[Virulence of Streptococcus pneumoniae strains isolated in acute and chronic inflammatory lung diseases].

The virulence of 139 Str. pneumoniae strains was studied. The cultures differing in virulence were found to have the same specific prominence. In most serotypes the LD50 for mice was within greater than 3-5 lg/ml and greater than or equal to 6 lg/ml. Highly virulent cultures comprised a comparatively small number of serotypes. More than half of pneumococcal strains isolated in acute pneumonia possessed the moderate level of pathogenicity for white mice. During the acute phase of inflammatory pulmonary diseases Str. pneumoniae strains with high and moderate virulence prevailed, and at the period of clinical remission those with low virulence.