MCB 2010C FINAL LAB EXAM QUESTION AND
ANSWER (2024-2025) A+ RATED EXPERT VERIFIED
Question 1
What kind of media is EMB?
complex, selective, and differential
Question 2
What is the EMB media composed of?
gelatin, lactose, and the dyes eosin Y and methylene blue
Question 3
What kind of microbe does EMB agar inhibit?
gram positive
Question 4
If the bacterium changes to a purple color on EMB agar, what does that mean?
The bacterium is gram negative, and ferments lactose.
Question 5
What bacterial stocks turn purple on EMB agar, meaning that they ferment lactose?
Enterobacter aerogenes, Proteus vulgaris, and Esherichia coli
MCB 2010C FINAL LAB EXAM
,Question 6
What sheen does E. coli give off on EMB agar?
A metallic green sheen
Question 7
What kind of media is MAC?
Selective and differential
Question 8
What is the MAC media composed of?
Lactose, bile salts, neutral red, and crystal violet.
Question 9
What is the action of bile salts and crystal violet in MAC media?
Inhibits gram positive bacteria growth
Question 10
What is the pH indicator in MAC media?
Neutral red
Question 11
If a bacterium does alter the color of MAC media, what does this mean?
The bacterium is gram negative, lactose fermenting, lowers the pH of the media (acidic) and changes
the media from pink to red.
Question 12
What bacterial stocks turn red on MAC agar, meaning that they ferment lactose and lower pH?
Escherichia coli and Enterobacter aerogenes
MCB 2010C FINAL LAB EXAM
, Question 13
What is the pH indicator in PR-G tubes?
Phenyl red
Question 14
If the bacterium changes to a yellow color, what does this mean? pink?
If the media turns yellow, this indicates glucose fermentation, and an acidic pH. If the media turns
pink, this indicates peptone from NH3 production, raising the pH alkaline.
Question 15
What does the durham tube in the PR-G tube indicate?
Gas production indicates fermentation.
Question 16
What bacterium changes yellow in PR-G media?
Enterobacter aerogenes, Escherichia coli, and proteus vulgaris (both produced gas)
Question 17
What kind of media is PR-G and PR-L tubes?
Differential
Question 18
What bacterium changes to yellow on PR-L media, meaning it ferments lactose?
Enterobacter aerogenes and Escherichia coli (both produced gas)
Question 19
What kind of media is urea broth?
Differential
MCB 2010C FINAL LAB EXAM
ANSWER (2024-2025) A+ RATED EXPERT VERIFIED
Question 1
What kind of media is EMB?
complex, selective, and differential
Question 2
What is the EMB media composed of?
gelatin, lactose, and the dyes eosin Y and methylene blue
Question 3
What kind of microbe does EMB agar inhibit?
gram positive
Question 4
If the bacterium changes to a purple color on EMB agar, what does that mean?
The bacterium is gram negative, and ferments lactose.
Question 5
What bacterial stocks turn purple on EMB agar, meaning that they ferment lactose?
Enterobacter aerogenes, Proteus vulgaris, and Esherichia coli
MCB 2010C FINAL LAB EXAM
,Question 6
What sheen does E. coli give off on EMB agar?
A metallic green sheen
Question 7
What kind of media is MAC?
Selective and differential
Question 8
What is the MAC media composed of?
Lactose, bile salts, neutral red, and crystal violet.
Question 9
What is the action of bile salts and crystal violet in MAC media?
Inhibits gram positive bacteria growth
Question 10
What is the pH indicator in MAC media?
Neutral red
Question 11
If a bacterium does alter the color of MAC media, what does this mean?
The bacterium is gram negative, lactose fermenting, lowers the pH of the media (acidic) and changes
the media from pink to red.
Question 12
What bacterial stocks turn red on MAC agar, meaning that they ferment lactose and lower pH?
Escherichia coli and Enterobacter aerogenes
MCB 2010C FINAL LAB EXAM
, Question 13
What is the pH indicator in PR-G tubes?
Phenyl red
Question 14
If the bacterium changes to a yellow color, what does this mean? pink?
If the media turns yellow, this indicates glucose fermentation, and an acidic pH. If the media turns
pink, this indicates peptone from NH3 production, raising the pH alkaline.
Question 15
What does the durham tube in the PR-G tube indicate?
Gas production indicates fermentation.
Question 16
What bacterium changes yellow in PR-G media?
Enterobacter aerogenes, Escherichia coli, and proteus vulgaris (both produced gas)
Question 17
What kind of media is PR-G and PR-L tubes?
Differential
Question 18
What bacterium changes to yellow on PR-L media, meaning it ferments lactose?
Enterobacter aerogenes and Escherichia coli (both produced gas)
Question 19
What kind of media is urea broth?
Differential
MCB 2010C FINAL LAB EXAM
