Gram Staining and Bacterial Structure Quiz

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Questions and Answers

What is the primary component of the cell wall in Gram-positive bacteria?

Peptidoglycan (correct)

Outer membrane

Lipopolysaccharides

Protein fibers

Who originally developed the Gram staining technique?

Hans Christian Gram (correct)

Robert Koch

Carl Weigert

Louis Pasteur

Which step did Carl Weigert add to the original Gram staining process?

Decolorizing with acetone

Staining with safranin (correct)

A second alcohol wash

Heating the bacterial smear

What color do Gram-negative bacteria appear after the Gram staining process?

Pink Signup and view all the answers

Why do Gram-positive bacteria retain the crystal violet stain?

Their thick peptidoglycan layer prevents extraction. Signup and view all the answers

What happens to Gram-negative bacteria when alcohol is applied during the staining process?

The dye is extracted due to a thin cell wall. Signup and view all the answers

Which type of bacteria has an additional outer membrane?

Only Gram-negative Signup and view all the answers

During the Gram staining procedure, what role does the alcohol play?

It dehydrates and extracts the stain from Gram-negative bacteria. Signup and view all the answers

What is the primary external factor that leads to endospore formation in bacteria?

Exhaustion of nutrients Signup and view all the answers

During the activation phase of endospore germination, which of the following is NOT a method to damage the spore coat?

Cooling Signup and view all the answers

What color is associated with Gram-positive bacteria after gram staining?

Blue to purple Signup and view all the answers

Which of the following statements about the catalase test is accurate?

It differentiates between aerobic and anaerobic bacteria. Signup and view all the answers

What occurs during the outgrowth phase of endospore germination?

Water uptake and swelling of the endospore Signup and view all the answers

Which layer of gram-negative bacteria allows alcohol to penetrate easily during gram staining?

Outer lipid-rich layer Signup and view all the answers

Which process is responsible for the rapid degradation of cortex peptidoglycan during endospore germination?

Activation of autolysin Signup and view all the answers

What is the result of gram staining for Escherichia coli?

Pink to red Signup and view all the answers

What is the primary function of the catalase enzyme?

To catalyze the decomposition of hydrogen peroxide Signup and view all the answers

Which of the following organisms is known to be catalase positive?

Staphylococcus spp. Signup and view all the answers

What is evident from the lack of bubbling in a catalase test?

The organism is catalase negative Signup and view all the answers

Under which condition is 15% hydrogen peroxide used in the catalase test?

Anaerobic conditions Signup and view all the answers

Which characteristic is used to demonstrate motility in bacteria?

Rotating flagella Signup and view all the answers

What type of agar medium is used to demonstrate bacterial motility?

Semi-solid agar Signup and view all the answers

Which of the following bacteria is motile?

Escherichia coli Signup and view all the answers

Lactose fermentation tests are primarily used for what purpose?

To identify pathogenic bacteria Signup and view all the answers

What is the primary purpose of carbohydrate fermentation tests?

To determine if a microorganism can ferment specific carbohydrates Signup and view all the answers

How is lactose fermentation determined in a fermentation medium?

By observing a color change in a pH indicator Signup and view all the answers

Which pH indicator turns yellow at an acidic pH of 6.8 or below?

Phenol Red Signup and view all the answers

What does a positive result in a Durham tube indicate?

Fermentation has occurred with gas production Signup and view all the answers

Which of the following statements is true about the Enterobacteriaceae family?

All members are classified as glucose fermenters. Signup and view all the answers

What effect does acid production have on the pH of the fermentation medium?

It decreases the pH to below 5.0. Signup and view all the answers

What color does Andrade’s Indicator turn at an acidic pH of around 5.0?

Dark pink to red Signup and view all the answers

How do phenol red and bromothymol blue differ at a neutral pH?

Phenol red is reddish orange, bromothymol blue is green. Signup and view all the answers

Study Notes

Food Microbiology - FST 101

Course: Food Microbiology (FST 101)
Institution: Central Bicol State University of Agriculture
Instructor: Alessandra M. Domanico, Assistant Professor IV
Topics Covered: Gram Staining, Endospore Formation, Catalase Test, Motility, and Fermentation Test

Gram Staining

Developed by: Hans Christian Gram (1853), a Danish physician
Initial Work: Studied botany at the University of Copenhagen and discovered that certain stains are preferentially absorbed by bacterial cells.
Early Process: His initial work focused on Streptococcus pneumoniae and Klebsiella pneumoniae.
Refinement by: Carl Weigert (1845-1904), a German pathologist, added a final step using safranin as a counterstain.
Importance: Gram staining remains the most crucial method to distinguish between major bacterial classes.

Gram Staining Procedure

Preparation of Smear:
- Spread the bacterial culture thinly on a glass slide.
- Air dry the smear.
- Fix the smear by passing the slide through a flame.
Staining Procedure:
- Flood the heat-fixed smear with crystal violet for 1 minute. All cells will be purple.
- Add iodine solution for 3 minutes. All cells remain purple.
- Decolorize with alcohol briefly (about 20 seconds).
- Gram-positive cells remain purple, gram-negative cells become colorless.
- Counterstain with safranin for 1-2 minutes. Gram-positive cells are purple, gram-negative cells are pink to red.

Gram Staining Results

Gram-positive Bacteria: Appear purple under a microscope
Gram-negative Bacteria: Appear pink to red under a microscope

Relationship of Cell Wall Structure to Gram Stain

Gram-positive Bacteria: Possess a thick peptidoglycan mesh in their cell wall (50-90%). This thick layer prevents the decolorizing agent from extracting the crystal violet.
Gram-negative Bacteria: Have thinner peptidoglycan layer (10%) and an additional outer membrane containing lipids. This outer membrane allows the decolorizing agent to easily wash away the crystal violet.

Endospore Formation

Formation Trigger: Endospores form in response to unfavorable environmental conditions, commonly nutrient depletion.
Spores vs. Vegetative Cells:
- Vegetative Cells: Active, living cells that ingest nutrients and secrete waste materials.
- Spores: Dormant cells (not actively metabolizing) highly resistant to heat, cold, chemicals, and radiation. This is a survival mechanism, allowing the bacterium to endure harsh conditions and resume its vegetative stage later.

Endospore Formation Diagram

A series of detailed steps depict the formation process of endospores.
The cycle includes steps like chromosome duplication, septation, spore coat formation, and the release of the mature endospore.

Endospore Formers

Lists of various bacteria types that form endospores, including species and groups of bacteria (aerobic types, personnel contamination, and water/water sources).

Catalase Test

Purpose: To detect the presence of the enzyme catalase, which is important to differentiate aerobic and anaerobic bacteria.
Catalase Enzyme Function: A common enzyme in organisms surviving in oxygen, catalyzes the decomposition of hydrogen peroxide into water and oxygen.
Principle of Catalase Test:
- A small bacterial inoculum is introduced into hydrogen peroxide.
- If catalase is present, rapid oxygen release causes bubbling.
- Lack of catalase produces either no or a very weak bubble response.

Motility

Defined: The ability of an organism to move by itself.
Types: Propeller-like flagella in bacteria or gliding motility through special fibrils.
Flagellar Structure: The flagella is rigid and helical and generates motility through rotation.
Motility Testing: Demonstrated by observing the bacteria in a semi-solid agar medium.

Lactose Fermentation Tests

Purpose: Identifying bacteria's ability to ferment lactose as a carbon source.
Mechanism: If lactose is fermented, acid byproducts are generated, causing a pH drop in the medium, noticeable by a change in color using a pH indicator.

Requirements for Carbohydrate Tests

Media: Carbohydrate broth, containing specific sugars (i.e., dextrose, sucrose, and lactose).
Indicators: Include Andrade's indicator, Phenol Red, Bromocresol Purple, or Bromothymol Blue to determine the carbohydrate fermentation.
Durham Tube: A small inverted tube used to detect gas production(CO2) during fermentation by observing the presence of bubbles.

Methyl Red and Voges-Proskauer (MR-VP) Test

Purpose: Characterize bacterial metabolism through differentiation and classification.

Bacterial Identification and Classification

Basis: Gram reaction, endospore formation, morphology, and other distinguishing features.
Methodology: Often employs a dichotomous key to track similarities and differences among bacterial genera in a systematic manner.

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Description

Test your knowledge on Gram staining and bacterial structures with this quiz. Covering components of Gram-positive and Gram-negative bacteria, the quiz also delves into endospore formation and germination processes. Perfect for students of microbiology looking to reinforce their understanding.