LAB MODULE: STAINING– STUDY HELP Instructions: Read the Staining lab document on

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LAB MODULE: STAINING– STUDY HELP

Instructions: Read the Staining lab document on Late Nite Labs. Answer the questions on this study help document in preparation for the Pre-Lab Quiz on Canvas. This document will also help you on your Late Nite Labs quiz.

Which of the following statements is/are true concerning bacteria? (For each false statement, know why the statement is false.)

o   It is necessary to stain bacteria because they are colorless and invisible under a light microscope.
o   Heat fixation kills bacteria and makes them adhere to the slide.
o   Scientists only use one stain when staining bacteria.

List and define the three bacterial shapes.

List the four arrangements of bacteria. (You have three typical arrangements. Bacteria can also be dispersed individually.)

What characteristic does the Gram method use to distinguish between Gram-positive and Gram-negative bacteria?

Label each statement as describing Gram-positive bacteria, Gram-negative bacteria, or both.

o   Have thin cell walls that allow ethanol to wash out the dye-iodine complexes
o   Counterstain makes the invisible bacteria pink after decolorization.
o   Have thick cell walls with a high percentage of peptidoglycan.
o   Retain the primary purple stain.
o   Look purple after using the Gram method to stain bacteria.
o   Look pink after using the Gram method to stain bacteria.

For the Gram method:

•   What is the primary stain?
•   What is the decolorizer?
•   What is the counter-stain?

The following picture is Staphylococcus aureus.

•   Is this species Gram-positive or Gram-negative?
•   What is the shape of each bacterium?
•   What is the arrangement of the bacteria?

For the Acid-Fast stain method:

•   What is the primary stain?
•   What is the decolorizer?
•   What is the counter-stain?

Which of the following statements is/are true concerning Acid-Fast staining? (For each false statement, know why the statement is false.)

o   Acid-fast positive bacteria cannot be identified by Gram staining because their waxy cell walls repel Gram staining.
o   When preparing microscope slides of acid-fast bacteria, scientists use serum to help cells adhere to the slide.
o   Acid-fast positive bacteria look pinkish purple under a microscope (after the staining procedures).
o   Acid-fast negative bacteria have no color under the microscope (after the staining procedures).
o   The bacterium responsible for tuberculosis is acid-fast positive.
o   The bacterium responsible for leprosy is acid-fast negative.

For the endospore staining method:

What is the primary stain?

What is the counter-stain?

Which of the following statements is/are true concerning endospores? (For each false statement, know why the statement is false.)

o   Most bacterial genera produce spores.
o   Spore-producing bacteria produce endospores in response to stress (e.g., lack of nutrients).
o   Endospores are more durable than active bacteria.
o   The bacterial species that causes anthrax can produce spores.
o   A scientist must steam a microscope slide in order to force the primary stain into the spores.
o   Scientists have to observe cultures grown for different lengths of time (e.g. after two days, again after five days) so that they can observe endospores within bacteria and released endospores.

Which of the following statements is/are true concerning capsule staining? (For each false statement, know why the statement is false.)

o   Capsules are found outside the cell wall of some species of bacteria.
o   Capsules are made of mucous and repel aqueous stains.
o   During capsule staining, the capsule resists staining and appears as a white ring around the cell.
o   Heat can cause bacteria to shrink and may make bacteria appear to have a capsule when they do not.
o   Heat can shrink capsules and make them more difficult to detect.
o   Capsules make it harder for bacteria to adhere to surfaces.
o   The capsule prevents phagocytosis of the bacterium.
o   Capsules decrease the ability of bacteria to cause disease.

Once you answer all of the questions on this study help document, go to the Staining lab module and submit the Staining Pre-Lab Quiz.

Then, go to the Late Nite Labs course site and complete all Staining lab activities.

After you finish the Staining lab activities on Late Nite Labs, submit the Staining multiple choice quiz on Late Nite Labs.

Explanation / Answer

a) Which of the following statements is/are true concerning bacteria?

Most of the bacteria are generally colorless and invisible because of their lack of contrast with the water in which they may reside, staining is necessary in order to make them readily visible for observation of intracellular structures as well as overall morphology.
Heat fixation step makes the bacteria suitable for further steps of the experiment.
Scientist use only one stain in basic staining techniques.

b) List and define the three bacterial shapes.
The three most common bacterial shapes are as follows

c) List the four arrangements of bacteria.

The four arrangements of bacteria are given as:

Round bacteria (Cocci)

Rod-shaped bacteria (Bacilli)

Spiral bacteria (Spirilla)

d) What characteristic does the Gram method use to distinguish between Gram-positive and Gram-negative bacteria?
The Gram-positive and Fram-negative bacteria are characterized on the basis of cell wall structure and its ability to retain the crystal violet dye of Gram stain. Gram positive bacteria have thick cell walls with a high percentage of peptidoglycan, therefore the cell wall retains the stain even after alcohol washing.

e) Label each statement as describing Gram-positive bacteria, Gram-negative bacteria, or both.

o   Have thin cell walls that allow ethanol to wash out the dye-iodine complexes: Gram-negative bacteria
o   Counterstain makes the invisible bacteria pink after decolorization: Gram-negative bacteria
o   Have thick cell walls with a high percentage of peptidoglycan: Gram-positive bacteria
o   Retain the primary purple stain: Gram-positive bacteria
o   Look purple after using the Gram method to stain bacteria: Gram-positive bacteria
o   Look pink after using the Gram method to stain bacteria: Gram-negative bacteria.

f) For the Gram method:

•   What is the primary stain? Crystal violet
•   What is the decolorizer? Ethyl alcohol
•   What is the counter-stain? Safranin

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