Relation between serotype of streptococci of serological group B and growth rate at early logarithmic phase.

Determination of growth rate of streptococci of serological group B at early logarithmic phase by measuring optical density of the growth medium and by measuring the change of conductivity of the culture fluid appeared to be closely related to the serotype of the respective cultures. Most of the human and bovine group B streptococci with type patterns Ia/c, II, III and IV exhibited clearly visible growth of the culture medium after 4 h incubation and changed the conductivity of the culture fluid to a point defined as time to detection within 4 h. No comparable growth could be observed with most of the cultures possessing type antigens R and X, either alone, or in combination with polysaccharide antigens. The importance of type specific capsule sialylation to the growth rate of the bacteria could be additionally shown with two group B streptococci of serotype III and their transposon mutagenized asialo capsular mutants. Both sialylated wild-type group B streptococci grew much quicker than their asialo capsular mutants. The results from additional experiments revealed that the growth velocity seemed to be significantly related to the chain length of the bacteria, to growth patterns of the group B streptococci in fluid media and soft agar and to the surface hydrophobicity of the bacteria. Determination of growth rate at early logarithmic phase could be used to predict various degrees of capsular sialylation of group B streptococci. This might help to understand the pathogenicity of individual group B streptococcal isolates in clinical cases.