Systemic mycosis (1) Aspergillosis

Mrs. Dalia Kamal Eldien

Msc in MicrobiologyLecture No-10-

Objectives

Classification of systemic fungal infection Introduction to AspergillosisCommon species of AspergillusPathogenicity of AspergillosisMycology of AspergillusLaboratory diagnosis

Classification of systemic fungal infection

Systemic fungal infections: are often classified as opportunistic or primary.

Opportunistic infections are those that develop mainly in immunocompromised hosts

Examples to opportunistic systemic fungal infections (mycoses) include

Aspergillosis Candidiasis Mucormycosis (zygomycosis) Cryptococosis Geotrichosis

Primary fungal infections: these infections usually result from inhalation of fungal spores, which can cause a localized pneumonia as the primary manifestation of infection. 

Examples to primary fungal infectionsCoccidioidomycosisHistoplasmosisBlastomycosisParacoccidioidomycosis

Introduction

Aspergillosis is a disease caused by Aspergillus speciesAspergillus is a genus of ubiquitous soil fungi, found as

saprophyte in soil, vegetation especially the stored grains,  are common contaminants of starchy foods (such as bread and potatoes), and grow in or on many plants and trees, their spore widely distributed in air, hence they are a very common lab contaminant

all members of the genus Aspergillus likely are members of the Ascomycets, reproduce sexually and asexually giving conidia and ascospore.

Main species

• There are more than 180 species Aspergillus , of which 34 have been associated with human disease, include:

A. fumigatusA. flavusA. terreusA. nigerA. nidulans

Pathogenicity

The clinical manifestations of aspergillosis are determined by the host immune response to Aspergillus spp with the spectrum ranging from a local inappropriate inflammatory response causing allergy, to lung disease with mycelial balls.

In humans, the major forms of disease are:

1- Otomycosis Ear infection

2- Brain abscess Brain infection

3- Mycetoma Subcutaneous tissue infection

4- Endocarditis & myocarditis Heart infection

5- Sinuses aspergillosis Nasal sinuses infection

6- Aspergillus flavus produces the carcinogenic mycotoxin aflatoxin which often contaminates foods such as peanuts.

7- Pulmonary aspergillosis lung infection, have 3 forms: Allergic bronchopulmonary aspergillosis, which affects

patients with respiratory diseases such as asthma, cystic fibrosis, and sinusitis

Acute invasive aspergillosis, a form that grows into surrounding tissue, more common in those with weakened immune systems such as AIDS or chemotherapy patients

Disseminated invasive aspergillosis, an infection spread widely through the body

Mycology of Aspergillus

all members of the genus Aspergillus likely are members of the Ascomycets, reproduce sexually and asexually giving conidia and ascospore.

Vegetative mycelium consisting of septate branching hyphae, colorless.

The conidiophores originate from the basal foot cell located on the supporting hyphae and terminate in a vesicle at the apex.

Vesicle is the typical formation for the genus Aspergillus. The morphology and color of the conidiophore vary from

one species to another. Covering the surface of the vesicle entirely ("radiate"

head) or partially only at the upper surface ("columnar" head) are the flask-shaped phialides which are either uniseriate and attached to the vesicle directly or are biseriate and attached to the vesicle via a supporting cell, metula.

Over the phialides are the round conidia (2-5 µm in diameter) forming radial chains.

The typical Aspergillus head showing a conidiophore, swollen vesicle, phialides, and radiating chains of conidia is formed in cultures and is not often seen in direct specimen except the ear swab.

In the tissue Aspergillus present as branching hyphae named as dichotomous branching hyphae (45C)

Aspergillus head

Aspergillus head

Aspergillus head of different species

species conidiophores vesicle Strigmata(Phialides)

Arrangement of conidiophores

A fumigatus Color lesssmooth

Flask One raw columnar

A. flavus Color lessrough

oval One or two radiation

A. terreus Color lesssmooth

round Two raw Long columnar

A. niger Yellow or brownsmooth

round One or two irregular

A. nidulans variablesmooth

round Two raw Short columnar

Laboratory diagnosis

• Specimens :according to the site of the infection in which fungi are

possible to be the etiological agents .• Direct microscopy:a wet mount preparation of 20% potassium hydroxide, which

aids in the visualization of hyphal elementsFluorescent techniques• Fluorescent dyes—eg, Calcofluor white, U vitex 2B, and

Blankophor, are water soluble, color less dyes that selectively bind to beta-glycosidically linked polysaccharides within fungal cell walls. They are not specific for Aspergillus spp, but have the advantages of relatively high sensitivity.

Tissue sections should be stained with H&E or PAS, Aspergillus hyphae may be missed in H&E stained sections. Examine specimens for broad segmented hyphae showing the dichotomously branched(45C angle).

Direct immunofluorescence technique: by specific antisera

• Culture They are rapid growing& non fastidious organism, so can

grow in simple media Aspergillus spp can be recovered on most routine solid and

liquid microbiological media (eg, blood agar, chocolate agar, brain heart infusion broth). Plus the fungal medium eg, Sabouraud dextrose agar with chloramphenicol and without cyclohexamide, incubate at 37C aerobically, if A. fumigatus is suspected incubate another plate at 43C

Aspergillus are fast growing after (2-7 days) as white mycelia, then colored according to the spore color

The inoculation on Czapek dox agar and potato dextrose agar and incubated at 25oC, will encourage the sporulation. 

Aspergillus molds have a powdery texture. However the color of the mold's surface differs from species to another and can be used to identify the type of Aspergillus, the rate of growth can also be used to identify Aspergillus, with most species growing quite quickly, however A.glaucus and A.nidulans grow more slowly.

Colonial morphology A. fumigatus = blue green and some time grey green A. flavus = yellow green A. terreus = cinnamon brown A. niger = black A. nidulans = deep blue green or buff brown, also have

especial structure: Hülle cell(horse shoes)

Hülle cell

A.fumgatous

A. flavus. 

A.nidulanous

A.niger

A.terrus

Serological diagnosis

Agar Gel Immunodiffusion Test: is the passive diffusion of soluble antigens and/or antibodies toward each other leading to their precipitation in a gel matrix

Counter Current Immunoelectrophoresis: is a modification of immunodiffusion in which antigen and antibody move in opposite directions by charge and form precipitates in the area between the cells where they meet in concentrations of optimal proportions.

Agar Gel Immunodiffusion Test

In this method, immuno precipitation occurs when antigen at the cathode is caused to migrate in an electric field through a suitable medium of diffusion against a stream of antibody migrating from the anode because of endosmotic flow.

This is one-dimensional double electroimmuno diffusion in which antibody and antigen are moved towards each other by an applied electric field, because the gel is buffered at a pH between the isoelectric points of the antigen and antibody. The antigen and antibody are placed in separate wells in an Agarose gel plate.

Materials: Agarose, Antigen, Test antiserum, Positive antiserum, Assay Buffer, Electrophoresis apparatus, slides.

Procedure:

1.Prepare 10 ml of 1.0% Agarose

2. Mark the end of a glass slide as +ve anode and -ve cathode.

3.Place the glass slide on a horizontal surface. Pipette and spread 5 ml of agarose onto slide. Allow to solidify for 15 minutes

4. Cut wells of according to the template using gel puncher.

5. Add 10µl of antigen in each of the two wells towards cathode (Negative electrode) and 10µl of positive control antiserum and test antisera in wells towards anode

6. Connect the power

7. Observe for precipitin line between the antigen and antisera wells.

Counter Current Immunoelectrophoresis

Molecular techniques Polymerase chain reaction and other techniques are

highly sensitive and specific