Detection of Streptococcus agalactiae by immunochromatography with group B streptococcus-specific surface immunogenic...

Infection with Streptococcus agalactiae (Group B streptococcus: GBS) is a significant cause of morbidity and mortality in neonates. Screening for GBS is mainly done by culture-based methods, but a reliable result may take several days to obtain and culture is difficult to perform at institutions without a laboratory. We evaluated an immunochromatography method for rapid detection of GBS-specific surface immunogenic protein (Sip) using anti-Sip monoclonal antibodies.

A total of 377 cervical and vaginal swabs collected during weeks 35-37 of gestation were inoculated into GBS medium F and incubated. Growth of microorganisms and production of red/orange pigment were assessed by observation. Then culture extracts were subjected to immunochromatography and were also inoculated onto chromID Strepto B (STRB) medium, after which isolates were serotyped and characterized by PCR.

Of the 377 samples, 54 (14.3%) were positive for GBS by immunochromatography after incubation in GBS medium F. On the other hand, GBS was isolated from 58 (15.4%) of the 377 samples by culture with GBS medium F and STRB medium. Ten of the 58 isolates were non-pigmented and 4 of these were not detected by immunochromatography. The sensitivity, specificity, positive predictive value, and negative predictive value of immunochromatography were 93.1% (54/58), 100% (319/319), 100% (54/54), and 98.8% (319/323), respectively.

Immunochromatography was comparable to culture on STRB medium for detecting GBS, indicating that this method could be used clinically for GBS screening in pregnant women even at small institutions.