Serial dilutions and isolation methods 1. How I know if the amount of growth on

Question

Serial dilutions and isolation methods 1. How I know if the amount of growth on pour plates werent diluting precise? 2. Explain why in the streak plate the colonies growth extremely minimal Serial dilutions and isolation methods 1. How I know if the amount of growth on pour plates werent diluting precise? 2. Explain why in the streak plate the colonies growth extremely minimal 1. How I know if the amount of growth on pour plates werent diluting precise? 2. Explain why in the streak plate the colonies growth extremely minimal

Explanation / Answer

Answer:

1) For accurate counting in a pour plate technique, the number of colonies per plate should be around 30-300.

To make sure, that the amount of growth on the pour plates is accurate, first perform a series of dilution of the culture and then plate these different dilutions (e.g. 1:10, 1:100, 1:1000....1:100,000). The growth corresponding to each dilution can be calculated by the formula:

bacteria/ml of solution = Number of colonies on plate x dilution factor / volume used for inoculation.

Since different dilutions are used for determining the concentration of microorganisms in starting solution, therefore this method is more precise than the streak plate technique for counting bacteria.

2) In a streak plate technique, while performing a quadrant streak, the first streak will have a heavy growth of microorganism. Second streak will have less growth compared to first streak. In third streak the growth will be even lesser than the second streak and when we perform the fourth streak, then single colonies can be obtained as culture has diluted to a great extent during the fourth subsequent streak. Therefore in a streak plate depending on the number of streaks performed in a quadrant manner, the growth will keep on decreasing with each subsequent streak and final fourth streak will lead to growth of single colonies.

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