Temperature-Sensitive Mutants of Type I Streptococcus pneumoniae: Preparation, Characterization, and Evidence for Attenuation and Immunogenicity

Thirteen temperature-sensitive (ts) mutants of type I Streptococcus pneumoniae were selected after exposure of virulent wild-type (ts+) organisms to nitrosoguanidine. Each mutant resembled the ts+ parent in properties of α-hemolysis, bile solubility, optochin sensitivity, antibiotic sensitivity, and serotype. Unlike the ts+ parent, however, each ts mutant was restricted in its capacity to form colonies on blood agar at 38 C. With the exception of two mutants, there was a correlation between the degree of temperature-sensitivity of a mutant and its genetic stability. When inoculated intraperitoneally into mice, 11 of 13 mutants were attenuated and induced homologous resistance. Three mutants (ts 1, ts 3, and ts 4) were also studied in hamsters and were found to be attenuated and immunogenic after intraperitoneal injection. Study of the behavior of mutants ts 1, ts 3, and ts 4 in the blood of hamsters suggested that attenuation may be related, in part, to decreased growth and survival of ts organisms at body temperature. Mutants ts 1 and ts 4 were completely attenuated for hamsters when administered intranasally and induced significant resistance to subsequent challenge with wild-type organisms by the same route. Local administration of ts mutants of type I S. pneumoniae to hamsters may provide a model for evaluating the potential of live vaccines in the prevention of disease due to bacterial respiratory tract pathogens.