Medical Mycology: Diagnostic and Detection Methods

Morphology

structure

Biochemistry

using certain elements of the fungus to find the fungus

Genetics

using specific genes of the fungus and comparing it to the infection to detect the fungus

Serology

Detecting the antibodies and antigen to find the fungus

Microscopy (positives)

1. First crucial, first line procedure to detect the fungal elements

2. Is rapid, useful, and effective

3. Gives preliminary info: yeast or mold

Microscopy (Negatives)

1. less sensitivity

2. false negatives

3. Limited info on extra morphological features

Culturing (Positives)

1. useful info on structures not seen on specimen (morphological keys)

Culturing (Negatives)

1. Time constraints (2-10 days)

2. Possible contaminations

3. False positives

4. Chance of non-sporulating cultures

Assimilation Tests

1. Use a small strips that has different substrates

2. The fungus will react to them producing products which give off color

3. The color combinations can identify the fungus

Antigen Test

Direct measurement of current disease activity

Latex Agglutination

• Antigen test

• Qualitative

  1. Latex particles are coated with antibodies specific to that fungi

  2. Take samples from the patient

  3. When the fungus’ antigen interacts with the anti-bodies it causes clumping (agglutination)

Lateral Flow Assay

• Antigen test

• Qualitative

• Like a pregnancy test

  1. Apply the patient sample to a strip and on that part of the strip are antibodies-conjugated

  2. Then there is flow direction (capillary action)

  3. As it flows, it will interact with a test line (anti-bodies), causing a color reaction if the antigen is present

  4. Leftover antigen with interact with the test line causing it to light up too

Immunodiffusion Assay

• Antigen test

• Quantative

  1. Add patient serum to the hole

  2. The serum will diffuse out

  3. If it’s positive, it will cause rings to form

     • Thicker rings, mean higher concentration

Antibody Detection (titer)

A measure of how much a sample can be diluted before antibodies cannot be detected

• A fourfold rise in the anti-body titer=positive

ELISA Test (Enzyme-linked immunoabsorbent assay

• Antibody test

• Quantitive and Qualitative

1. Antibodies are spread onto a micro titer plate, and antigen is added

2. Then a labeled antibody is added and will bind to the antigen if present

3. A substrate is added and will cause a color reaction if antigen is present

PCR (Polymerase Chain Reaction)

1. Denaturing~occurs at 95 degrees, separating the strands

2. Annealing~occurs at 55 degrees causing primer to attach to separated strands

3. Extension~occurs at 72 degrees, synthesizing a new strand with the primers

Prevalence of Disease Formula

(Total Disease/total)*100

Sensitivity

Refers to a test’s ability to designate an individual with the disease as positive

High Sensitivity

Fewer false negatives, and less missed diseases

Specificity

The percentage of true negatives out of all subjects who do not have the disease

High Specificity

Less false positives

Sensitivity formula

(True positives)/(True positives+false positives)

Specificity Formula

(True negatives)/(True negatives+False positives)