Effect of exposure to the atmosphere on the infectivity of group A streptococci.

During exposure to the atmosphere, type 14 group A streptococci lost infectivity for mice more rapidly than they declined in viability. The loss of infectivity resulted from phenotypic, not genotypic, changes. Comparison of rates of loss of infectivity during exposure of capsulated and noncapsulated streptococci suggested that the principal effect of atmospheric exposure was on the capsule, a known determinant of infectivity. Accelerated drying promoted the loss of infectivity.