[Experimental mouse models of susceptible and resistant pneumococcal pneumonia with special reference to the cause of bacteremia].

To study the pathogenesis of Streptococcus pneumonieae, we established mouse models with acute pneumonia caused by the penicillin susceptible S. pneumoniae strain (J4) and the clinically isolated penicillin resistant S. pneumoniae (RSTY045). The MICs of the J4 and RSTY045 strain against penicillin G were 0.016 and 2.0 micrograms/ml, respectively. In the therapeutic experiment, the ED50 of penicillin G against the J4 strain was 14,800 IU/kg and that of the RSTY045 strain was 92,000 IU/kg. In the pathological study, both lungs infected with J4 and RSTY045 showed typical bacterial pneumonia. The pathogen infected with the J4 strain showed septic pneumonia in which neutrophils were more invasive to the vascular area than that infected with RSTY045. All of the J4 strain blood cultures tested positive 24 hours into the pneumonia course, whereas only two of the RSTY045 strains showed positive at the end of the pneumonia course. The pneumolysins of J4 and RSTY045 were 191 HU/ml and 1,622 HU/ml respectively. There seemed to be no association between pneumolysin and the blood culture results in our model. To investigate these results, we infected mice with four PSSP and six PRSP clinically isolated strains (RSTY strains) containing J4 and RSTY045, respectively. Blood cultures were performed at 24 hours and 3 days after infection and death rates were calculated 3 days after infection. In the PSSP infection groups, 81.7% showed a positive result at 24 hours and 100% at 3 days after infection showed positive results, whereas in the PRSP 40.0% at 24 hours and 59.0% at 3 days after infection. The average levels of pneumolysin in PSSP and PRSP were 473.0 HU/ml and 835.2 HU/ml, respectively. There seemed to be no association between pneumolysin, death rates and the of blood culture results. (p > 0.05).