Comparative Molecular and Microbiologic Diagnosis of Vaginal Colonization by Group B Streptococcus in Pregnant Women during Labor

Abstract

Objective(s) Rapid tests for detection of Streptococcus agalactiae or Group B Streptococci (GBS) at the onset of labor are needed to permit early intrapartum antibiotic prophylaxis. This study aimed to evaluate the PCR assays targeting the 16S ribosomal RNA gene (16S rDNA) for detection of the GBS in comparison with a specific culture method. Materials and Methods Two swabs were used to obtain vaginal specimens from the 330 pregnant women attended delivery room at Hedayat hospital, Tehran, Iran. One swab was analyzed by direct plating onto selective GBS agar medium (ISLAM) and the other swab was used for a PCR assay, which amplified the 16S rDNA of S. agalactiae. Comparative study between the selective culture and the PCR assay was done among the 330 tested women. Results The GBS colonization rate based on the culture results was 20.6% (68/330). Both culture and PCR methods were positive for 56 and negative for 253 women. The culture method was positive and PCR was negative in 12 women. The culture was negative and the PCR positive for 9 women. Sensitivity of the PCR assay was 82.3% and specificity was 96.5%. The positive predictive value was 86.15% and negative predictive value was 95.4%. Conclusion ISLAM diagnostic procedure and PCR are rapid and reliable analyzing methods, which might be useful for accurate diagnosis of GBS colonization in pregnant women at the time of delivery.