1. Streptococcus agalactiae (GBS)

2. Streptococci Characters of Streptococci Gram positive cocci
1µm in diameter
Chains or pairs
Usually capsulated
Non motile
Non spore forming
Fastidious
Catalase negative (Staphylococci are catalase positive)

3. Streptococcus agalactiae (GBS)
Physiology and Structure
Gram (+) streptococci
Facultative anaerobe
β –hemolytic (1-2% are nonhemolytic)
Classified by B antigen

5. Streptococcus agalactiae

6. Streptococcus agalactiae
Epidemiology
Site of colonization:
Lower gastrointestinal tract
Genitourinary tract
10% to 30% of pregnant women are carriers.
60% of infants born to colonized mothers become infected with mothers’ organisms.
This can lead to pneumonia, bacteremia, and meningitis

7. Streptococcus agalactiae
Epidemiology cont.
Infections in men and non-pregnant women:
Primarily skin and soft-tissue
Bacteremia
Urosepsis (UTI with bacteremia)
Pneumonia
Conditions that predispose disease in adults:
Diabetes mellitus
Cancer
Alcoholism

8. Pathogenesis
Fig. 1. Stages in the molecular and cellular pathogenesis of neonatal group B Streptococcal (GBS) infection.
Doran, Kelly S. & Nizet, Victor. Molecular pathogenesis of neonatal group B streptococcal infection: no longer in its infancy. Molecular Microbiology  2004;54:23-31.

9. Virulence Factor GBS Surface Polysaccharide Capsule
Antiphagocytic properties
Capsule-deficient mutants diminished virulence in animal models
Sialic acid residues on capsule inhibit the binding of opsonically-active C3 component of complement to the cell surface
blocking activation of the alternative pathway
Transplacental passage of type-specific anticapsular IgG antibody from mother to infant is an important protective factor against invasive disease

10. Virulence Factor GBS β-hemolysin
Cytotoxic to pulmonary epithelial and endothelial cells
Pulmonary injury and alveolar protein exudate in early-onset pneumonia
Activity is blocked by surfactant phospholipid
Increased risk of premature, surfactant-deficient neonates for severe pneumonia
Induces cytokine release and nitric oxide production in macrophages
Stimulate elements of the sepsis cascade

11. Virulence Factor C5a-peptidase
Cleaves and inactivates the complement-derived neutrophil chemoattractant C5a
C5a-peptidase-deficient mutants are more rapidly cleared from the lungs of infected animals when compared to the isogenic wild-type strain

12. Hemolysis on Blood agar

13. Bacitracin sensitivity
Principle:
Bacitracin test is used for presumptive identification of group A
To distinguish between S. pyogenes (susceptible to B) & non group A such as S. agalactiae (Resistant to B)
Bacitracin will inhibit the growth of gp A Strep. pyogenes giving zone of inhibition around the disk
Procedure:
Inoculate BAP with heavy suspension of tested organism
Bacitracin disk (0.04 U) is applied to inoculated BAP
After incubation, any zone of inhibition around the disk is considered as susceptible

14. CAMP test Principle: Procedure:
Group B streptococci produce extracellular protein (CAMP factor)
CAMP act synergistically with staph. -lysin to cause lysis of RBCs
Procedure:
Single streak of Streptococcus to be tested and a Staph. aureus are made perpendicular to each other
3-5 mm distance was left between two streaks
After incubation, a positive result appear as an arrowhead shaped zone of complete hemolysis
S. agalactiae is CAMP test positive while non gp B streptococci are negative

15. CAMP test

17. Enhanced Zone of Hemolysis
CAMP Factor Test
S. aureus
(Sphingomyelinase C)
Group B Streptococcus
(CAMP Factor)
Group A Streptococcus
Enhanced Zone of Hemolysis

18. Optochin Susceptibility Test
Optochin resistant
S. viridans
Optochin susceptible
S. pneumoniae

19. Differentiation between -hemolytic streptococci
CAMP test
Bacitracin
sensitivity
Hemolysis
Negative
Susceptible 
S. pyogenes
Positive
Resistant
S. agalactiae

20. Hippurase NEG

21. Grp B Streptococci
and
Campylobacter
Hippurase POS

22. Streptococcus agalactiae
Diagnosis
Culturing
Antigen Detection
DNA (PCR) test
Treatment
Penicillin G
Pregnant women are give IV 4 hours before delivery

23. Diagnosis and Screening
Culture– Gold Standard
Selective broth medium (SMB or Lim Broth)
PCR (Berger, et al 2000)
Comparable in sensitivity to culture in extremely controlled laboratory environment
Limited studied of clinical practice
Immunoassay
Enzyme and Optical
Poor sensitivity
Antigen detection may assist with diagnosis of CSF infection
Bergeron MG, et al. Rapid detection of GBS in pregnant women at delivery. NEJM 2000;343:175.

24. Key Identification Characteristics of streptococcus agalactiae
Test
Reaction
Hemolysis
Catalase
Bacitracin 0.04U
SXT
CAMP test
Bile esculin
Optochin
Hydrolysis of hippurate
PYR
Beta - R +