Week 9 Flashcards
Sporotrichosis
Granuloma ulcer at a skin puncture e.g. from a thorn prick, may produce secondary lesions along draining lymphatics is normally self-limiting but may exist in chronic form
Treated with oral itraconazole
What causes sporotrichosis?
Sporothrix schenckii
* Fungus found in soil, on plant material
* Dimorphic fungus: Mould in the environment (ambient temp) and yeast during human infection (37°C)
How do we diagnose sporotrichosis?
- Biopsy of infected area
- Culture on Sabourauds agar
- Microscopy
Histoplasmosis
Infection results after inhalation of the conidia
Majority of cases are subclinical, or completely benign
Minority of cases develop a chronic progressive lung disease, a chronic systemic disease or an acute fulminating fatal systemic disease (more common in children)
Diagnosis by X-ray (areas of pulmonary calcification),
histoplasmin skin test, or culture
Ocular histoplasmosis syndrome
Spores may spread from lungs to the eye lodging in a layer of blood vessels called the choroid
Abnormal blood vessels form lesions, which can turn into scar tissue in the
central part of the retina (yellow
discolouration seen on the eye)
Scar tissue formation results in vision loss
Histoplasma capsulatum
Dimorphic pathogen i.e.
At room temperature it takes on a mycelial (filamentous) form forming macroconidia and microconidia
At human body temperature, it converts into a yeast form
Treatment for histoplasmosis
Amphotericin B binds to ergosterol in the cell membrane
Intraconazole inhibits enzymes involved in the biosynthesis of ergosterol
Aspergillus
filamentous, thermally monomorphic, saprophytic moulds
wide spread in environment (colonise grain, leaves, soil, living plants)
conidia easily dispersed into environment, humans became
usually infected by inhaling them
among the most frequently encountered organisms in clinical laboratory
Aspergillosis
Aspergillosis
* Pneumonia
* Septicaemia
* Multi-organ disease
Treated with voriconazole OR
amphotericin B
What causes aspergillosis?
– Aspergillus fumigatus and other
Aspergillus species
– A filamentous mould
How does one get aspergillosis?
Aspergilli are found in organic debris
* Dust, soil
Immunosuppressed people
* Inhale or ingest fungal spores
How does one diagnose aspergillosis?
– Chest X-ray
– Sputum culture
– Blood culture
– Serology based on galactomannan which is a component of the Aspergillus cell wall
– Macroscopic (colony)
morphology after culture on
Sabourauds agar at 37°C
– Microscopic morphology
Clinical significance Aspergillosis
incidence of infection relatively rare (high degree of natural
resistance in healthy host)
particular predilection to invade blood vessels, causing
thrombosis and haemorrhagic infarction
Aspergillosis
− invasive lung infection, pulmonary fungus ball (fungus
colony grows within congenital or inflammatory lung cyst)
− allergic bronchopulmonary aspergillosis
− external otomycosis, mycotic keratitis, sinusitis
− endocarditis, central nervous system infections
− onychomycosis, disseminated infections
Aflatoxins
− powerful secondary metabolites produced by growth of
Aspergillus flavus complex
− toxic, cause aflatoxicosis after consumption of affected
foodstuff
− carcinogenic, strong evidence for causal role in primary hepatocarcinoma
Specimens Aspergillus
biopsy material
transtracheal aspirates, sputum
skin scrapings, infected nails
significance of isolation
− detection in specimen of hyphal elements compatible with morphology of isolated mould
− isolation of several colonies of fungus or repeat isolation of same fungus from multiple specimens from patients having compatible clinical picture
Direct examination Aspergillus
in acute invasive infection:
− hyaline, closely septate hyphae, 3µm to 6µm in diameter
− branch dichotomously at acute (45o) angles
− have smooth parallel walls with no or slight constriction at septa
in chronic infection:
− short, distorted hyphae may be wide 12µm
when hyphal elements typical of aspergilli present,
presumptive diagnosis can be made
must be confirmed by culture or immunologic techniques
Aspergillus Isolation and identification
most species of Aspergillus are susceptible to cycloheximide (media containing this compound should not be used)
Growth in culture
− septate, hyaline, branched hyphae give rise to upright conidiophores terminating in swollen cell - vesicle
− conidiophore varies in colour, length, wall ornamentation in different species; usually aseptate
− conidiophore arises either directly from vegetative hyphae or from specialised hyphal cell - foot cell
− vesicle: globose, subglobose, hemispherical, or pyriform (pear
shaped)
− vesicle or a portion of it covered with phialides, which form conidia
Growth temperature studies
− Aspergillus fumigatus complex can grow up to 50oC
− other species are less thermotolerant
Exoantigen tests
− useful for rapid identification to genus level
MALDI-TOF MS-based systems
Characteristics of Aspergillus species
Growth rate
− usually rapid, mature within 3 days
− some species slower growing
Colony morphology
− surface at first white, later turns yellow, green, brown, or black depending on species
− texture velvety or cottony
− reverse white, yellow, or brown
Microscopic morphology
− morphology of conidia / spores, spore bearing structures, type of hyphae
Immunodiagnosis Aspergillus
serologic tests which detect circulating antibodies:
− Enzyme-linked immunosorbent assay (ELISA) - highly
sensitive
− Indirect immunofluorescence - highly sensitive
− Agar gel immunodiffusion (ID)
detects presence of precipitins to various antigen
preparations of Aspergillus spp.
lacks sensitivity
gives no quantitative information on antibody
concentrations
tests which detect soluble antigens of Aspergillus spp. (e.g., galactomannan) in serum, urine, or other body fluids:
− ELISA
− Immunoblotting
Therapy aspergillosis
Allergic forms of aspergillosis
− corticosteroids and antifungal agents
Aspergilloma
− treatment varies considerably with its severity
asymptomatic patients may not need treatment
other patients may require surgical resection
− both amphotericin B and flucytosine recommended
Local, superficial aspergillosis
− nystatin
Invasive aspergillosis
− aggressive treatment with amphotericin B initiated as soon as possible
Yeasts of medical importance
species of unicellular fungi capable of producing diseases of humans and animals
ubiquitous in environment
found on fruits, vegetables, other plant materials - exogenous
normal flora in and on human and animal bodies - endogenous
most common fungi isolated from human patients
considered opportunistic pathogens
may be cultured from specimens of patients immunocompromised
Candida Natural habitat
− part of normal flora of skin, mucous membranes,
gastrointestinal tract
− potential pathogens
− present in clinical specimens as result of: environmental contamination, colonisation, actual disease processes
Candida albicans
Virulence factors
− adherence to epithelial cell membranes
germ-tubes more adhesive than yeast cells
− protease(s)
enzyme(s) capable of digesting host immunoglobulins and other substrates
Dimorphism
− budding yeast cells (produced when part of normal flora)
− pseudohyphae
− true hyphae (produced only during tissue invasion)
candidiasis Clinical significance (Candida albicans)
candidiasis occurs world-wide
most common cause of systemic mycosis
− physiologic (pregnancy, old age, infancy)
− traumatic (maceration, burns, other infection)
− haematological (leukaemia, lymphoma)
− endocrine (diabetes mellitus, hypoparathyroidism, iron
metabolic disorders)
− iatrogenic (antibacterial antibiotics, steroid treatment)
− other (AIDS)
candidiasis grouped into 3 categories:
− Cutaneous and mucosal
e.g., oral thrush, stomatitis, oesophagitis, intertriginous candidiasis, onychomycosis, vaginal thrush, balanitis can be caused by conditions that result in chronic
maceration of these areas
− Systemic
follow introduction of Candida species into bloodstream
e.g., meningitis, endophtalmitis, myocarditis,
endocarditis, bronchopulmonary candidiasis, intestinitis, infant diarrhoea, pyelonephritis, cystitis, osteomyelitis, arthritis
− Chronic mucocutaneous
infection of any or all of epithelial surfaces of body (skin, oral mucosa, upper respiratory tract, gastrointestinal, urinary, genital epithelium)
invasion of bloodstream or deeper tissues unusual
allergic reactions to Candida antigens may occur
Candida albicans Isolation and identification
Germ-Tube Test
− simplest, most valuable test for rapid presumptive
identification
− not all isolates of Candida albicans germ-tube “+” (5%
isolates “-”)
− some isolates of Candida tropicalis may rarely produce
germ-tubes
− Candida albicans blastoconidia smaller, no constricturewhere hyphal initial (germ-tube) joins blastoconidia
− Candida tropicalis blastoconidia larger, constricture where hyphal initial joins blastoconidia
Cornmeal agar morphology (Dalmau plate technique)
− polysorbate (Tween) 80 added to reduce surface tension to promote germination and sporulation of yeasts
− certain species of yeasts develop characteristic
morphological features
− Candida albicans produces:
chlamydospores
clusters of blastoconidia arranged at regular intervals along pseudohyphae
