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Streptococcus
This document discusses the classification, structure, virulence factors, and important pathogens of the genus Streptococcus. It describes how streptococci are classified based on their hemolytic properties and Lancefield grouping. Key pathogens like S. pyogenes and S. pneumoniae are then discussed in more detail, outlining their morphology, culture characteristics, toxins/enzymes, mechanisms of pathogenesis, associated diseases, and treatment approaches.
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Streptococcus
- 1. Streptococcus Attribution-NonCommercial-ShareAlike 4.0 International (CCBY-NC-SA 4.0) For B.Sc Optometry Students
- 2. • gram-positive bacteria •spherical bacteria that characteristically form pairs or chains • Most are oxidase-negative and catalase-negative, and many are facultative anaerobes. • nonmotile, nonspore-forming • Most streptococci are facultative anaerobes, and some are obligate (strict) anaerobes Streptococcus – Structure
- 3. Streptococcus – Classifications Accordingto their O2 requirements they are either aerobic or anaerobic (peptostreptococci). A. Aerobic streptococci according to their action on RBC in blood agar (3 varieties): 1. Beta haemolytic streptococci: complete haemolysis (clear zone around the colonies on Blood Agar) e.g. S. pyogenes, S. agalactiae 2. Alpha haemolytic streptococci: partial haemolysis e.g. Viridans streptococci, S. pneumoniae 3. Non-haemolytic or gamma haemolytic streptococci: no haemolysis/ no change in RBC’s, e.g. Enterococci
- 4. Streptococcus – Classifications Bloodagar showing culture of streptococcus with different type of hemolysis. Note that in gama hemolysis there is no clear zone while in beta a prominent clear zone can be seen
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- 6. Lancefield Classification Streptococcus –Classifications • based on serologic reactivity of cell wall • polysaccharide Ags as originally described by R. Lancefield • >18 group-specific Ags (Lancefield groups A–H and K–U) were established according to the carbohydrate (C) Ag present in the cell wall. Group Example Diseases Group A S. Pyogenes S. pharyngitis strep throat, Scarlet fever, Impetigo, TSS, pneumonia, Rheumatic fever Group B S. agalactiae meningitis Group C S. equisimilis endocarditis, bactermia, meningitis Group D Enterococci UTI, endocarditis Group H S. sanguis endocarditis, dental caries Group K S. salivarius endocarditis, caries
- 7. Medically Important Streptococcus Attribution-NonCommercial-ShareAlike 4.0 International (CCBY-NC-SA 4.0) Streptococcus pyogenes
- 8. Streptococcus pyogenes Streptococcus –Medically Important Streps • Group A streptococcus (GAS) • GAS consists of 1 spp with 40 antigenic types • S. pyogenes, the most important human pathogen • causing diseases including: – Suppurative conditions / Skin infections – Throat infections – Systemic infections – Non-suppurative sequelae About 5-15% of normal individuals harbor the bacterium, in their respiratory tract, without signs of disease.
- 9. Streptococcus pyogenes Streptococcus –Medically Important Streps Morphology: • Gram-positive cocci arranged in chains of varying length & are non motile. • Some strains are capsulated. Cultural characters: • Forms minute colonies • It grows on blood agar producing β-haemolysis Antigens • The cytoplasmic membrane of S. pyogenes has Ags similar to those of human cardiac, skeletal, smooth muscle, heart valve fibroblasts and neuronal tissues, resulting in a molecular mimicry.
- 10. Virulence factors ofgroup A streptococci: 1. M – protein, fibronectin-binding proteins (e.g. F protein) & lipoteichoic acid for attachment 2. Hyaluronic acid capsule: inhibits phagocytosis 3. Exotoxins such as pyrogenic toxin, cause the rash of scarlet fever & systemic toxic shock syndrome 4. Invasins - Streptokinase, streptodornase (DNaseB), hyaluronidase & streptolysins Streptococcus – Medically Important Streps - Streptococcus pyogenes
- 11. Streptococcus – MedicallyImportant Streps - Streptococcus pyogenes Protein antigens: S. pyogenes: divided into types based on their content of M protein (about 80 types described). • M protein: - the most important virulence factor - is antiphagocytic - promotes adherence to host epithelial cells • The protein and other cell wall Ags have important role in the pathogenesis of rheumatic fever. • Antibodies to these components react with cardiac muscle tissue. • Other antigens are the T & R proteins - but they are not related to virulence.
- 12. Streptococcus – MedicallyImportant Streps - Streptococcus pyogenes Toxins and Enzymes: • More than 20 extracellular products that are antigenic are produced by S. Pyogenes. Some of the important toxins and enzymes include: 1. Streptokinase (fibrinolysin): transforms the plasminogen of human plasma into plasmin, an active proteolytic enzyme that digests fibrin and other proteins, which can dissolve fibrin in clots, thrombi and emboli, causes fibrinolysis. 2. Streptodornase (deoxyribonuclease): depolymerizes DNA, are DNAses (types A, B, C, D) that break down DNA. Streptokinase and streptodornase are responsible for the spreading nature of streptococcal infections.
- 13. Streptococcus – MedicallyImportant Streps - Streptococcus pyogenes 4. Hyaluronidase: – It destroys hyaluronic acid, the cement substance of connective tissue. - It helps spreading of infection. 5. Streptococcal pyrogenic exotoxins (SPE) (formerly erythrogenic toxin): – An exotoxin produced by some strains of group A streptococci – Act as superantigens – It causes vasodilatation of capillaries leading to the rash of scarlet fever. 6.
- 14. Streptococcus – MedicallyImportant Streps - Streptococcus pyogenes 6. Streptolysins: There are 2 types: a. Streptolysin O - (O2 labile): – Antigenic, stimulates the production of anti-streptolysin O (ASO) Abs that can be measured in patients serum. b. Streptolysin S - (O2 stable): – Not antigenic, does not stimulate production of Ab – It hemolyzes red cells and is responsible for the beta – haemolysis produced on blood agar
- 15. Streptococcus – MedicallyImportant Streps - Streptococcus pyogenes Virulence factors Protein antigens M protein T and R protein Enzymes Streptokinase (fibrinolysin) Streptodornase Hyaluronidase Streptolysin Toxins Streptococcal pyrogenic exotoxins
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- 18. Streptococcus – MedicallyImportant Streps - Streptococcus pyogenes Erysipelas • If the portal of entry is the skin, erysipelas results • massive brawny edema and a rapidly advancing infection. Diseases caused by Invasion by S. pyogenes
- 19. Streptococcus – MedicallyImportant Streps - Streptococcus pyogenes Cellulitis • An acute, rapidly spreading infection of the skin and subcutaneous tissues. • It follows infection associated with mild trauma, burns, wounds, or surgical incisions. • Pain, tenderness, swelling, and erythema occur. Cellulitis Vs erysipelas: In cellulitis, the lesion is not raised, and the line between the involved and uninvolved tissue is indistinct.
- 20. Streptococcus – MedicallyImportant Streps - Streptococcus pyogenes Necrotizing Fasciitis (Streptococcal Gangrene) • infection of the subcutaneous tissues and fascia. • extensive and very rapidly spreading necrosis of the skin and subcutaneous tissues. • The group A streptococci that cause necrotizing fasciitis have sometimes been termed "flesh-eating bacteria.“ • A major risk factor for the development of streptococcal necrotizing fasciitis is a history of recent varicella-zoster virus (VZV) infection Bacteremia/Sepsis Infection of traumatic or surgical wounds with streptococci results in bacteremia, which rapidly can be fatal. S pyogenes bacteremia can also follow skin infections, such as cellulitis and pharyngitis.
- 21. Streptococcus – MedicallyImportant Streps - Streptococcus pyogenes Diseases Caused by Local Infection with S pyogenes Streptococcal Sore Throat/ pharyngitis • most common infection • S. pyogenes adhere to the pharyngeal epithelium by means of lipoteichoic acid • glycoprotein fibronectin on epithelial cells probably serves as lipoteichoic acid ligand. • cervical lymph nodes are usually enlarged. • intense nasopharyngitis, tonsillitis, and intense redness and edema of the mucous membranes, with purulent exudate, and a high fever A similar clinical picture can occur with infectious mononucleosis, diphtheria, gonococcal infection, and adenovirus infection.
- 22. Streptococcus – MedicallyImportant Streps - Streptococcus pyogenes Streptococcal Pyoderma/ impetigo • Local infection of superficial layers of skin • It consists of superficial vesicles that break down • eroded areas is covered with pus and later is encrusted • highly communicable, especially in hot, humid climates. • may progress to cellulitis. A clinically identical infection can be caused by S aureus and sometimes both S pyogenes and S aureus are present. Diseases Caused by Local Infection with S pyogenes
- 23. Streptococcus – MedicallyImportant Streps - Streptococcus pyogenes • Following an acute S pyogenes infection, there is a latent period of 1–4 weeks, after which nephritis or rheumatic fever occasionally develops. • Due to a hypersensitivity response • Nephritis is more commonly preceded by infection of the skin • Rheumatic fever is more commonly preceded by infection of the respiratory tract Acute Glomerulonephritis • develops 3 weeks after S pyogenes skin infection (pyoderma, impetigo) • Specifically in case of M type infections. • initiated by antigen-antibody complexes on the glomerular basement membrane. • blood and protein in the urine, edema, high blood pressure, and urea nitrogen retention • may develop chronic glomerulonephritis with ultimate kidney failure - the majority recover completely. Poststreptococcal Diseases
- 24. Streptococcus – MedicallyImportant Streps - Streptococcus pyogenes Rheumatic Fever • results in damage to heart muscle and valves. • strains of group A streptococci contain cell membrane antigens that cross-react with human heart tissue antigens. • preceded by S pyogenes infection 1–4 weeks earlier – may not be detected • Typical symptoms and signs: fever, malaise, a migratory non suppurative polyarthritis, and evidence of inflammation of all parts of the heart (endocardium, myocardium, pericardium). • carditis characteristically leads to thickened and deformed valves that are finally replaced by scar tissue. • can be reactivated by recurrent streptococcal infections, whereas nephritis does not. • first infection produces only slight cardiac damage - increases with each subsequent infection. • prophylactic penicillin administration.
- 25. Medically Important Streptococcus Attribution-NonCommercial-ShareAlike 4.0 International (CCBY-NC-SA 4.0) Streptococcus pneumoniae
- 26. Streptococcus – MedicallyImportant Streps - Streptococcus pneumoniae • gram-positive • lancet-shaped diplococci are often seen in specimens of young cultures. • In sputum or pus, single cocci or chains are also seen. • With age, the organisms rapidly become gram-negative and tend to lyse spontaneously • the growth of pneumococci is inhibited around a disk of Optochin
- 27. Streptococcus – MedicallyImportant Streps - Streptococcus pneumoniae • the growth of pneumococci is inhibited around a disk of Optochin • Note that viridans streptococci are not inhibited by Optochin.
- 28. Streptococcus – MedicallyImportant Streps - Streptococcus pneumoniae Pneumococci are α-hemolytic on blood agar
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- 30. Streptococcus – MedicallyImportant Streps - Streptococcus pneumoniae Production of Disease • produce disease through their ability to multiply in the tissues. • They produce no toxins of significance. • The virulence of the organism is a function of its capsule, which prevents or delays ingestion by phagocytes.
- 31. Streptococcus – MedicallyImportant Streps - Streptococcus pneumoniae Loss of Natural Resistance • the normal respiratory mucosa must possess natural resistance to the pneumococcus. 1. Viral and other respiratory tract infections that damage surface cells; abnormal accumulations of mucus (eg, allergy), which protect pneumococci from phagocytosis; bronchial obstruction; and respiratory tract injury due to irritants disturbing its mucociliary function. 2. Alcohol or drug intoxication, which depresses phagocytic activity, depresses the cough reflex, and facilitates aspiration of foreign material. 3. Abnormal circulatory dynamics (eg, heart failure). 4. Other mechanisms, eg, malnutrition, general weakness, sickle cell anemia, hyposplenism, nephrosis, or complement deficiency
- 32. Streptococcus – MedicallyImportant Streps - Streptococcus pneumoniae Clinical Findings • sudden, with fever, chills, and sharp pleural pain. • sputum is similar to the alveolar exudate, being characteristically bloody or rusty colored. • From the respiratory tract pneumococci may reach other sites. • sinuses and middle ear are most frequently involved. • Infection sometimes extents to the meninges. • Bacteremia from pneumonia has a triad of severe complications: meningitis, endocarditis, and septic arthritis. • With antimicrobial therapy, the illness is usually terminated promptly
- 33. Streptococcus – MedicallyImportant Streps - Streptococcus pneumoniae Treatment • Penicillin G is the drug of choice • Some penicillin-resistant strains are resistant to cefotaxime. • Resistance to tetracycline and erythromycin occurs also. • Pneumococci remain susceptible to vancomycin.
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- 35. Streptococcus – Ocularinfections caused by Streptococcus Major Ocular infections caused by Streptococcus are • Acute bacterial conjunctivitis • Bacterial Keratitis/Corneal Ulcers • Periorbital Cellulitis • Endophthalmitis
- 36. Streptococcus – Treatmentand chemoprophylaxis Treatment and Chemoprophylaxis: • Penicillin is the drug of choice for treatment of streptococcal diseases. • penicillins G injections : given as prophylactic measure to children prone to recurrent attacks of streptococcal sore throat or recurrent attacks of RF. • Erythromycin is also effective, BUT Erythromycin resistance • Macrolide resistance in ß-haemolytic streptococci of Lancefield groups A, B, C, G