Staining of microorganisms Flashcards
What is the primary complaint of the 33-year-old female patient?
Chronic shortness of breath on exertion
The patient has a history of similar symptoms and was previously diagnosed with acute bronchitis.
What significant finding was reported in the CT scan of the patient’s chest?
Diffuse centrilobular micronodular pattern without focal consolidation
This finding is relevant for diagnosing potential pulmonary issues.
What microorganism was identified in the cytology of the bronchoalveolar lavage?
Histoplasma capsulatum
This organism is associated with respiratory infections and is often found in certain environmental conditions.
List the four groups of micro-organisms that are medically important and of interest to histotechnology.
- Bacteria
- Fungi (Yeasts)
- Viruses
- Protozoa
What is the cell wall composition of bacteria?
Composed of peptidoglycan (mucopolysaccharide)
This structure is crucial for bacterial integrity and function.
How are bacteria classified?
- Shape
- Arrangement or formation
- Gram stain reaction (Gram positive vs Gram negative)
- Other stains (e.g., Acid-Fast techniques)
What are the three main shapes of bacteria?
- Cocci
- Bacilli
- Spirochetes
What are the two most common differential staining techniques?
- Gram Stain
- Acid-fast stains
What is the purpose of running control slides when performing a Gram stain?
To ensure the accuracy of the staining technique and tissue sample
Control slides should be known positive for the type of organism being demonstrated.
What is the preferred fixative for Gram staining?
10% neutral buffered formalin
Proper fixation is essential to preserve tissue morphology.
What color do Gram positive and Gram negative organisms appear in a Gram stain?
- Gram positive: blue
- Gram negative: red
What are the differences between Gram positive and Gram negative bacteria?
- Gram positive: thicker cell wall (15-25 nm), more layers of peptidoglycan
- Gram negative: thinner cell wall (8-12 nm), irregular layer of lipoprotein
What is the principle behind the Gram stain procedure?
Differentiates bacteria based on their cell wall properties and porosity
The staining process involves a series of steps that lead to different colors based on bacterial type.
What is the purpose of the Ziehl-Neelsen technique?
To demonstrate acid-fast bacteria in tissue sections
This technique is particularly useful for identifying Mycobacterium species.
What is the chemical that forms a strong union with basic fuchsin in acid-fast staining?
Mycolic acids
These lipids are crucial for the retention of the stain in acid-fast bacteria.
What color do acid-fast bacilli appear in the Ziehl-Neelsen stain?
Red
The background typically stains blue.
What is the Warthin-Starry technique used for?
Demonstration of spirochetes in tissues
This method uses silver staining to visualize these organisms.
What is the role of hydroquinone in the Warthin-Starry technique?
Chemical reducer that allows spirochetes to bind to silver ions
This is part of the argyrophilic staining method.
What are the expected results of the Warthin-Starry technique?
- Spirochetes: black
- Nuclei: brown
- Background: golden yellow
What is the Kinyoun method known for?
It is a cold method for acid-fast staining that uses a more concentrated primary stain
This method does not require heating.
What color do spirochetes stain in the Warthin-Starry technique?
black
In the Warthin-Starry technique, spirochetes are demonstrated as black.
What is the preferred fixative for the Warthin-Starry technique?
10% NBF
Mercurial and chromate fixatives should always be avoided.
What is the principle behind the Warthin-Starry technique?
Argyrophilic organisms are demonstrated by absorbing silver from solution with a reducing agent
The reducing agent used is hydroquinone.
What are the results of the Warthin-Starry technique for Helicobacter pylori?
dark brown/black
Other bacteria also stain dark brown/black.
Which bacterium is responsible for causing Legionaire’s disease?
Legionella pneumophilia
This bacterium is identified in the Warthin-Starry technique.
Fill in the blank: H. pylori infection may be present in more than half the people in the world, but most are _______.
asymptomatic
What is the most reliable method for demonstrating fungi?
Grocott Methenamine Silver Technique
This method is based on the polysaccharide cell wall of fungi.
What are the four classifications of fungi?
- Filamentous (molds)
- Yeasts
- Pseudohyphae
- Dimorphic fungi
What is the purpose of the Grocott Methenamine Silver technique?
For the demonstration of fungus
Which fungi are known to cause opportunistic infections in immunosuppressed patients?
Candida albicans
This is an example of a secondary opportunistic infection.
True or False: Most fungi stain gram negative.
False
Most fungi stain gram positive.
What two dyes are used in the Diff Quik method for detecting H. pylori?
methylene blue and azure A
What is the reducing agent used in the Warthin-Starry technique?
hydroquinone
What color is the background when using the Warthin-Starry technique?
golden yellow
List the steps in the Grocott Methenamine Silver Technique.
- Oxidation
- Silver exposure
- Toning
- Removal of excess silver
- Counterstain
What can cause false positives when staining for spirochetes?
Reducing substances present in the tissue, such as formalin pigment
What is the significance of using a 0.5% silver nitrate solution in the Warthin-Starry technique?
It aids in the demonstration of argyrophilic organisms
Fill in the blank: The Grocott Methenamine Silver technique relies on the _______ reaction.
argentaffin
What is the purpose of counterstaining with light green in the Grocott Methenamine Silver technique?
To stain the background green
What is the role of sodium thiosulphate in the Grocott Methenamine Silver technique?
Fixes reduced silver and binds with unreduced silver
What are some sources of error in the Grocott Methenamine Silver technique?
- Dirty specimen jars
- Contaminated water
- Rubber tubing
- Paraffin wax
What does the Genta stain visualize in addition to H. pylori?
Inflammatory cells
It combines silver, H&E, and Alcian blue stains.
What color do fungi stain in the Grocott Methenamine Silver technique?
black
What is the significance of treating sections with sodium bisulfite in the Grocott Methenamine Silver technique?
Bleaches the section to remove unwanted stain left by chromic acid
