Staining Name: ————-
20 pts.
Objectives:
1.- Know the steps to prepare a smear of bacteria for microscopic examination.
2.- Explain the purpose of staining bacterial cells. Explain purpose of heat fixing a smear
3.- Identify the general characteristics, and morphologies of microbes that can be visualized by staining.
4.- Learn how to correctly prepare and simple stain a bacterial smear from a liquid culture, and from a colony
5.- Explain the differences between simple staining, and differential and structural stains.
6.- Describe how the Gram stain works and summarize the differences in cell wall structure of gram positive and gram-negative cells. List the Gram stain reagents, steps, and purpose of each. Recognize some common mistakes that can affect a Gram stain.
7.- Describe the purpose, reagents, and procedure of the acid-fast stain. Know the genus of medically important acid-fast organisms. Recognize some common mistakes that can affect an Acid-Fast Stain
8.- Describe endospores and the differences between endospore and vegetative cells. Name bacteria genera that are endospore formers.
9.- Describe the purpose, reagents, and procedure of the endospore stain. Recognize some common mistakes that can affect an endospore stain.
10.- Describe the structure and function of bacterial capsules. Describe a negative staining technique. Describe the purpose, reagents, and procedure of the capsule stain. Recognize some common mistakes that can affect a capsule stain.
1.- Staining: Smear Preaparation (3.0 pts.)
A smear is a sample of bacteria taken from a culture and spread onto a clean microscope slide
1.- (1 pt.) Use the space below to load the picture of an unstained vs. stained sample from the virtual lab exercise. Use the pictures to explain the purpose of staining.
2.- (1 pt.) Staining problems: Heat fixing
What happens if the smear is not heat fixed long enough? Or heat fixed for too long?
What happens is the smear is prepared using an excessive amount of sample?
What happens if the smear is prepared using not enough sample?
Bacterial smears can be prepared from broth or agar media, or from clinical specimens.
3.- (1 pt.) When preparing a smear from a Petry plate, the sample of bacteria is picked from an isolated colony. What is an isolated colony?
Why is it important to pick the sample from one isolated colony?
2.- Bacterial Staining: Introduction (1 pts.)
1.- (1 pt.) Match the reagents used in a differential with their purpose:
———-Decolorizer A.- second dye applied during a differential stain.
———-Primary stain B.- removes the first dye from a bacterial cell
———-Countersatin C.- first dye applied during a differential stain
3.- Bacterial Staining: Gram Stain (5 pts.)
The gram stain is the most important stain in microbiology. It helps to identify and characterize bacteria which leads to choosing an appropriate treatment method.
1.- (1 pt.) Give two differences between Gram positive, and Gram-negative cell walls.
2.- (1 pt.) List the reagents used in a gram stain by writing their names next to the functions listed.
