TCID50 MOI PFU意义及其换算

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Multiplicity of infection (MOI)

The multiplicity of infection (abbreviated MOI) is the average number of

phage per bacterium. The MOI is determined by simply dividing the

number of phage added (ml added x PFU/ml) by the number of bacteria

added (ml added x cells/ml). The average number of phage per bacterium

in the population could be 0.1, 1, 2, 10, etc, depending upon how you set

up the experiment.

Although the MOI tells you the average number of phage per bacterium,

the actual number of phage that infect any given bacterial cell is a

statistical function. For example, if the MOI is 1, some cells will get

infected with one phage but some cells may be infected with 0 phage and

other cells infected with two phage. The proportion of cells in a

population infected by a specific number of phage (n) can be calculated

from the Poisson distribution.

PFU:plaque forming unit，空斑形成单位。感染性滴度的单位一般表示

为PFU/ml。由于测定pfu往往重复性较差，因此近些年许多研究又

开始采用TCID50方法来计算病毒的感染单位。因此建议也可使用

TCID50法。

MOI :multiplicity of infection，感染复数。传统的MOI概念起源于噬

菌体感染细菌的研究。其含义是感染时噬菌体与细菌的数量比值，也

就是平均每个细菌感染噬菌体的数量。噬菌体的数量单位为pfu。一

般认为MOI是一个比值，没有单位，其实其隐含的单位是pfu

number/cell。后来MOI被普遍用于病毒感染细胞的研究中，含义是

感染时病毒与细胞数量的比值。

然而，由于病毒的数量单位有不同的表示方式，从而使MOI产生了

不同的含义。能产生细胞裂解效应的病毒例如单纯疱疹病毒等习惯上

仍用pfu表示病毒数量，因此其MOI的含义与传统的概念相同。

传统意义上的MOI的测定，其原理是基于病毒感染细胞是一种随机

事件，遵循Poisson分布规律，可计算出感染一定比例的培养细胞所

需的感染复数（MOI）。其公式为：

P = 1- P(0) ,P(0) = e-m 或m = -InP（0）。

其中：

P 为被感染细胞的百分率

P(0)为未被感染细胞的百分率

m为MOI值

例如，如果要感染培养皿中99%的培养细胞，则：

P(0) = 1% = 0.01

m = -In(0.01)= 4.6 pfu/cell。

TCID50 Protocol：

1：制备96孔板单层细胞

2：将病毒做系列稀释，横向接种单层细胞板，每稀释度重复3孔

3：每日观察细胞病变，记录高于50和低于50％病变孔的病毒稀释

度，

4：计算比距，获得TCID50

计算比距：

（高于50％的病变率－50％）（高于/50％病变率－小于50％病变率）

＝比距；

比距与接近50%病变率的病毒的稀释度的指数相加，就获得了指数。

比如：比色计算或者显微镜观察病毒的TCID50在10的负7和8次

方之间，那么，指数－8与比距相加，获得的新的指数，就是TCID50

的指数，TCID50=10的-7.几次方

TCID50与 PFU换算:

PFUs＝0.7×TCID50的滴度

/biovirus/blog/item/

MOI（感染复数）TCID50 PFU 病毒的滴度，感染单位

2010-06-19 19:40

Q: The author infected cells with an M.O.I of 50. The virus I titrated is 5X10(7)p.f.u/ml. So how

much virus should I dilute to get an M.O.I of 5?

A: An MOI of 50 means 50 active viral particles per cell. So, if you have 10(6) cells on a plate x

MOI (50)= 5x10(7) p.f.u for that plate (which equals one ml of your virus stock).

The number of p.f.u./ml was then calculated as TCID50 /ml x 0.69.

/cgi/content/abstract/90/10/2364

Ian J. Groves,3 Matthew B. Reeves4 and John H. Sinclair. Lytic infection of permissive cells with

human cytomegalovirus is regulated by an intrinsic „preimmediate-early‟ repression of viral gene

expression mediated by histone post-translational modification. Journal of General Virology

(2009), 90, 2364–2374

Converting TCID[50] to MOI

How do I convert TCID[50] to MOI?

The easiest way to convert TCID[50] to an MOI value is to do the following:

Convert the titer by TCID[50] to plaque forming units (PFU). To do this, multiply the

titer by 0.7.

Since plaque forming units represents the estimated number of infectious units per

volume of virus material, one can estimate the total number of infectous particles.

Next, divide the number of infectious particles by the number of cells to be infected to

obtain the MOI. Then, dilute the virus accordingly in order to obtain 0.1 to 0.01 MOI.

For example,

If the TCID[50] titer for a given virus is 10(7.25) TCID[50] per 0.2 ml, 10(7.25) is

approximately 17,782,794 (the inverse log of 7.25), and when multiplied by 0.7 gives

12,447,956 PFU per 0.2 ml. If you were going to infect 10 million cells at an MOI of

0.1, you need 1,000,000 infectious particles. For the above example, you should dilute

0.2 ml of the virus stock at least 1:12.5 to obtain 1,000,000 infectious particles per 0.2

ml, then this volume (0.2 ml x 12.5 = 2.5 ml) should be diluted appropriately to infect

the number of vessels. (Usually we infect a 75 cm2 flask with 2 mL of diluted virus or

a 150 cm2 flask with 5 mL of diluted virus).

为什么病毒载体的感染单位有不同的表示方法？

不同的病毒载体，其表示感染单位的方式有所不同。

早期的逆转录病毒载体一般用CFU，是“clone forming unit”的简称，叫做“克隆形成单位”。感染性滴度的单位一般表示为CFU/ml。这是因为最早的

逆转录病毒系统是Dr. Dusty Miller建立的LN系列（包括LN，LXSN，LNSX，LXCN，LNCX等），包装细胞株是PA317, psi2，G&P86等。在这

套载体中N代表了neo基因，X代表外源基因，S代表SV40启动子，C代表CMV启动子，L代表逆转录病毒的LTR，具有启动子功能。因此，

早期的LN系列载体是双表达载体，重组病毒中有neo基因的表达单位，滴度测定时用病毒感染NIH3T3细胞，用G418选择培养，根据形成neo

基因抗性克隆的多少来计算病毒滴度，因此滴度的单位就用cfu/ml来表示了。这种表示方法至今还很常用。

腺病毒载体的感染单位一般用PFU表示，是“plaque forming unit”的简称，叫做“空斑形成单位”。感染性滴度的单位一般表示为PFU/ml。由于测定

pfu往往重复性较差，因此近些年许多研究又开始采用古老的TCID50方法来计算腺病毒的感染单位。

What do MOI and PFU mean?

The term MOI stands for Multiplicity Of Infection. This value describes the ratio of the number of virions per target cell at the time the virus is added to the

cuture.

The term PFU stands for Plaque Forming Unit. One PFU/ml is defined as 1 lytic event (seen as a plaque on a lawn of 293 cells) per milliliter of media. This is

a measure of viral titer.

Additional information can be found in the following reference: Nature Medicine, vol. 3, number 7, July 1997. Sensitivity and Reproducibility in Adenoviral

Infectious Titer Determination. Once the viral titer is determined, a given MOI can be specified and used for the target cells.

什么是MOI？

MOI 是multiplicity of infection的缩写，中文译为感染复数。传统的MOI概念起源于噬菌体感染细菌的研

究。其含义是感染时噬菌体与细菌的数量比值，也就是平均每个细菌感染噬菌体的数量。噬菌体的数量单

位为pfu。一般认为MOI是一个比值，没有单位，其实其隐含的单位是pfu number/cell。后来MOI被普遍

用于病毒感染细胞的研究中，含义是感染时病毒与细胞数量的比值。

然而，由于病毒的数量单位有不同的表示方式，从而使MOI产生了不同的含义。能产生细胞裂解效应的病

毒例如腺病毒、单纯疱疹病毒等习惯上仍用pfu表示病毒数量，因此其MOI的含义与传统的概念相同。而

对于某些病毒如AAV病毒，无法用pfu表示病毒的数量，而是采用TU、IU、病毒颗粒（viral particles, v.p）

或基因组数量（vector ）来表示病毒数量，因此其MOI就有了不同含义。采用TU或IU，MOI

的含义便是TU number/cell 或IU number/cell。采用v.p.，MOI的含义便是v.p. number/cell 。采用v.g，MOI

的含义便是v.g. number/cell。

可以将上述不同的MOI 表示方式分为2种：

1） 以活性单位表示病毒数量，如pfu, TU, IU。这时MOI的含义是指平均每个细胞感染病毒的活性单位数。

2） 以病毒颗粒或基因组数表示病毒数量，如v.p. 或v.g. 。这时MOI的含义是指平均每个细胞感染病毒

的病毒颗粒或基因组数。

值得一提的是，上述2种不同的MOI 表示方式在含义和数值上都有所不同。前一种是传统意义上的MOI，

后一种MOI表示方式的含义更为简化和直观，也逐步被一些研究者采用。

传统意义上的MOI的测定，其原理是基于病毒感染细胞是一种随机事件，遵循Poisson分布规律，可计算

出感染一定比例的培养细胞所需的感染复数（MOI）。其公式为：

P(k) = 1- P(0) ,P(0) = e-m 或m = -InP（0）。

其中：

P(k) 为被感染细胞的百分率

P(0)为未被感染细胞的百分率

m为MOI值

例如，如果要感染培养皿中99%的培养细胞，则：

P(0) = 1% = 0.01

m = -In(0.01)= 4.6 pfu/cell。

由此可以看出，由于病毒特性和研究者习惯的不同，MOI的单位由原来约定俗成的

pfu number/cell变成多种表示单位。在阅读文献和写作论文时，应注意MOI的具体含义和单位。

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PFU: plaque forming units A measure of the biological activity of a virus

sample.

MOI: multiplicity of infection MOI= #PFU/cell eg. If 1X106 cells

are infected with 5X106 PFU, the MOI is calculated as 5X106/1X106=5

CPE: cytopathic effect

The Poisson distribution is used to calculate the proportion (P) of cells

infected with K (0, 1, 2, 3, etc.) PFU when virus is added to cells at a

particular MOI (m).

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Sample problem:

You infect a monolayer of 1X107 cells with 0.1 ml. of a sample of virus the

titer of which is 1X 109 PFU/ml.

What is the MOI of this infection, and how many cells are infected?

0.1ml. ( 1 X 109 PFU/ml ) = 1 X 108 PFU

MOI = PFU/cell =1 X 108 / 1 X 107 =10

The proportion of infected cells = 1- the proportion of uninfected cells =

1-e-m =1-e-10 =0.999952

The number of infected cells = the total number of cells multiplied by the

proportion of infected cells = (1X107) (0.999952) = 0.999952X107. Thus at

an MOI of 10, most cells are infected.

Now you calculate the number of cells that are uninfected, infected with one

PFU, and multiply infected.

The One-step growth curve was devised by Ellis and Delbruck to study the single cell life cycle of bacteriophage.

The key element of this experiment is synchronization of the infected cells so that the population reflects events

occurring in the single cells. Synchronization is achieved by infecting the culture of cells at an MOI at which most

of the cells are infected (MOI of 5-10). At various times aliquots of the infected culture are withdrawn and assayed

for PFU by plaque assay. Samples can be tittered directly, or lysed prior to analysis to observe intracellular events.

Refer to your text for a graphic plot of the curves. Pay special attention to the events in the life cycle of a virus (eg.

Adsorption, uncoating, biosynthesis, assemble, release) that occur in the latent, eclipse, exponential rise, and

plateau regions of the curve. From the total number of cells in the culture, and the total number of progeny PFU

produced at the end of the rise (“burst”) one can calculate the number of PFU produced per cell.