Notes on Streptococcus

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General Streptococcus Notes
• Gram-positive bacteria that produce lactic acid as end-product of their fermentative metabolism.
• They may grow in O2, but can only ferment.
• Cocci shaped and grow in chains of variable lengths.
• Inhabit the oral cavity and throat.
• S. pyogenes causes pharyngitis (sore throat) and other diseases.

Genus: Streptococcus.

• Gram +; cocci/pairs of cocci; catalase -;

Hemolysis:
• Beta = clear; alpha = partial (green); gamma = non-hemolytic.

Capsules: S. pneumoniae.
M-protein: S. pyogenes.

S. pyogenes:
• Beta-hemolytic; bacitracin sensitive.
• Beta-hemolytic; inhibited by bacitracin on blood agar.
• Found in human throat and skin; spread by respiratory droplets and direct contact.
• Causes infections such as strep throat, scarlet fever (due to pyrogenic exotoxin), and other conditions.
• Also causes wound infection and even death.
• Also causes necrotizing faciitis or "flesh eating disease."
• Beta-hemolytic, Gram-positive, chain-forming coccus with Lancefield group A cell wall polysaccharide.
• Causes sore throat.
• Produces enzymes that cause blood cell lyses.
• Colonies are surrounded by beta-hemolytic streptococci.
• Causes scarlet fever, acute glomerlonephiritis, acute rheumatic fever and cholera.

Pathogenesis:
• Hyaluronic acid capsule and M-protein inhibit phagocytosis.
• M12 strains cause acute glomerulonephritis.

Toxins:
• Streptolysins O and S.

Spreading factors:
• Streptokinase, streptococcal DNAse, hyaluronidase.

Exotoxins A-C:
• Fever and rash; inhibit clearnance of endotoxin.

Diseases:
• Acute (suppurative/pus-forming) Pharyngitis, scarlet fever, pyoderma/impetigo.
• Non-suppurative: rheumatic fever and acute glomerulonephritis.

Lab tests:
• Strep throat: rapid antigen test.
• Rheumatic fever: ASO titer.

Treatment:
• Beta-lactum drugs or erythromycin.

S. agalactiae:
• group B Streptococci.
• Beta-hemolytic; bacitracin resistant on blood agar; Group B.
• Catalase -;
• CAMP test +;

Found in vagina.

Pathegenesis:
• Capsule, beta-hemolysin, and CAMP factor.

Diseases: neonatal septicemia and meningitis.
Treatment: ampicillin with cefotaxime or gentamicin. Treat mom before delivery.

S. pneumoniae:
• Alpha-hemolytic, optochin sensitive in blood agar, Gram +, lysed by bile.
• Human upper respiratory tract.

Transmission:
• Respiratory droplets.

Causes pneumonia:
• Predisposed by: CHF, alcoholism, COPD, asplenia.

Pathogenesis:
• IgA protease: colonization.
• Teichoic acid: attachment.
• Polysaccharide capsule inhibits phagocytosis.
• Quellung reaction +.
• Pneumolysin damages respiratory epithelium.
• Meningitis confirmation: use latex agglutination test.

Diseases: bacterial pneumonia, meningitis, otitis media and sinusitis in children.
Treatment: penicillin G.

Viridians streptococci.
• Alpha-hemolytic; optochin resistant.
• Found in human oropharynx.

Diseases:
• Dental caries, infective endocarditis.

Pathgenesis:
• Dextran/biofilm mediated adherence.

Treatment:
• Penicillin G with aminoglycoside for endocarditis.

Other Types of Streptococcus
• Streptococcus agalactiae: found in the gut and female urogenital tract.
• Streptococcus mutans: found in the oral cavity; leads to tooth decay.
• Streptococcus pneumoniae: causes pneumonia.
• Streptococcus thermophilus: found in dairy products; used in yogurt production.

Additional Readings:

Basic Bacteriology

1. General Microbiology
2. Growth Medias and Oxygen Requirements
3. Staphylococus
4. Streptococcus
5. Enterococcus
6. Bacillus
7. Listeria
8. Corynebacterium
9. Actinomyces
10. Nocadria
11. Mycobacterium
12. Clostridium
13. Neisseria
14. Pseudomonas
15. Legionella
16. Bordetella
17. Francisella
18. Brucella
19. Campylobacter
20. Escherichia
21. Shigella
22. Klebsiella
23. Salmonella
24. Yersinia
25. Proteus
26. Vibrio
27. Pasteurella
28. Haemophilus
29. Bacteriodes and Prevotella
30. Treponema
31. Borrelia
32. Rickettsia
33. Coxiella
34. Ehrlichia
35. Chlamydia
36. Mycoplasma
37. What is an ELEK's Test?
38. Causes of Orchitis

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