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Group A carbohydrate (GAC) is a bacterial peptidoglycan-anchored surface rhamnose polysaccharide (RhaPS) that is essential for growth of Streptococcus pyogenes and contributes to its ability to infect the human host. In this study, using molecular and synthetic biology approaches, biochemistry, radiolabeling techniques, and NMR and MS analyses, we examined the role of GacB, encoded in the S. pyogenes GAC gene cluster, in the GAC biosynthesis pathway. We demonstrate that GacB is the first characterized α-D-GlcNAc-β-1,4-L-rhamnosyltransferase that synthesizes the committed step in the biosynthesis of the GAC virulence determinant. Importantly, the substitution of S. pyogenes gacB with the homologous gene from Streptococcus agalactiae (Group B Streptococcus), Streptococcus equi subsp. zooepidemicus (Group C Streptococcus), Streptococcus dysgalactiae subsp. equisimilis (Group G Streptococcus), or Streptococcus mutans complemented the GAC biosynthesis pathway. These results, combined with those from extensive in silico studies, reveal a common phylogenetic origin of the genes required for this priming step in >40 pathogenic species of the Streptococcus genus, including members from the Lancefield Groups B, C, D, E, G, and H. Importantly, this priming step appears to be unique to streptococcal ABC transporter– dependent RhaPS biosynthesis, whereas the Wzx/Wzy-dependent streptococcal capsular polysaccharide pathways instead require an α-D-Glc-β-1,4-L-rhamnosyltransferase. The insights into the RhaPS priming step obtained here open the door to targeting the early steps of the group carbohydrate biosynthesis pathways in species of the Streptococcus genus of high clinical and veterinary importance. © 2019 Zorzoli et al.

Group A carbohydrate (GAC) is a bacterial peptidoglycan-anchored surface rhamnose polysaccharide (RhaPS) that is essential for growth of Streptococcus pyogenes and contributes to its ability to infect the human host. In this study, using molecular and synthetic biology approaches, biochemistry, radiolabeling techniques, and NMR and MS analyses, we examined the role of GacB, encoded in the S. pyogenes GAC gene cluster, in the GAC biosynthesis pathway. We demonstrate that GacB is the first characterized α-d-GlcNAc-β-1,4-l-rhamnosyltransferase that synthesizes the committed step in the biosynthesis of the GAC virulence determinant. Importantly, the substitution of S. pyogenes gacB with the homologous gene from Streptococcus agalactiae (Group B Streptococcus), Streptococcus equi subsp. zooepidemicus (Group C Streptococcus), Streptococcus dysgalactiae subsp. equisimilis (Group G Streptococcus), or Streptococcus mutans complemented the GAC biosynthesis pathway. These results, combined with those from extensive in silico studies, reveal a common phylogenetic origin of the genes required for this priming step in >40 pathogenic species of the Streptococcus genus, including members from the Lancefield Groups B, C, D, E, G, and H. Importantly, this priming step appears to be unique to streptococcal ABC transporter–dependent RhaPS biosynthesis, whereas the Wzx/Wzy-dependent streptococcal capsular polysaccharide pathways instead require an α-d-Glc-β-1,4-l-rhamnosyltransferase. The insights into the RhaPS priming step obtained here open the door to targeting the early steps of the group carbohydrate biosynthesis pathways in species of the Streptococcus genus of high clinical and veterinary importance.

Infection with group B streptococcus (GBS) is a major cause of neonatal illness and death. We examined the antenatal and perinatal risk factors for early-onset GBS disease among neonates.We identified cases by population-based surveillance in all microbiology laboratories serving Alberta. A case was defined as any instance of a positive sterile-site GBS culture in an infant born between 1993 and 1997 who was either less than 7 days old or stillborn after 20 weeks' gestation. We randomly selected controls from a computer-compiled list of all hospital births, including stillbirths after 20 weeks' gestation, in Alberta during the study period. To increase power, we chose 5 or 6 control infants born in the same year as each case infant. We reviewed hospital, prenatal clinic and physician health records and, between 1997 and 1999, conducted maternal interviews by telephone.There were no differences between the 90 cases and 489 controls in sociodemographic variables or in many reproductive and behavioural variables. Case infants were more likely than control infants to be of low birth weight (odds ratio [OR] 3.60, 95% confidence interval [CI] 1.68-7.65), to have been delivered preterm (OR 3.89, 95% CI 2.08-7.27), or to have a mother with amnionitis (OR 15.03, 95% CI 5.58-41.89), intrapartum fever (OR 4.65, 95% CI 2.48-8.69) or premature rupture of the membranes (OR 2.39, 95% CI 1.38-4.14). After adjustment for potential confounders, intrauterine fetal monitoring was associated with a more than 2-fold increase in the risk of neonatal GBS disease (OR 2.24, 95% CI 1.22-4.13).Intrauterine fetal monitoring should be added to the list of risk factors in risk-based screening. Since many of the cases had no identifiable maternal risk factors, universal screening for GBS may be appropriate.