Development of a system for genetic and molecular analysis of Streptococcus agalactiae

DNA-DNA hybridisation was used to compare the genetic relation of human and bovine strains of Streptococcus agalactiae. All strains showed significant homology under very stringent hybridisation conditions. The extent of relatedness did not correlate with the serological type. It was demonstrated that the S faecalis transposon Tn916 could be inserted randomly into the S agalactiae chromosome when introduced by conjugation. The ability of Tn916 insertion to cause genetic changes in S agalactiae was confirmed by identification of a mutation in lactose and trehalose fermentation associated with acquisition of the transposon. This system should be useful in genetic analysis of the pathogenicity of S agalactiae.