Multiplicity of infection
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In microbiology, the multiplicity of infection or MOI is the ratio of agents (e.g. phage or more generally virus, bacteria) to infection targets (e.g. cell). For example, when referring to a group of cells inoculated with virus particles, the MOI is the ratio of the number of virus particles to the number of target cells present in a defined space.[1]
Interpretation
The actual number of viruses or bacteria that will enter any given cell is a stochastic process: some cells may absorb more than one infectious agent, while others may not absorb any. Before determining the multiplicity of infection, it's absolutely necessary to have a well-isolated agent, as crude agents may not produce reliable and reproducible results. The probability that a cell will absorb Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle n} virus particles or bacteria when inoculated with an MOI of Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle m} can be calculated for a given population using a Poisson distribution. This application of Poisson's distribution was applied and described by Ellis and Delbrück.[2]
where Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle m} is the multiplicity of infection or MOI, Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle n} is the number of infectious agents that enter the infection target, and Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle P(n)} is the probability that an infection target (a cell) will get infected by Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle n} infectious agents.
In fact, the infectivity of the virus or bacteria in question will alter this relationship. One way around this is to use a functional definition of infectious particles rather than a strict count, such as a plaque forming unit for viruses.[3]
For example, when an MOI of 1 (1 infectious viral particle per cell) is used to infect a population of cells, the probability that a cell will not get infected is Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle P(0) = 36.79\%} , and the probability that it be infected by a single particle is Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle P(1) = 36.79\%} , by two particles is , by three particles is Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle P(3) = 6.13\%} , and so on.
The average percentage of cells that will become infected as a result of inoculation with a given MOI can be obtained by realizing that it is simply Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle P(n>0) = 1 - P(0)} . Hence, the average fraction of cells that will become infected following an inoculation with an MOI of Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle m} is given by:
- Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle P(n>0) = 1 - P(n=0) = 1 - \frac{m^0 \cdot e^{-m}}{0!} = 1 - e^{-m} }
which is approximately equal to Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle m} for small values of Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle m \ll 1} .
Examples
As the MOI increases, the percentages of cells infected with at least one viral particle also increases.[4]
| MOI | % Infected |
|---|---|
| 1.0 | 63.2% |
| 2.0 | 86.5% |
| 3.0 | 95.0% |
| 4.0 | 98.2% |
| 5.0 | 99.3% |
| 6.0 | 99.8% |
| 7.0 | 99.9% |
| 8.0 | ~100.0% |
See also
References
- ^ Abedon, S. T.; Bartom, E. (2013-01-01), "Multiplicity of Infection", in Maloy, Stanley; Hughes, Kelly (eds.), Brenner's Encyclopedia of Genetics (Second Edition), San Diego: Academic Press, pp. 509–510, ISBN 978-0-08-096156-9, retrieved 2022-03-09
- ^ Ellis, Emory; Delbruck, Max (Jan 20, 1939). "The Growth of Bacteriophage". The Journal of General Physiology. 22 (3): 365–384. doi:10.1085/jgp.22.3.365. PMC 2141994. PMID 19873108.
- ^ "Plaque forming unit". Science Direct.
- ^ Fields BN, Knipe DM, Howley PM (2007). Fields virology: Part 1. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins. ISBN 9780781760607. OCLC 71812790.