lab 4 Flashcards
A gram stain was prepared and the result was purple cocci in pairs. Would you expect to see growth if this organism was cultured on a MacConkey agar plate?
Select Answer:
Yes
No
Impossible to tell from information given
Maybe
no
from lab 4 pre-quiz
While some agar media will grow many microbes, there are agar media that are used because they “select” for only certain types of microbes and then show “differences” between those that do grow on it. This is called Selective and Differential agar. Which agar medium shown in the list is both selective and differential?
Select Answer:
mannitol salt agar
Sabouraud’s agar (Sabouraud’s dextrose agar)
Blood agar medium
Nutrient agar
mannitol salt agar
from lab 4 pre-quiz
-urea broth reactions.
The bacterium in one tube turned the medium pink because it was able to produce ______, an enzyme that hydrolyzes urea into ammonia and carbon dioxide.
Urease
explanation:
Urea digestion occurs if the bacterium produces an enzyme (urease) to break it down into ammonia and carbon dioxide. The ammonia raises the pH of the medium and turns the pH indicator dye in the medium pink. The original color of the medium at a neutral pH is beige.
(from lab 4 pre-quiz)
A lactose carbohydrate fermentation tube was inoculated and the result was that the medium was yellow and the durham tube was filled with gas. The result of this test is:
Select Answer:
a. Acid produced
b. Negative for fermentation and no gas produced
c. Acids and gas produced
d. Negative for fermentation with gas produced
Acids and gas produced
Glucose and Lactose broth
Key ingredients?
What does the microbe bring to the reaction?
Key potential end products and observations?
Contains: less than 1% glucose or lactose, pH indicator (phenol red)
Some organisms have special enzyme pathways that can “ferment” glucose or lactose.
If carbohydrate fermentation occurs
Acids are produced lowering the pH, the pH indicator changes color from red to yellow.
Possibly gas is also produced and is shown by some being trapped in the Durham tube which is inverted in the larger tube.
Urea broth
Key ingredients?
What does the microbe bring to the reaction?
Key potential end products and observations?
The broth contains: Urea broth, Phenol red (pH indicator)
Some organisms produce the enzyme urease which hydrolyzes urea into ammonia and gas (carbon dioxide).
Ammonia is not an acid – it is a base and will increase the pH in the tube. Increase pH changes the indicator dye from salmon color to a rose/dark pink color.
Citrate Slant
Key ingredients?
What does the microbe bring to the reaction?
Key potential end products and observations?
Agar contains: Citrate as sole carbon source and Bromothymol blue (pH indicator)
Some organisms can use citrate (aka citric acid) as its sole carbon source
If citrate is used, this acid is slowly removed from the agar and the pH increases causing the pH indicator to change from green to blue color.
SIM agar: “S” sulfide production
Key ingredients?
What does the microbe bring to the reaction?
Key potential end products and observations?
S for sulfide production
Agar contains cysteine and iron (Fe)
Some organism produce enzymes that hydrolyze cysteine (amino acid) into alanine and hydrogen sulfide (H2S or HS ions).
H2S or HS ions binds to iron ions (Fe) in the agar to produce iron sulfide (FeS) which causes the medium to turn black.
SIM agar: “I” Indole test
Key ingredients?
What does the microbe bring to the reaction?
Key potential end products and observations?
agar contains tryptophan
Some organisms produce the enzyme tryptophanase
Enzyme breaks down tryptophan to indole, pyruvic acid, and ammonia.
When adding a few drops of Kovac’s reagent to the top of the agar, the reagent will turn red if indole is present. Red chemical is red quinoidal compound.
Carbohydrate fermentation
Carbohydrates can be metabolized by aerobic respiration, anaerobic respiration, and fermentation.
Fermentation is an anaerobic process by which organisms INCOMPLETELY breaks down organics into various end products (acids, gases, alcohols).
Involves glycolysis + unique fermentation pathway
Not all bacteria ferment all substrates.
pH indicator: phenol red
Used in lactose, glucose, and urea tests
Changes color at different pH
Any change from control means something is going on.
Two main causes of mutation of DNA?
Induced mutations = those where are mutagen caused the damage
spontaneous mutation = those where DNA randomly mutates on its own as an error of replication
*The damage to the DNA leads to either non-lethal mutation or lethal mutations
What is normal base pairing in DNA
A-T and C-G
What does photo-activated mean?
Some of those enzymes are photo-activated meaning that in the presence of light, the repair enzymes are produced and/or are go to work.
Carbohydrate fermentation
Key ingredients before inoculation?
what does the microbe bring to the reaction?
Key potential end products and observations?
Color?
Carbohydrate (glucose and lactose), Phenol red (pH indicator)
Enzymes that ferment the carbohydrate
Acid (yellow) and gas (trapped air)
Red to yellow (acids + gas = yellow colored broth)
