1. Streptococci & Pneumococci

2. Streptococci: Gram-positive cocci

3. Streptococci Form chains Catalase negative Grow aerobically
Gram-positive cocci
Form chains
Catalase negative
Grow aerobically
and anaerobically

4. “Strep” throat

5. Scarlet Fever

6. Necrotizing fasciitis

7. Hemolysis on blood agar - a tool to classify Streptococci
b-hemolysis: clear zone
a-hemolysis: green zone
g -hemolysis: none

8. Lancefield Group used to classify Streptococci A to T
“A Serological Differentiation of Human
and other Groups of Hemolytic Streptococci”
Journal of Experimental Medicine, 1933
carbohydrate antigens in cell wall
used to classify Streptococci
A to T
A and B: most significant as pathogens
Example: “Group A Strep” = GAS

9. Medically Important Streptococci
Lancefield Diagnostic Species Group Hemolysis Feature Primary Diseases
S. pyogenes A b BacitracinS “Group A Strep”
S. agalactiae B b BacitracinR neonatal meningitis
Enterococcus D a, g Grows in endocarditis, UTI,
faecalis high NaCl biliary tract infections
Classification Schemes:
Species
Lancefield Grouping:
Rebecca Lancefield
Based on cell well associated carbohydrate
A to T
Hemolytic Activity on blood agar
a-colonies have green halo; partial lysis
b-clear halo; complete lysis
g-no halo
Viridans none a Bile insoluble dental caries,
endocarditis
S. pneumonia none a Bile soluble “pneumococcus”,
pneumonia

10. Caused by Group A Streptococcus:
Three Types of Disease
Caused by Group A Streptococcus:
1. Pyogenic or Suppurative
-pharyngitis
-impetigo
2. Pyrogenic
-scarlet fever
-toxic shock syndrome
-puerperal fever
3. Immunologic
-rheumatic fever
-acute glomerulonephritis

11. Natural Reservoir of Streptococci:
Normal Human Flora
S. pyogenes -skin, mucous membranes
S. agalactiae -lower GI, female genital tract
E. faecalis -GI and genitourinary tract
Viridans -oropharynx

12. Traits of a Successful Pathogen
Entry
Adherence
Multiplication
Spread
Immune evasion
Transmission to other hosts
Entry -- how the agent enters the host
Adherence --how the agent attaches to a certain substrate in the host (not required for all pathogens)
Multiplcation --How does the agent obtain what it needs to grow
Spread -- not necessary for all pathogens; depends upon the major site of replication (i.e., does the organism need to spread to complete its life cycle?); Often, spread can be regarded as an unnecessary and untoward complication of infection that has no benficial consequences for the infecting organism .
Immun evasion-How does the organism prevent being eliminated by the host?
Persistence -- some infections become chronic or latent.
Dissemination - How does the organim exit the host in order to be transmitted to the next host.

13. Hanski and Caparon, 1992 PNAS 89: 6172-6176.
S. pyogenes adherence to respiratory epithelium requires F, a fibronectin-binding protein.
F and M
M only
F only
neither
Hanski and Caparon, 1992 PNAS 89:

14. Evolution of Host-Pathogen Interactions
Humans evolved under continuous exposure
to a rich variety of microbes.
Consequently, the human immune system
is quite sophisticated and efficient.
BUT-
the immune system exerts a
strong selective pressure on microbes,
which have the advantage of
a much shorter generation time:
~ 1 h versus ~ 25 years.

15. Immune Evasion by Group A Strep
C5a peptidase
- destroys C5a chemotactic activity
M protein
- disrupts alternate pathway
of complement deposition
Hyaluronic acid capsule
- antiphagocytic
- host mimicry
- invasion

16. M protein of Group A Strep
Major surface protein
In a mouse model, required for full virulence
Resistance to phagocytosis
Blocks complement opsonization
~ 100 serotypes
In a mouse model, immunization generates
type-specific immunity.
Some epitopes cross-react with heart tissue:
potential trigger of autoimmune disease

17. Y M Protein of Group A Strep blocks complement-mediated phagocytosis H
N-terminus H Y
Protective, opsinizing antibodies
recognize diverse epitopes.
hypervariable
Fibrinogin- and fibrin-binding
blocks complement deposition.
variable
Factor H inhibits C3 maturation.
conserved
C-terminus

18. Capsule prevents Group A Streptococcus
from entering epithelial cells
surface
intracellular

19. Group A Strep Virulence Factors:
Invasion and Damage
1. Digestive enzymes promote spread
Hyaluronidase
-degrades extracellular matrix
Streptokinase
-”clot buster” marketed for clinical use
- converts plasminogen to plasmin,
which degrades extracellular matrix proteins,
including fibrin.
Streptolysins O and S
-a and b hemolysis
DNase B

20. Group A Strep Virulence Factors:
Invasion and Damage
2. Streptococcal Pyrogenic Exotoxins
- red rash of scarlet fever
- SPE A, B, and C
- encoded by bacteriophages
carried by some, not all, strains
- similar to toxin of Staph. aureus
that causes toxic shock syndrome
- superantigens: septic shock

21. Superantigen Mode of Action
normal antigen
superantigen
Superantigen
Mode of Action
SpeA, B, and C toxins
are superantigens.
Salyers and Whitt,
Bacterial Pathogenesis,
A Molecular Approach

22. Two non-suppurative sequellae
of Group A Strep
1. Acute Glomerulonephritis
Can follow either pharyngitis or impetigo
Attack rate can be high: ~ 40%
2. Rheumatic Fever
Only caused by Group A Strep
Only follows infections of pharynx
Only some patients are susceptible

23. Hypothesis: Pathogenesis of Rheumatic Fever
Pathogenesis of Acute Glomerulonephritis

24. oval or “lancet”-shaped encapsulated diplococci
Streptococcus pneumonia: Gram-positive diplococci
Gram stained
sputum sample
oval or “lancet”-shaped
encapsulated diplococci

25. Pneumococcal Disease 7 million cases of otitis media In the U.S.
3,000 cases of meningitis
50,000 cases of bacteremia
500,000 cases of pneumonia
7 million cases of otitis media
In developing countries
5 million children under the age of 5 die each year from pneumonia

26. Asymptomatic Carriage vs Disease
Natural reservoir: naso- and oropharynx
of healthy people
Transmission: respiratory droplets
Host defenses: mucocilliary action,
cough reflex, alveolar macrophages
Predisposing factors:
young age, old age
viral respiratory infection
chronic disease
Alcoholism
Diabetes
Splenic dysfunction
HIV

27. Colonization
Microbiology, Prescott, Harley, and Klein

29. Predisposition

30. Pneumonia

31. Immune evasion: IgA1 proteases
deleted hinge
region
hinge region L H L H
IgA1
IgA2
Pro-Ser-Thr-Pro-Pro-Thr-Pro-Ser-Pro-Ser-Thr-Pro-Pro-Thr-Pro-Ser-Pro-Ser-Cys
H. influenzae
(~95%)
S. pneumoniae (100%)
S. sanguis (~70%)
N. meningitidis
(99%)
N. gonorrhoeae
(100%)

32. Pneumolysin related to streptolysin O of Group A Strep
binds cholesterol and multimerizes to form transmembrane pores
two activities
activates complement
cytotoxicity
released by autolysis, not secretion
antigenically conserved

33. LUNG BLOOD After endotracheal infection of mice,
pneumolysin promotes lung colonization and sepsis.
LUNG
BLOOD WT WT
mutant
mutant
Rubins et al., 1995
J. Clin. Invest. 95:

34. Pneumolysin: a role in virulence
mutants have greatly increased LD50
pneumolysin alone produces the pathology seen in pneumonia
analysis of site-specific mutants indicate pathology is attributable to both cytotoxicity and complement activation
acts as a protective antigen in both native and toxoid forms
protection independent of capsular serotype

35. Pneumococcal Polysaccharide Capsule
all isolates encapsulated
spontaneous and genetically engineered Cap- mutants are avirulent
enzymatic depolymerization of capsule increases LD fold
antiphagocytic properties
precise mechanism unclear
blocks direct contact with phagocyte receptors
over 80 distinct serotypes

36. Paradigm Capsular polysaccharides serve as both virulence factors
and protective antigens
in bacteria
whose primary pathogenic event
is invasion of the bloodstream.
Examples:
Primary = tuberculosis
Secondary = Pseudomonas aeruginosa, Staph. aureus
Opportunistic = Pneumocystis carinii.
Are these distinctions valid?
The nature of the host and the situation plays a role in the establishment of most infections.

38. Pneumococcus triggers inflammation:
interaction with complement pathway
Activates
complement
cascade
Blocks
complement-mediated
phagocytosis

39. Robust host inflammatory response is primary cause of pneumococcal disease symptoms.
- PMN chemoattractant
- inflammation
- tissue damage
C3b
- opsonin, promotes phagocytosis by PMNs
- ineffective due to capsule
C3a, C4a, C5a
- trigger mast cell release of histamine
- increase vascular permeability, fluid accumulation