However,sometimes a low efficiency of plating merely means that under the conditions used,some virions did not successfully infect cells. Although with bacterial viruses the efficiency of plating is often higher than 50%,with many animal viruses it may be much lower,0.1% or 1% knowledge of plating efficiency is useful in cultivating viruses because it allows one to estimate how concentrated a viral suspension needs to be (that is,its titer)to yield a certain number of plaque