VIRULENCE OF STREPTOCOCCUS-SUIS TYPE-2 FOR MICE AND PIGS APPEARED HOST-SPECIFIC

A murine model for Streptococcus suis infection in pigs was validated by inoculating groups of 5 BALB/c and 5 CF1 mice with 10(7) CFU/ml of 13 different S. suis serotype 2 strains. The pathogenicity of these st rains had been established in a standardized pig model of S. suis infe ction using one-week-old gnotobiotic pigs. We inoculated groups of mic e intraperitoneally with 4 strains that were highly virulent for pigs and belonged to the phenotype MRP+EF+, with 4 strains, that were weakl y virulent for pigs and belonged to the phenotype MRP+EF, and with 5 strains that were non-virulent for pigs and belonged to phenotype MRP- EF-. The S. suis strains that were highly virulent for pigs caused hig h morbidity and an intermediate mortality in mice, the S. suis strains that were weakly virulent for pigs caused high morbidity but low mort ality, and the strains that were non-virulent for pigs, induced highes t morbidity and mortality. These results were comparable in both breed s of mice. In contrast to the pathology of S. suis infection in pigs w ith specific lesions, lesions in mice were histologically often charac terized as non-specific, i.e., necrotizing encephalitis and focal or d iffuse hepatitis sometimes with abscesses. Irrespective of breed (BALB /c vs. CF1), the murine model used for S. suis infection was incompati ble with the pig model. This indicates that virulence of S. suis type 2 for mice and pigs is host-specific. Therefore, we regard the present ly available murine models unsuitable for studying S. suis infections in pigs. (C) 1997 Elsevier Science B.V.