Streptococcus agalactiae

Group B Strep (GBS): Neonatal Disease
Classic Case: Group B Strep

A 3 day old newborn presents with a fever, difficulty breathing, cough, nuchal rigidity, and appears quite ill. Analysis of CSF reveals gram-positive cocci that are catalase negative, and resistant to bacitracin.

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Causative Agent of:
  • Neonatal Sepsis, Pneumonia, Meningitis
    • Newborn infants
    • Most common cause of neonatal sepsis (U.S.)
  • aka “Group B Strep” (GBS)
Physical Features
  • Gram-positive
  • Coccus
  • Non-Motile
  • Encapsulated: Polysaccharide (11 serotypes)
  • Group B Lancefield type
    • (Group B Strep: GBS)
Growth Features
  • β-hemolytic
    • Clear area on blood agar
    • Complete hemolysis
  • Catalase negative
  • Bacitracin resistant
  • Hydrolyses hippurate
Epidemiology
  • Normal flora of GI, genitourinary tracts
  • Transient normal flora of >20% of pregnant women
    • (If untreated, high transmission risk to newborn)
  • U.S.: > 25,000 severe GBS infections/yr
    • Neonatal risk: <0.3/1000 live births
    • Most common cause of neonatal sepsis
    • 80% drop since ’93
    • (Moms are screened)
Reservoir and Transmission

Reservoir:

  • Humans
  • Colonizes GI and genitourinary tracts
    • >20% of pregnant women are colonized

Transmission:

  • Early-onset disease:
    • To neonates via birth canal
    • (or post-membrane rupture but before delivery)
  • Late-onset neonatal disease:
    • Via person-to-infant contact
Risk Groups
  • Neonates: Risk during delivery
  • Newborns: Risk post-partum
S agalactiae SEM Computer image

S. agalactiae, digitized SEM

General Streptococcus gram stain

Gram stain, Streptococcus sp.

Hemolysis diagram

Types of Hemolysis

Clinical

Group B Strep
Symptoms
  • Neonates:
    • Most Common Neonatal Cause of meningitis, pneumonia and sepsis
  • Early-onset: <7 days old
    • Symptoms usually seen within few hrs of birth
    • Sepsis most common outcome
    • Pneumonia (10%), meningitis (5%)
    • Abnormal temperature/heart rate/breathing
    • Mortality rate of ~5%
    • Neurological sequelae frequent with survival
  • Late-onset: 1 week to 3 months old
    • Bacteremia, meningitis
    • Lower mortality and sequelae
  • Adult diseases: Less common than neonatal
    • Pregnant women: UTIs, endometritis
  • Immunocompromised adults:
    • Bacteremia, endocarditis, pneumonia
    • Skin/joint/soft tissue infections
Pathogenesis
  • Polysaccharide capsule helps to avoid phagocytosis
  • Neonates are unable to phagocytose bacteria
  • Inflammation causes most disease symptoms
    • Similar to other Streptococci
  • 15-30% of isolates:
    • Resistant to erythromycin or clindamycin
Diagnosis
  • Culture and staining from bodily fluids (blood, CSF)
  • PCR testing: Rapid (1 hour) and sensitive
    • Has not yet replaced culture methods
Prevention
  • Screening of expectant mothers in third trimester
  • Antibiotic prophylaxis for mothers:
    • = Large decrease in early-onset disease
    • But no effect on late-onset disease
    • (Late-onset often via other caregivers)
Treatment
  • Penicillin G
  • Serious illness (or allergy to penicillin)?
    • Aminoglycosides or vancomycin
References
  1. The CDC on Streptococcus agalactiae
  2. Neonatal group B streptococcal disease. 2011. Clin. Micro. Infect. 17:1294.
  3. A Maternal Vaccine against Group B Streptococcus: Past, Present, and Future. 2013. Vaccine. 31:D13.
  4. Neonatal infections: group B streptococcus. 2014. BMJ Clin. Evid. 2014: 0323.
  5. Epidemiology of Group B Streptococcal Disease in the United States. 1998. Clin. Microbiol. Rev. 11:497.
  6. Prevention of Perinatal Group B Streptococcal Disease: Revised Guidelines from CDC, 2010. MMWR. 59:1.

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