Question 8 2 pts A student in microbiology carried out a viable count assay to c

Question

Question 8 2 pts A student in microbiology carried out a viable count assay to count the bacteria in a TS-broth culture of a "pet" bacterium which had been incubated for 24 hours at 30C. To prepare, this student set up several tubes with 9-ml of sterile buffer and labeled these tubes A, B, C, etc. Then the student transferred 1-mL from the bacterial culture into tube A and proceeded with 1:10 dilution steps in series. Finally, the student plated 0.1 mL aliquots from appropriate dilution tubes onto TSA plates After incubation, the student counted 31 colonies on a TSA plate that had been labeled "10%" to reflect all dilution steps (serial dilution and plating). Of the student's lettered serial dilution tubes, how many would have shown turbidity that was visible to the naked eye? (e.g., in other words, contained at least 10,000,000 suspended CFU per mL of buffer?) In the box, type the number of turbid dilution tubes seen in this case.

Explanation / Answer

10-1 ?dilution tube

if the CFU is more than 10,000,000, then the turbidity is observed in the solution. So if 10-7 ?have 37 that means the original sample would have contained 37 * 107 ?cfu per ml. Hence in serial dilution tubes 10-2 ?and 10-1 ?the cfu will be 3700000 and 37000000 respectively. Hence only 10-1? dilution have more than 107?number of cfu hence turbidity will be seen in this tube only.

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