DETECTION OF MATERNAL COLONIZATION OF GROUP B STREPTOCOCCUS BY PCR TARGETING Cfb AND ScpB GENES

Abstract

Group B Streptococcus (GBS) is a leading cause of neonatal morbidity and mortality. Molecular based tests, such as polymerase chain reaction (PCR), can detect GBS within hours and can be used intrapartum allowing for selective intrapartum antibiotic prophylaxis (IAP) in women carrying GBS. The aim of this work was to evaluate PCR as a rapid screening method for detection of maternal colonization of GBS compared to culture. Vaginal/rectal swabs were collected from 120 pregnant women at 35-37 weeks of gestation and cultured on CNA medium. GBS was identified by gram staining and catalase, hippurate and CAMP tests and confirmed by latex agglutination for GBS antigens. PCR was done using two assays; one targeting the cfb gene and the other targeting the scpB gene. Results revealed thatGBS colonization was detected in 15%, 23.3% and 21.7% of pregnant women by culture, cfb PCR assay and scpB PCR assay respectively. cfb PCR assay showed 100% sensitivity and 90.2% specificity whereas scpB PCR assay showed 94.4% sensitivity and 91.2% specificity. PCR could detect GBS genome at a concentration of as low as 10-2 for cfb PCR and 10-3 for scpB PCR. In conclusion, PCR is a rapid, specific and sensitive tool for detection of maternal colonization of GBS. PCR assay targeting scpB gene is more sensitive than that targeting cfb gene.