Replication-associated increase in numbers of replication-competent phage genomes.
In broth media phage population growth can result, ultimately, in infection of a majority of co-cultured phage-susceptible bacteria. Such an outcome is not a necessary consequence of phage population growth, however, since there exists a distinction between increases in virion numbers and increases in virion numbers to the point where encounter with most bacteria within a culture is likely.
In agar-based media, phage population growth can be seen as phage plaque formation. Here a substantial fraction of phage-susceptible bacteria can become phage infected because constraints on phage diffusion can result in phage concentration, in the course of population growth, to densities that indeed are capable of resulting in substantial bacterial eradication, at least locally.
Note that phage population growth need not result in increases in virion number. One, in fact, can distinguish phage population growth into what can be described as bacteria-like, as displayed by prophages, and virion-like, as displayed in the course of productive phage infections.
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