Exercise 2: Carbohydrate Metabolism in Bacteria Flashcards
also known as sugars, are polyhydroxy aldehydes or ketones.
Carbohydrates
What is the most common universal carbon source?
Glucose, though bacteria can utilize other sugars.
Bacteria that use sugars as their primary carbon and energy sources.
chemoorganotrophic bacteria
Why is sugar metabolism important in bacterial identification?
The way bacteria metabolize carbohydrates helps classify and identify them.
Which tests are used to study bacterial sugar metabolism? (2)
- Oxidative-Fermentative (O-F) test
- MacConkey Agar test
What are the three main bacterial groups based on sugar metabolism? (3)
- Oxidative (Respiratory) Metabolism
- Fermentative Metabolism
- Non-saccharolytic
A process where bacteria use oxygen to break down carbohydrates, producing weak acids.
oxidative metabolism
A process that does not require oxygen and results in acidic byproducts.
fermentative metabolism
Bacteria that cannot utilize carbohydrates and depend on other energy sources like proteins or amino acids.
non-saccharolytic mean
What are the objectives of the laboratory activity?
- Perform the O-F test to determine carbon utilization ability.
- Identify whether the bacteria can ferment lactose using MacConkey Agar.
- Explain the principles behind the Hugh and Leifson and MacConkey Agar tests.
What is the purpose of the Oxidative-Fermentative (O-F) test?
- To determine whether a bacterium metabolizes carbohydrates oxidatively, fermentatively, or not at all.
- To differentiate Gram-negative rods based on their ability to metabolize glucose via fermentation or oxidation.
What is the function of peptone (tryptone) in the O-F test?
It serves as an alternative energy source when bacteria do not utilize carbohydrates.
Why is sodium chloride (NaCl) included in the O-F medium?
It helps maintain osmotic balance in the medium.
What is the main energy source for bacterial metabolism in the O-F test?
Carbohydrate solution (e.g., glucose).
What is the role of bromothymol blue in the O-F test?
It is a pH indicator that changes color based on bacterial metabolism.
Why is agar included in the O-F medium?
Why is agar included in the O-F medium?
What is the function of K₂HPO₄ (dipotassium phosphate) in the O-F test?
It acts as a buffer, maintaining a stable pH in the medium.
What is the role of distilled water (DH₂O) in the O-F test?
It serves as the solvent for all components in the medium.
What does the O-F test determine?
➡️ Whether bacteria metabolize carbohydrates through: (3)
- Fermentation
- Oxidation (aerobic respiration)
- Nonsaccharolytic pathways
What happens in fermentative metabolism?
High acid production → Bromothymol blue turns yellow in both aerobic and anaerobic tubes.
What happens in oxidative metabolism?
Weak acid production → Yellow color change occurs only in the aerobic tube.
What happens in nonsaccharolytic metabolism?
No acid production → No color change or blue color due to protein metabolism.
What is Hugh and Leifson’s O-F Basal Medium used for?
It is used in the Oxidative-Fermentative (O-F) test to differentiate bacteria based on their carbohydrate metabolism.
A special method used for sterilizing heat-labile materials that cannot withstand autoclaving.
Filter sterilization
How does filter sterilization work?
It uses a micropore filter (0.22 microns) to remove bacteria while allowing sterilized liquid to pass through.
Why is a 0.22-micron filter used?
It is small enough to block most bacteria, which typically range from 0.2 to 2 micrometers in size.
It is used to isolate Gram-negative enteric bacteria and differentiate lactose fermenters from non-fermenters.
MacConkey Agar
What provides essential nutrients for bacterial growth in MacConkey Agar?
Pancreatic digest of gelatin and peptones (meat and casein).
What is the fermentable carbohydrate source in MacConkey Agar?
Lactose monohydrate
Which components inhibit Gram-positive bacteria?
Crystal violet and bile salts
What maintains osmotic balance in MacConkey Agar?
Sodium chloride (NaCl)
What is the pH indicator in MacConkey Agar?
Neutral red, which turns red below pH 6.8 and is colorless above pH 6.8.
What is the role of agar in MacConkey Agar?
It acts as the solidifying agent.
How does MacConkey Agar differentiate lactose fermenters? (2)
➡️ Lactose fermentation produces organic acids, lowering the pH.
➡️ Neutral red turns bright red/pink when the pH drops below 6.8, indicating lactose fermentation.
