@article{mbs:/content/journal/jgv/10.1099/0022-1317-1-1-71, author = "Breeze, D. C.", title = "Comparative Growth and Selection of Small Plaque and Large Plaque Encephalomyocarditis Virus in the Absence of Inhibitors from Agar", journal= "Journal of General Virology", year = "1967", volume = "1", number = "1", pages = "71-80", doi = "https://doi.org/10.1099/0022-1317-1-1-71", url = "https://www.microbiologyresearch.org/content/journal/jgv/10.1099/0022-1317-1-1-71", publisher = "Microbiology Society", issn = "1465-2099", type = "Journal Article", abstract = "Summary During multicycle growth of clones of encephalomyocarditis (EMC) virus forming large plaques (EMC/r), small-plaque-forming virus (EMC/r+) appeared and was always selected by conditions in the growth medium to become the predominant plaque type. EMC/r arose but was never selected by conditions in the growth medium to predominance in virus pools initiated by EMC/r+ virus clones. Comparison of virus growth showed that EMC/r+ was produced and released from EMC/r+ infected L cells earlier and in 3- to 5-fold higher yields than was EMC/r from L cells infected with EMC/r. Thus, when separately infected cells are considered, selection strongly favoured EMC/r+ progeny. In mixed infection of L cells with EMC/r+ and EMC/r, it was shown that: (1)  Selection favouring the EMC/r+ virus was reduced as the exposed multiplicity/cell of EMC/r+ virus increased from 0·01 to 5·0 p.f.u./cell. (2)  At 1·0 p.f.u./cell EMC/r and 5·0 p.f.u./cell of EMC/r+ less virus of both types was formed in 8 hr than in controls with each virus alone at the same multiplicity. (3)  Eight hr after infection more EMC/r was produced and/or released at 0·01 or 0·1 p.f.u./cell EMC/r and 1·0 or 5·0 p.f.u./cell of EMC/r+, than in control cultures without EMC/r+ virus. ‘ Pure ’ ( > 99 %) pools of the EMC/r virus strain containing 109 to 1010 p.f.u. were produced consistently by increasing the EMC/r virus pool by growth in consecutive single cycle steps, thus eliminating the selective conditions of multicycle growth.", }