The growth of the HPV was monitored as follows: 10 9 cells and 10 6 viruses in o
ID: 64957 • Letter: T
Question
The growth of the HPV was monitored as follows: 109 cells and 106 viruses in one milliliter were incubated under appropriate conditions. Following a first infectious cycle, a direct count and a plaque assay were performed. In the case of the direct count, the mixture was diluted by a factor of 1 000X after which beads were added to obtain a final concentration of 1 X 104 beads/mL. A microscopic field of vision revealed 20 beads and 150 virions. In the case of the plaque assay, 67 plaques were observed on a plate on which 0.1 mL of a 10-5 dilution was assayed.
1. According to the direct count, what was the volume observed in a field of vision?
2. According to the direct count, what was the number of virus/mL after the first infectious cycle?
Explanation / Answer
According to the direct count, 20 beads revealed 150 virions. Therefore, the number of virions on 104 beads, which were diluted by a factor of 103 x is:
Multiplicity of infection = number of virions detected/number of cells infected
=
From the plaque assay, the number of plaques observed are 67, in 0.1 ml. Therefore, in 1ml, the number of plaques are 670. The dilution factor used is 10-5. Therefore, the number of plaques for original dilution is 6.70 ×107
Multiplicity of infection (MOI) =
This means, the average number of virus particles infecting each cell is 0.075 or 0.0675, according to the calculation.
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