PLAQUE CHARACTERISTICS OF COXSACKIE A7 VIRUS

Abstract

Conditions for the production of plaques by cytopathogenic strains of coxsackie A 7 (CA 7) virus were examined, and plaque characteristics and biological properties of the virus strains were studied. Out of 14 strains of CA 7 virus, AB-IV-KH and two lines of the prototype strains showed remarkable heterogeneity in size of plaques in monkey kidney cells, while the other strains produced uniform, small plaques only. An appropriate concentration of DEAE-dextran or protamine sulfate in the agar overlay enhanced significantly the formation of plaques by these strains, especially of small plaques, and the concentration of sodium bicarbonate in the agar overlay was also proved to be one of the important factors affecting the plaque formation of the virus. A large plaqueforming (LP) and a small plaqueforming (SP) viruses were obtained from AB-IV-KH strain by serial plaque purifications or terminal dilution passages. LP virus was genetically less stable than SP virus, and plaque production of SP virus was significantly enhanced by DEAE-dextran or protamine sulfate and reversely inhibited by agar extract or sulfated polysaccharides. No differences in growth rate in monkey kidney cell cultures, serological property or pathogenicity in suckling mice were observed between LP and SP viruses.