected by latex-agglutination test.

Cryptococcus neoformans

Colonies on SDA CSF, India ink, capsule

India ink, phase contrastLung section, ecapsulated cells

Aspergillus

Common species: A. fumigatus, A. flavus, A.

niger.

Medical importance: Aspergillus species

especially, A. fumigatus cause infections of skin,

ears, eyes, “fungus ball” in the lungs.

Aspergillus Transmission: Inhalation of airborne spores. Clinical feature: Can colonize and invade

abraded skin, wound, burn, cornea, ear and paranasal sinuses.

In immunocompromised persons invade blood vessels causing thrombosis and infarction.

A person with lung cavity e.g; from tuberculosis may develop a fungal ball.

Laboratory Identification Microscopy: Biopsy specimen shows septate,

branching hyphae. Culture: On sabouraud’s agar produces colonies with

characteristic radiating chains of conidia from central stalk.

Colony on SDA Hyphae in lung section

Aspergillus

Detection of antibody: Patients with allergic

bronchopulmonary aspergillosis have high titer

of specific IgE antibody.

Detection of antigen: Patients with invasive

aspergillosis, their may be high titer of

galactomannan antigen.

Pneumocystis carinii

Trophozoite and cyst forms, therefore thought to be a protozoan

Responds to protozoan drugs, not to fungal drugs

But now classified as a fungus (by rRNA sequencing)

Pneumonia-like disease, especially in immunocompromised

Common killer in AIDS