EFFECT OF TYPE-III GROUP-B STREPTOCOCCAL CAPSULAR POLYSACCHARIDE ON INVASION OF RESPIRATORY EPITHELIAL-CELLS

Group B streptococcal (GBS) capsular polysaccharide is an important vi rulence factor, and its role in invasion of cultured respiratory epith elial cells was investigated. A type III GBS clinical isolate, COH1, a nd asialo and unencapsulated isogenic transposon capsule mutants of it were compared in an in vitro invasion assay. The results demonstrated that capsule attenuated the invasion process. Invasion was not affect ed when the A549 epithelial cells were preincubated with purified type III GBS capsular polysaccharide. Polyclonal type III GBS capsule anti body inhibited invasion by COH1 but did not affect invasion by the cap sule mutants. Serotypes Ia, Ib, Ia/c, II, and III all invaded respirat ory epithelial cells but demonstrated some strain variation in magnitu de of invasion. These observations led us to conclude that type III ca psular polysaccharide was not essential for invasion of respiratory ep ithelial cells by GBS and that bacterial factors other than capsule we re responsible for respiratory epithelial cell invasion.