Columbia CNA with 5% Sheep Blood Agar Columbia CNA recipe: pancreatic digest of
ID: 169189 • Letter: C
Question
Columbia CNA with 5% Sheep Blood Agar
Columbia CNA recipe: pancreatic digest of casein, peptic digest of animal tissue, yeast extract, beef extract, corn starch, sodium chloride, colistin, naldixic acid, agar, distilled or deionized water, sheep blood.
1. Which ingredients in Columbia CNA plus 5% sheep blood agar supply(ies) (a.Carbon) (b. Nitrogen)?
2. a.) Growth on the Columbia CNA and NA plates was recorded as ''good growth,'' ''poor growth,'' or ''no growth.'' These are qualitative and, at least for the first two, subjective terms. What did you use to establish what constituted ''good growth?'' b.) Why wouldn't it be advisable to compare growth of the organisms on each plate to each other? There are at least two answers to this question.
Mannitol Salt Agar
3. a.) Growth on the Mannitol Salt Agar and NA plates was recorded as ''good growth,'' ''poor growth,'' or ''no growth.'' These are qualitative and, at least for the first two, subjective terms. What did you use to establish what constituted ''good growth?'' b.) Why wouldn't it be advisable to compare growth of the organisms on each plate to each other? There are at least two answers to this question.
4. Suppose a mistake is made in preparing a batch of MSA and the starting pH is 7.8 instead of 7.2-7.6. Would that affect the mediums sensitivity or specificity? Explain your answer.
I WOULD REALLY APPRECIATE SOME HELP WITH THESE QUESTIONS. I WILL RATE CORRECT ANSWERS. THANK YOUR VERY MUCH. MICROBIOLOGY LAB.
Explanation / Answer
1. Which ingredients in Columbia CNA plus 5% sheep blood agar supply(ies) (a.Carbon) (b. Nitrogen)?
A. Carbon source - Corn Starch
B. Nitrogen source - Pancreatic digest of casein, Peptic digest of animal tissue, Yeast extract,
2. a.) Growth on the Columbia CNA and NA plates was recorded as ''good growth,'' ''poor growth,'' or ''no growth.'' These are qualitative and, at least for the first two, subjective terms. What did you use to establish what constituted ''good growth?'' b.) Why wouldn't it be advisable to compare growth of the organisms on each plate to each other? There are at least two answers to this question.
a. Good growth means the plate contains many colonies, Poor growth means the plat contains countable number of colonies and no growth means the plate does not contain colonies.
b. It is not advisable to compare growth of the organisms on each plate to each other because the number of cells present in each colony cannot be compared.
The CFU/ml or O.D/ml is the best method to estimate the number of colonies. Because different organism has different growth media, and the size of the colony differs with different organisms, more over the starting population is different for different organism.
The Columbia CNA agar is a differential media and allows only certain type of organisms such as gram positive to grow on it, where as NA is a general media which allows all type of bacteria to grow.
3. The answer is same as that of question 2.
4. It will affect the mediums sensitivity and not specificity, It will allow only growth of salt tolerant gram positive bacteria and it also enables to distinguish the acid producers from non acid producers, Thus the pH change will affect only the sensitivity of the media but not the specificity.