Serial passage

Serial passage refers to the process of growing bacteria or a virus in iterations. For instance, a virus may be grown in one environment, and then part of that virus can be removed and put into a new environment. This process is repeated with as many stages as desired, and then the final product is studied, often in comparison with the original virus.

This sort of facilitated transmission is often conducted in a laboratory setting, because it is interesting to observe how the virus or bacterium that is being passed evolves over the course of an experiment. In particular, serial passage can be quite useful in experiments that seek to change the virulence of a virus or other pathogen. One consequence of this is that serial passage is useful in creating vaccines, since scientists can apply serial passage and create a strain of virus that has low virulence.

Serial passage can either be performed in vitro or in vivo. In the in vitro method, a virus or a strain of bacteria will be isolated and allowed to grow for a period of time. After the sample has grown for some time, part of it will be transferred to a new environment and allowed to grow for the same period of time. This process will be repeated as many times as desired.

Alternatively, an in vivo experiment can be performed where an animal is infected with a pathogen, and this pathogen allowed time to grow in that host before a sample of it is removed from the host and passed to another host. This process is repeated for a certain number of hosts; this number is determined by the individual experiment.

When serial passage is performed either in vitro or in vivo, the virus or bacterium that is being manipulated may evolve by mutating repeatedly.

Identifying and studying mutations that occur through serial passage often reveals information about the virus or bacterium being studied. Accordingly, after serial passage has been performed it can be valuable to compare the resulting virus or sample of bacteria to the original, noting any mutations that have occurred and what the collective effect of these mutations is. A variety of significant outcomes are possible. The virulence of the virus may be changed, for example, or a virus could evolve to become adapted to a different host environment than that in which it is typically found. Notice that relatively few passages are necessary to produce a noticeable change in a virus; for instance, a virus can typically adapt to a new host within ten or so passages.

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Wikipedia