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Explanation:
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Answer:
A serial dilution and the following plating experiment is done in order to determine the actual amount of bacteria/microbes in a specific volume of soil sample. As a standard test, a set volume of the lower dilution is obtained and positioned on a median plate and permitted to increase for the needed amount of time. The amount of colonies is evaluated and thus the overall Colony Forming Units (CFU) is determined by unit volume of the sample plated and therefore the volume of soil sample employed.
Therefore,
The calculation is done using:
CFU/ml = Number of colonies appeared × dilution factor / volume plated
Given,
Number of colonies appeared = 97
dilution factor = 10^(-6)
volume plated = 1/10 = 0.1
This will help us calculate it as:
CFU/ml = 97 * 10^(-6) / 0.1
= 97 * 10^(-7) CFU/ml
This CFU/ml helps determine the amount of bacterial colonies per unit volume of sample plated.
Given,
The original sample as 1g or 1000 mg of soil in its total volume.
Therefore,
The number of bacteria can be calculated using:
Amount of bacteria in original sample
= 97 * 10^(-7) CFU/ml × 1/ 1000 mg
= 9.7 * 10^(-3) CFU/mg
A. and B. Hope this helped
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The EMB (Eosin Methylene Blue) agar is a selective and differential agar medium. It contains sucrose and lactose as fermentable substrates together with Eosin Y and methylene blue dyes which in combination gives the agar its characteristic color when prepared and serves as a pH indicator as well as an inhibitor of growth of Gram-positive bacteria. Hence, it is primarily used to isolate Gram-negative fecal coliforms while some positive fecal coliforms such as Staphylococci are also able to grow.
These coliforms are of two types:
- Lactose or sucrose fermenting coliforms form metallic sheens on the agar as a result of acid production and the response of the indicator to the increased acidity.
- Non-lactose/sucrose fermenters are only able to produce acid by protein deamination. Hence they either form colorless or pinkish colonies on the agar
On the other hand, Mannitol salt agar is a selective and differential agar medium that is primarily used to isolate Staphylococcal bacteria. The presence of sodium chloride in the medium makes it a partial or complete inhibitor of other bacteria.
Hence, an unknown bacterium that forms colorless colonies on EMB will either be a non-lactose fermenting, Gram-negative coliform that will hardly grow on Mannitol salt agar, or a Gram-positive fecal Staphylococcus.
Staphylococci bacteria are of two types:
- Coagulase-positive will form yellow colonies on the Mannitol salt agar.
- Coagulase-negative will form red colonies on the Mannitol salt agar.
More about isolating media can be found here: https://brainly.in/question/7238948
