Colonisation of the upper respiratory tract of mice with group B streptococci type III with reference to the R-protein.

Nine strains of group B streptococci type III, five with R-protein (R+) and four without (R-) were tested for capacity to colonise the upper respiratory tract in mice and to adhere to human buccal cells. In the mouse model, 80-microliter inocula of dilutions of overnight cultures of the strains in Todd Hewitt broth were placed in the external nares under light ether anaesthesia. A pilot experiment demonstrated that it was reasonable to study the throat colonisation 2 and 4 days after inoculation. Groups of 18-20 mice were then given inocula containing 8 X 10(6) cfu/ml of five R+ and four R- strains. At day 4, significantly more mice were colonised with type III, R+ strains (73% of the animals) than with type III, R- strains (44%) (p less than 0.01). In adherence experiments with human buccal cells, no difference was found between the R+ and R- strains. The results indicated that the higher colonisation rate among R+ strains was mediated by mechanisms other than adherence.