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Pyogenic Coccus: Disease and Pathogenesis

Explore the major pathogenic species of pyogenic coccus, including Staphylococcus aureus, Streptococcus pyogenes, and Neisseria meningitidis. Learn about the diseases, pathogenesis, diagnosis, and treatment of these bacteria.

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Pyogenic Coccus: Disease and Pathogenesis

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  1. The labs in the next week are canceled, will be shifted to the following week. Labs will extend to 5.25 and 5.28.

  2. Coccus Zooming in pyogenic coccus: disease and pathogenesis

  3. Pyogenic coccus

  4. Pyogenic coccus

  5. Major pathogenic species • Staphylococcus (the staphylococcus) • Staphylococcus aureus • Staphylococcus epidermidis • Staphylococcus saprophyticus • Streptococcus (the streptococcus) • Streptococcus pyogenes • Streptococcus pneumoniae (the pneumococcus) • Neisseria (the neisseria) • Neisseria meningitidis (the meningococcus) • Neisseria gonorrhoeae (the gonococcus)

  6. Staphylococcus aureus • Diseases • Pathogenesis • Roles of bacterial virulent factors • Diagnosis • Methods for bacteria classification • Treatment and prevention • Issues

  7. Bacteria morphology • Staphylococcus : grape-like irregular clusters • Streptococcus : chains or pairs • Neisseria : kidney-shaped diplococci

  8. Bacteria culture: pigmentation • The bacteria produces liposoluble pigments which make the colonies appear in certain color: • Staphylococcus aureus golden yellow • Staphylococcus epidermidis white • Staphylococcus saprophyticus white or lemon yellow

  9. Bacteria culture: mannitol fermentation • Biochemical reactions: for example, Staphylococcus aureus is capable of using sugar mannitol (甘露醇) as a food source and will produce acidic byproducts of fermentation that will lower the pH of the media. • Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus pneumoniae and Streptococcus pyogenes on mannitol salt agar plates (containing 7.5% NaCl, mannitol and phenol red).

  10. Diseases I. Suppurative infections (化脓性感染) II. Toxicoses (毒素性疾病)

  11. I. Suppurative infections • Local infections (contained at the local) • Superficial skin lesions such as sore (疮), furuncle (疖) and stye (睑腺炎，麦粒肿) • Systemic infections (spread through the blood stream) • Septicemia (败血症) • Pyemia (脓血症): spread to different organs to cause pneumonia (肺炎), mastitis (乳腺炎), phlebitis (静脉炎), meningitis (脑膜炎), urethritis (尿道炎) and abscesses (脓肿)

  12. II. Toxicoses • Food poisoning • A gastrointestinal illness. Symptoms include nausea, vomiting, stomach cramps, and diarrhea. • Toxic shock syndrome (TSS,毒性休克综合征) • Characterized by a sudden onset of fever, chills, vomiting, diarrhea, muscle aches and rash. It can rapidly progress to severe and intractable hypotension and multisystem dysfunction. Commonly occurs in women. • Scalded skin syndrome (SSS, 烫伤样皮肤综合症) • Caused by staphylococcal skin infection. The skin blisters and peels off as though burned. Additional symptoms are fever, chills, and weakness. commonly occurs in infants.

  13. Pathogenesis • Cell wall virulent factors • Staphylococcal protein A (SPA) • Coagulase • Exotoxins • Staphylolysin (cytolytic) • Leukocidin (cytolytic) • enterotoxin (superantigen) • toxic shock syndrome toxin 1 (superantigen) • Exfoliatin (superantigen)

  14. Staphylococcal protein A (SPA) • Surface bound (in the cell wall) or free proteins. • Bind to Fc portion of IgG from human, mouse and guinea pig (but not to that from rabbit), and thus inhibit Fc receptor-mediated phagocytosis by macrophages.

  15. Inhibition of phagocytosis Fc receptor SPA IgG

  16. Agglutination test • In this test, anti-Staphylococcus aureus IgG can bind SPA using Fc fragment and the bacteria through Fab to from complexes that can been seen with eyes.

  17. Coagulase • Bound (in the cell wall): catalyzes fibrinogen (纤维蛋白原) into fibrin (纤维蛋白). Cause coating of the bacteria with fibrin and thus inhibit phagocytosis and killing mediated by serum components. • Free:secreted and turns into staphylothrombin after activation by cofactors in the plasma, which catalyzes fibrinogeninto fibrin. Cause coagulation of the plasma and helps to restrain infections at the local.

  18. Coagulase test and CNS • A test of coagulation of human or rabbit plasma in the presence of anticoagulant (citrate or heparin). • Coagulase-negative staphylococci (CNS) used to be thought as non-pathogenic, however, they have become a major source of hospital-acquired infections: • Staphylococcus epidermidis • Staphylococcus saprophyticus

  19. Cytolytic exotoxins: staphylolysin and leukocidin • Attack mammalian cell membranes, cause abscess and tissue necrosis. Often referred to as hemolysins. • Staphylolysins: • Four types: , ,  and  • Staphylolysin ,  and  can lyse erythrocytes (the basis for hemolytic reaction); toxic to many other cells such as white blood cells and muscle cells • Staphylolysin : close to leukocidin. • Leukocidin: lyse macrophages and neutrophils.

  20. Hemolysis test Bacteria are grown on sheep blood agar plates (containing 5% sheep blood): α- hemolytic reaction, partial hemolysis with a green coloration： Streptococcus pneumoniae β- hemolytic reaction, complete hemolysis： Staphylococcus aureus Streptococcus pyogenes γ - hemolytic reaction, no hemolysis: Staphylococcus epidermidis most strains Staphylococcus saprophyticus

  21. Superantigens • Superantigens can bind both to class II MHC molecules (but not in the peptide cleft) and also to a relatively conserved region of the TCR βchain. • This leads to non-specific activation of 2-20% of all T cells (vs. 0.01%), and massive unregulated cytokine release.

  22. Superantigen exotoxins: enterotoxin, TSST-1 , and exfoliatin • Enterotoxin, 9 serotypes, responsible for staphylococcal food poisoning. • TSST-1, close to enterotoxin, cause toxic shock syndrome (TSS). • Exfoliatin, 2 serotypes, cause staphylococcal scalded skin syndrome (SSS).

  23. Diagnosis • Pus • abscesses and superficial skin lesions • Sputum • lower respiratory tract infections • Blood • septicemia, pyemia • Food/feces or vomit • food poisoning • Mid-stream urine • urethritis

  24. Treatment and prevention • Antibiotics • MRSA refers to methicillin (甲氧苯青霉素)-resistant Staphylococcus aureus, and most MRSA strains are also multiple drug resistant • Chromosomal mutation • Plasmid-conferred • CNS, eg. Staphylococcus epidermidis • Biofilm formation • Exotoxin neutralizing antibodies • No vaccines available currently

  25. Summary Major pyogenic cocci Identification of Staphylococcus aureus and related bacteria (diagnosis) Diseases and molecular mechanisms Drug resistance and mechanisms

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