Performance of a new DNA probe for the detection of group B streptococcal colonization of the genital tract

Abstract

OBJECTIVE: To test the performance characteristics of a new DNA probe designed for the rapid identification of heavy colonization of the genital tract with group B streptococci. METHODS: Vaginal and combined vaginal-perianal samples were collected from 193 pregnant women and cultured on colistin-nalidixic acid agar plates. Bacterial growth was classified semiquantitatively. Specimens were also tested by a new DNA probe in two formats: a direct assay performed on the swabs soon after collection and an assay performed after the swabs were incubated for 24 hours in an enriched culture medium. RESULTS: The agar cultures were positive in 36 of 193 patients (18.6%, 95% confidence interval 13.2-24). Nineteen women were lightly colonized, and 17 were heavily colonized (at least 10(4) colonies/mL). The combined vaginal-perianal swabs yielded positive results more often than the vaginal swabs alone (26 versus 16, chi 2 = 24, P < .01). In its direct form, the assay had only 8.3% sensitivity in identifying colonized women. In heavily colonized women, the sensitivity of the assay increased slightly to 12%. After a 16-24-hour incubation, the sensitivity of the assay was 81%. CONCLUSION: The direct assay is insufficiently sensitive for clinical use. The delayed assay offers no advantage over standard cultures.