Group B streptococcal infection pathophysiology

The gastrointestinal tract serves as the primary reservoir for Group B Streptococcus (GBS) and is the likely source of vaginal colonization. Early-onset neonatal infections are acquired vertically through exposure to GBS from the vagina of a colonized woman. GBS is characterized by its ability to adhere to epithelial surfaces, such as the vagina, placental membranes, blood brain barrier, and respiratory tract. GBS can penetrate the host cell barriers and evade the host’s immune response. The polysaccharide antiphagocytic capsule is this bacterium’s main virulence factor.

GBS is characterized by its ability to adhere to epithelial surfaces, particularly the vaginal mucosa where the pH is low. The types of epithelium to which GBS adheres to are:

• Vagina
• Placental membranes
• Blood brain barrier
• Respiratory tract

The series of events that explain the pathogenesis of GBS infection can be summarized as follows:^[1]

• Extracellular matrix binding
• Direct cellular injury
• Invasion of epithelial cells and brain endothelium
• Resistance to intracellular killing
• Resistance to phagocytosis
• Activation of inflammatory cells
• Recruitment of neutrophils in the central nervous system

The polysaccharide antiphagocytic capsule is this bacterium’s main virulence factor.

Other key virulence factors include:^[1]

• Beta-hemolysin
• C protein
• C5a peptidase
• CAMP factor
• Fibrinogen receptor
• Hyaluronate lyase
• Lipotechoic acid
• Serine protease

The gastrointestinal tract serves as the primary reservoir for GBS and is the likely source of vaginal colonization.^[2]

Early-onset infections are acquired vertically through exposure to GBS from the vagina of a colonized woman. Neonatal infection occurs primarily when GBS ascends from the vagina to the amniotic fluid after onset of labor or rupture of membranes, although GBS also can invade through intact membranes. GBS can be aspirated into the fetal lungs, which in turn can lead to bacteremia. Infants also can become infected with GBS during passage through the birth canal; infants who are exposed to the organism through this route can become colonized at mucus membrane sites in the gastrointestinal or respiratory tracts, but these colonized infants most commonly remain healthy.^[2]

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