The Double Life of Group B Streptococcus: Asymptomatic Colonizer and Potent Pathogen

Abstract

Group B Streptococcus (GBS) is a β-hemolytic Gram-positive bacterium that colonizes the lower genital tract of approximately 18% of women globally as an asymptomatic member of the gastrointestinal and/or vaginal flora. If established in other host niches, however, GBS is highly pathogenic. During pregnancy, ascending GBS infection from the vagina to the intrauterine space is associated with preterm birth, stillbirth, and fetal injury. In addition, vertical transmission of GBS during or after birth results in life-threatening neonatal infections, including pneumonia, sepsis, and meningitis. Although the mechanisms by which GBS traffics from the lower genital tract to vulnerable host niches are not well understood, recent advances have revealed that many of the same bacterial factors that promote asymptomatic vaginal carriage also facilitate dissemination and virulence. Further, highly pathogenic GBS strains have acquired unique factors that enhance survival in invasive niches. Several host factors also exist that either subdue GBS upon vaginal colonization or alternatively permit invasive infection. This review summarizes the GBS and host factors involved in GBS's state as both an asymptomatic colonizer and invasive pathogen. Gaining a better understanding of these mechanisms is key to overcoming the challenges associated with vaccine development and identification of novel strategies to mitigate GBS virulence.

Temporal development of the infant gut microbiome

“…Fifty per cent of all pregnant women will carry GBS at some point over the course of their pregnancy. While healthy pregnant women are typically asymptomatic, GBS infections in fetuses or infants are detrimental [33]. GBS is associated with preterm birth and infant mortality, and is a major cause of sepsis, pneumonia, meningitis and bacteraemia [33,34].…”

“…While healthy pregnant women are typically asymptomatic, GBS infections in fetuses or infants are detrimental [33]. GBS is associated with preterm birth and infant mortality, and is a major cause of sepsis, pneumonia, meningitis and bacteraemia [33,34]. Additionally, there is a correlation between the timeline of antibiotic administration prior to vaginal delivery and the infant's microbiome make-up, with a decrease in Bifidobacterium and an increase in Clostridium [35].…”

In silico Prediction of New Drug Candidates Against the Multidrug-Resistant and Potentially Zoonotic Fish Pathogen Serotype III Streptococcus agalactiae

“…Streptococcus agalactiae is a multi-host, invasive, Gram-positive pathogen, identified in several species of terrestrial and aquatic mammals, reptiles, amphibians, and fish ( Delannoy et al, 2013 ). It is a commensal organism of the human gastrointestinal and lower genital tracts, with the potential to cause diseases mainly in newborns, elderly, and individuals with underlying medical conditions ( Armistead et al, 2019 ; Raabe and Shane, 2019 ). Outbreaks of S. agalactiae infection, characterized by septicemia, exophthalmia, and meningoencephalitis, has been reported among both farmed and wild fish species, which leads to high mortality of fishes and serious economic losses ( Olivares-Fuster et al, 2008 ; Mian et al, 2009 ; Soto et al, 2015 ).…”

Determinants of Group B streptococcal virulence potential amongst vaginal clinical isolates from pregnant women

“…GBS possesses an arsenal of virulence factors, which contribute to host cell attachment, invasion, colonization and progression of invasive disease [8]. The sialylated GBS capsular polysaccharide (CPS) represents one of the most critical virulence factors and, thus far, ten capsular serotypes have been identified (Ia, Ib and II–IX).…”