17 Questions
Which fluorochrome stain is used to screen for acid-fast bacilli and produces a yellow or orange fluorescence under a fluorescent microscope?
Auramine-rhodamine
Which stain is used to visualize the capsule surrounding certain yeasts, such as Cryptococcus species, by creating a dark background and a clear capsule around the yeast?
India Ink
Which stain is used to stain the cell walls of medically important fungi grown in slide culture?
Lactophenol Cotton Blue
Which stain is used to stain Corynebacterium diphtheriae for observation of metachromatic granules?
Methylene Blue
Which stain is used to visualize endospores, where the endospores appear green within pink- or red-appearing bacterial cells?
Endospore Stain
Which stain is a fluorochrome that binds to chitin in fungal cell walls, producing a bright apple-green or blue-white fluorescence?
Calcofluor White
Which of the following is the correct procedure for preparing a thin, monolayer smear?
Roll a swab back and forth across the slide to create the smear
Which of the following stains is used to specifically identify organisms?
Probe-mediated stains
What is the purpose of the Gram stain in a clinical microbiology laboratory?
To determine the cell wall structure and Gram-staining characteristics of organisms
What is the purpose of the acid-fast stain?
To identify organisms that are resistant to decolorization by acidic alcohol
Which of the following stains is commonly used in diagnostic microbiology laboratories?
All of the above
Which of the following is NOT a step in the Gram staining procedure?
Heating the primary stain
What is the primary purpose of the Gram staining technique?
To differentiate between Gram-positive and Gram-negative bacteria
Which of the following statements about Gram-negative bacteria staining is correct?
Pseudomonads, anaerobic bacilli, and thin-walled bacteria stain poorly with safranin
Which staining method is specifically designed for bacteria with high lipid and wax content in their cell walls?
Acid-fast staining
What is the difference between the Ziehl-Neelsen and Kinyoun acid-fast staining methods?
The Ziehl-Neelsen method uses heat, while the Kinyoun method is a cold or detergent method
Which of the following organisms can be identified using the acid-fast staining technique?
Mycobacteria, yeast, and coccidian parasites
Study Notes
Staining Procedures
- Decolorization: use 3.0% acid-alcohol (faint pink color remains)
- Counterstaining: Loeffler's methylene blue
- Washing: with water and deionized water
Common Stains Used for Microscopic Evaluation
- Auramine-rhodamine: fluorescent stain for acid-fast bacilli, appears yellow or orange under fluorescent microscope
- Acridine Orange: fluorochrome dye for gram-positive and gram-negative bacteria, appears bright orange under fluorescent microscope
- Calcofluor White: fluorochrome stain for fungal cell walls, appears bright apple-green or blue-white fluorescence
- Methylene Blue: for staining Corynebacterium diphtheriae to observe metachromatic granules
- Lactophenol Cotton Blue: for staining cell walls of medically important fungi grown in slide culture
- India Ink: negative stain for visualizing capsules surrounding certain yeasts, such as Cryptococcus spp.
- Endospore Stain: malachite green and safranin for visualizing endospores in bacterial cells
Gram Staining
- Results:
- Gram-positive bacteria: primary stain crystal violet appears dark blue to blue-black
- Gram-negative bacteria: counterstain safranin appears bright red
- Enterics have strong avidity and stain bright red
- Pseudomonads stain moderately well
- Anaerobic bacilli and other thin-walled bacteria stain weakly
Acid-Fast Staining
- Used for bacteria with high lipid and wax content in their cell walls
- Two methods: Ziehl-Neelsen stain (hot method) and Kinyoun stain (cold method)
- Used to identify Mycobacteria, yeast, Saccharomyces, and coccidian parasites such as Isospora belli, Cryptosporidium, and other coccidia-like bodies.
Categories of Stains
- Simple stains: forms and shapes
- Differential stains: specific components of elements present
- Probe-mediated stains: diagnostic antibody or DNA probe-mediated stains for identification of organisms
This quiz covers the staining techniques used in microscopic evaluation, including decolorization, counterstaining, and common stains like Auramine-rhodamine and Acridine Orange. Test your knowledge on different staining methods for bacteria.
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