ISOLATION OF A SERIES OF MENGO VIRUS VARIANTS DIFFERING IN SENSITIVITY TO POLYANIONS

Abstract

The isolation of six distinct new plaque variants from pools of S- and M-Mengo (small- and medium-plaque variants respectively) is described. The size of plaques produced in L cell monolayers under nutrient agar by five of the six new variants is strongly inhibited by the addition to the overlay of dextran sulfate of molecular weight 500,000. The sixth, although similar to L-Mengo in its virulence to mice and in having plaques that are almost unaffected by the addition of protamine or dextran sulfate to the overlay, can be distinguished from the latter by the larger and more uniform plaques it produces. The marked heterogeneity in the size of plaques produced by L-Mengo appears to be an inherent property of this variant, since all attempts to isolate other plaque variants from L-Mengo pools have been unsuccessful.The intraperitoneal LD₅₀'s of all six new variants in 14- to 16-g mice was determined. There is no complete correlation between the virulence of these variants and their sensitivity to inhibition by dextran sulfate.