Experimental group B streptococcal infections in mice: hematogenous virulence and mucosal colonization.

A group B streptococcus recovered from a blood specimen from a neonate with sepsis was used to evaluate the use of mice for studies characterizing the hematogenous virulence and the asymptomatic mucosal colonization of the vagina or of the respiratory tract by these bacteria. When injected intravenously, the 50% lethal dose for mice was 10(6); however, as few as 10(2) organisms produced septic deaths. In mice undergoing water diuresis, bacteriuria and pyelonephritis were not produced after direct bladder inoculation of the streptococci. Asymptomatic vaginal colonizations that persisted for 12 days were produced in both pregnant and virgin mice. Vaginal colonization before delivery did not result in transmission of infection to litters or in protection against subsequent oropharyngeal colonization in the suckling mice. In mice born of nonexposed mothers, oropharyngeal colonization was produced in both suckling and 3-week-old weaned mice. Whereas infection persisted for 14 days in all suckling mice, clearance occurred in over 50% of the weaned mice by day 14. The use of mice for studies on the virulence of the group B streptococci as well as for studies on the pathogenesis of disease by virulent strains is discussed.