# Improved detection of group B Streptococcus in rectovaginal samples of pregnant individuals in Brazil using chromogenic medium

## TL;DR

A new method using chromogenic media improves the detection of Group B Streptococcus in pregnant individuals in Brazil, offering a faster and more cost-effective alternative to traditional methods.

## Contribution

The study demonstrates that chromogenic media outperforms traditional methods in detecting GBS in low-resource settings.

## Key findings

- Chromogenic media detected significantly more GBS-positive samples than traditional broth methods.
- The chromogenic method was faster, more cost-effective, and inhibited contaminant microbiota better.
- However, it failed to detect GBS in samples with low bacterial density.

## Abstract

Universal screening of pregnant individuals followed by intrapartum antibiotic prophylaxis is the most effective approach to prevent group B Streptococcus (GBS) neonatal infections. Traditional protocols for GBS detection in rectovaginal samples involve a pre-enrichment step using selective broth, followed by inoculation onto blood agar, but these methods can be labor-intensive, time-consuming, and costly in low-resource settings. Here, we compared the performance of conventional selective broth prior to plating (THB-NAG) with direct plating onto chromogenic media (CA) for GBS detection among 1,128 pregnant individuals in Brazil. Overall, GBS was detected in 7.8% (88) of samples. CA detected a significantly (P < 0.0001) higher number of positive samples (6.5%; 73) when compared to THB-NAG (2.7%; 31). CA was also superior in inhibiting contaminant microbiota, was faster and more cost-effective, and showed high sensitivity and accuracy levels when compared to THB-NAG, although it had failed when samples had low GBS density. Adopting more feasible and cost-effective protocols, such as the CA method shown in this study, can lead to improved adhesion to the universal antenatal GBS screening and thus, to the prevention of early GBS disease in low-resource settings, such as Brazil.

Group B Streptococcus (GBS) is a leading cause of life-threatening neonatal infections. The recommended strategy to prevent GBS disease is based on GBS screening of pregnant individuals, followed by antibiotic prophylaxis. However, the standard laboratory method for GBS detection requires extended incubation time and may present challenges associated with costs and feasibility, making it difficult for routine implementation in low-resource settings. Additionally, the overgrowth of accompanying microbiota can hinder GBS detection, potentially reducing the method’s sensitivity. This creates barriers to effective prevention strategies. In this context, chromogenic media have emerged as a promising alternative, offering faster, simpler, and more accurate detection through color-based differentiation of colonies. However, this method has not been fully evaluated in local healthcare conditions in countries like Brazil. This study was undertaken to investigate whether chromogenic media could provide a more practical, affordable, and reliable option for GBS detection in routine prenatal care.