Multiplicity of infection

1. Calculation of Multiplicity of
Infection(moi)
Dr. S. Sivasankara Narayani.,M.Sc.,M.Phil.,Ph.D.,MRSB (UK)

2. Multiplicity of infection (moi)
 An experiment with bacteriophage typically begins with an initial period
during which the virus is allowed to adsorb to the host cells.
 It is important to know the ratio of the number of bacteriophages to the
number of cells at this stage of the infection process.
 Too many bacteriophages attaching to an individual cell can cause cell lysis,
even before the infection process can yield progeny virus particles (‘lysis from
without’).
 If too few bacterio phages are used for the infection, it may be difficult to
detect or measure the response being tested.
 The bacteriophage to cell ratio is called the multiplicity of infection (moi).

3. A 0.1 mL aliquot of a bacteriophage stock having a concentration
of 4 X 109 phage/mL is added to 0.5 mL of E. coli cells having a
concentration of 2 X 108 cells/mL. What is the moi?
First, calculate the total number of bacteriophage and the total number of bacteria.
Total number of bacteriophage:
0.1mL X 4x109 phage/ml = 4 X108 bacteriophage
Total number of cells:
0.5mL X 2x108 cells/ml =1 x 108 cells

4. The moi is then calculated as bacteriophage per cell:
moi = 4 x 108 phage / 1x 108 cells
= 4 phage/cell
Therefore, the moi is 4 phage/cell.

5. Reference
 Calculations for molecular biology and Biotechnology – A Guide to mathematics in
the laboratory, Second Edition – Frank. H. Stephenson
11-09-2021
Dr.SS
sivasan91@gmail.com

6. 11-09-2021
Dr.SS