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.
Highlights
Vertical transmission of group B streptococcus (GBS) from a vagina colonized mother to her infant during labor can cause life-threatening infections in newborn
All the eighteen culture positive specimens were positive by the cfb polymerase chain reaction (PCR) assay while only 17 of them were positive by scpB PCR assay
This study showed that PCR using cfb and scpB genes was more sensitive for detection of GSB than the culture method as the rate of detection was 15% by the culture method compared to 23.3 % by cfb PCR assay and 21.7% by scpB PCR
Summary
Vertical transmission of group B streptococcus (GBS) from a vagina colonized mother to her infant during labor can cause life-threatening infections in newborn. Cultures require several days (24–72 h) to yield results, precluding their use for intrapartum screening and these are only performed at 35–37 weeks gestation (Emonet et al, 2013) For this reason, there is a requirement for a rapid diagnostic test to detect GBS colonization status of women in labour, those in preterm labour or women who have not had prenatal care (Gavino and Wang, 2007). New rapid molecularbased tests, such as polymerase chain reaction (PCR), can detect GBS within hours. They have the potential to be used intrapartum and to allow for selective IAP in women carrying GBS (Emonet et al, 2013). The objective of our study was to evaluate PCR targeting cfb and scpB genes as a screening method for detection of maternal colonization of GBS compared to culture
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