Analysis of restriction fragment length polymorphisms of the insertion sequence IS1381 in group B Streptococci.

Group B streptococci (GBS) are typed by capsular polysaccharide type. IS1381, an insertion sequence previously described in Streptococcus pneumoniae, was cloned from GBS strain A909. The presence of multiple copies of IS1381 in A909 suggested that IS1381 analysis might be an effective subtyping tool. IS1381 was found by Southern blot analysis to be present in 18 (72%) of 25 of unrelated GBS isolates tested. IS1381 analysis allowed discrimination between strains that contain IS1381 with a discriminatory power >99%. Eight of 8 sets of epidemiologically related isolates containing IS1381 give identical or nearly identical patterns of IS1381 insertion. For 2 maternal/infant sets, a single additional insertion was seen in 1 strain, suggesting that an additional insertion occurred between maternal colonization and infection of the infant. Insertion patterns of IS1381 are an effective tool for subtyping GBS.