1. If you were to make Columbia CNA with 5% sheep blood agar plates with twice a
ID: 94787 • Letter: 1
Question
1.
If you were to make Columbia CNA with 5% sheep blood agar plates with twice as much colistin, how would the results likely be affected?
Select one:
a. Less Gram-positive growth, more Gram-negative growth
b. Less Gram-positive growth, no or even less Gram-negative growth
c. More Gram-positive growth, more Gram-negative growth
d. More Gram-positive growth, no or even less Gram-negative growth
e. Same Gram-positive growth, no or even less Gram-negative growth
2.
In Mannitol Salt Agar lab, you were told to invert the plate before incubation. This is a common practice to avoid:
Select one:
a. Condensation drops
b. Increased smell
c. Decrease oxygen content
d. Bacteria from growing in wrong direction
e. Airborne contamination
3.
If you see a yellow halo surrounding a colony on a MSA plate, which of the following is likely to be true?
Select one:
a. Glycolysis occurred
b. The organism is Staphylcoccus epidermidis
c. Colonies are not isolated
d. Fermentation occurred
e. Colony is Gram-negative
4.
Which one of the following is found in MSA plates, but not in NA plates?
Select one:
a. Phenol red
b. Agar
c. Tryptose
d. Peptone
e. Beef extract
5.
Why are the three organisms of Phenylethyl Alcohol Agar lab inoculated on the same plate?
Select one:
a. To avoid contamination
b. For easy viewing purposes.
c. To save resources
d. To avoid fluctuations in medium content and environmental effects.
6.
For which reason would you most likely use a PEA plate for culturing after taking a sample from a patient?
Select one:
a. To isolate Streptococcus and Staphylococcus from other fecal bacteria.
b. To detect Escherichia contamination on the skin.
c. To find E. coli strains associated with food poisoning.
d. To identify gram-negative anaerobes in the patient's flora.
Explanation / Answer
Ans.
1) Colistin and Nalidixic acid are selective only allowing for growth of gram positive species not for gram negative. Hence option (D) is correct
less gram positive growth, more gram negative growth, Hence option (A) is incorrect.
less gram postive growth, no or even less gram negative growth is not possible, Hence option (B) is incorrect
More gram positive growth and more gram negative growth is not possible, Hence option (C) is incorrect
2) i. Prevent contamination from condensation
ii. Prevent smearing of colonies with condensation, Hence option (A) is correct
Before incubation invert the plate increased smell , Hence option (B) is incorrect
Before incubation invert the plate decreased oxygen is not take place, Hence option (C) is incorrect
Before incubation invert the plate airborne contamination , Hence option (D) is incorrect.
3) Yellow halo surrounding a colony on a MSA plate due to if particular speciment contains like S.aureus, it ferments mannitol (whenever sugar is fermented acid is produced) and changes pH level below 6.9, the medium is yellow. Hence option (D) is correct.
Glycosis is not occur in microbial fermentation, Hence option is (A) is incorrect.
Organism staphyloccous epidermidis (gram positive ) growth but no yellow halo Hence option is (B) is incorrect.
colonies is not isolated, Hence option is (C) is incorrect
gram negative no growth, Hence option is (E) is incorrect.
4) Phenol red is found in MSA but not in NA plate because phenol red is a indictor is pH indicator. Hence option (A) is correct.
Agar is found in both MSA and NA plates Hence option (B) is incorrect
Beef extract is found in both MSA and NA plates, Hence option ( E ) is incorrect
Tryptose is found in both MSA and NA plates, Hence option (C) is incorrect
peptone is found in both MSA and NA plates, (D) is incorrect
5) To avoid fluctuations in medium content and enivornmental effects, Hence option is correct
6) This media selective for gram positive streptoccoci, staphylococci and other fecal bacteria, Hence option (A) is correct.
E.coli is gram negative is not specific for PEA plate, Hence option (B) is incorrect.
E.coli is gram negative and also speciemen collect from urine and wound not for food poison, Hence option (C) is incorrect.
To identify gram-negative anaerobes in the patients flora Hence option (D) is incorrect.
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