Question

please type up the answers.

Conclusions. Questions for further thought and comprehension: 1. What did you determine to be the concentration of the original bacterial culture? Do you think your results are accurate? Explain why or why not. 2. Did you have a countable number of colonies on more than one of your plates? Assume you had two plates that had countable numbers of colonies, one with 124 colonies (and a dilution factor of 1/1.000) and one with 11 colonies (and a dilution factor of 1/10,000). Which of those plates do you think gave you a better concentration estimation of the original bacterial culture? Explain why. 3. You are performing an experiment where you need to determine the concentration of a bacterial culture within 10 minutes. Would you be able to Standard Plate Count to determine the bacterial concentrations for your experiment? Explain why or why not.

Answer 1

1) two ways of determining the bacterial concentration in original culture.

A) spectrophotometer technique in which bacterial count is having direct relation with optical density. More no.of cells then more no. of optical density.

B) Colony counting method or CFU/ ml method- here bacterial culture are diluted with saline and plate on nutrient agar plate and colony will be counted which after multiply with dilution factor give no. Of cells present in culture.

2) here cell counting method was applied and sample was serial diluted upto from 10-1 to 10-4 . 100ul from diluted samples were plated on seperate plate. 1st and 2 nd plate could show very high no. of colonies which could not be countable. But at 3rd and 4th plate which were plated after dilution of factor 10-3 and 10-4 were showed 124 and 11  colonies repectively.

So after mutipling with dilution factor final no. Of cell could be calculated using colony no.of 10-3 plate would be 124x1000x10= 12.5x 105 while from plate with 10-4 dilution would indicates 11x 10000x10= 11x105. So we used to take average no. Of both data to find no. Of cells in culture.But 12.5x105 is more close as more we do dilute more chances of error occur.

C)We cannot used cell plate method if result required in 10in as cell plate required overnight to apper colonies.

For quick result we can use spectrophotometer technique. Here initially fixed no. Of cells were take optical density reading and plot starndard graph using Optical denisty on Y axis with no. Of cells in X axis.

Now, no. Of cells in unknown sample can be find out by k owing it's optical density and putting optical density value in stand curve to find no. Of cells present in this sample.

It's quick method.

Hope it's clear..thanks