Hazim abdul Wahhab General characters of streptococci Spherical cocci arranged in chain or pairs Gram positive Most streptococci are facultative anaerobes All Streptococci are catalase negative ID: 1043008
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2. StreptococcusDr. Batool Hazim abdul Wahhab
3. General characters of streptococci: Spherical (cocci) arranged in chain or pairs. Gram- positive. Most streptococci are facultative anaerobes. All Streptococci are catalase negative. Fastidious organism. Non-motile.
4. General Characteristics of streptococci: Non-spore forming. Group A streptococci have a hyaluronic acid capsule. Most require enriched media (blood agar). Older cultures may lose their Gram-positive character.
5. Streptococcus
6. Properties (Important):One of the most important characteristics for identification of Streptococci is the type of hemolysis.Types of Streptococci hemolysis include: Alpha- hemolytic Streptococci: form green zone around their colonies as a result of incomplete lysis of red blood in the agar as (S. pneumoniae and Viridans group Streptococci).Beta- hemolytic Streptococci: form a clear zone around their colonies because complete lysis of the red blood cells Gamma- hemolytic Streptococci (Nonhemolytic).
7. S. Pyogenes (beta- hemolytic)Hemolysis on the blood agar.
8. SpeciesLancefield GroupTypical HemolysisDiseasesDiagnostic FeaturesS. pyogenesABeta1- Bacterial cause as (Pharyngitis, cellulitis). 2- Immunologic diseases (Rheumatic fever, Acute glomerulonephritis) Bacitracin-sensitiveS. agalactiaeBBetaNeonatal sepsis, MeningitisBacitracin-resistantS. faecalisDAlpha or Beta or NoneHospital-acquired urinary tract infections, EndocarditisGrowth in 6.5 % NaCl S. bovisDAlpha or NoneEndocarditisNo Growth in 6.5 % NaClS. pneumoniaeNAAlphaPneumonia, Bacteremia, Meningitis and Infections of the upper respiratory tract as (Otitis media and sinusitis)Bile- Soluble; inhibited by optochinViridans groupNAAlphaEndocarditisNot Bile- Soluble; not inhibited by optochinTable 1: Streptococci of medical importance
9. What is the meaning of Lancefield?Lancefield grouping is a system of classification that classifies catalase-negative Gram-positive cocci based on the carbohydrate composition of bacterial antigens found on their cell walls.
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11. Beta- hemolytic Streptococci with Two important Antigens:1- C- carbohydrate: is located in the cell wall, and its specificity is determined by an amino sugar (determines the group of beta- hemolytic Streptococci.2- M- protein: - Is the most important virulence factor and determines the group A beta- hemolytic Streptococci.- It protrudes from the outer surface of the cell and interferes with ingestion by phagocytes.-There are approximately (80) serotypes based on the M- protein (This explains why multiple infections with S. pyogenes can occur) for example :- Strains of the S. pyogenes that produce certain M- protein types are (Rheumatogenic) cause Rheumatic fever.- While strains of the S. pyogenes that produce other M- protein types are (Nephritogenic) cause acute glomerulonephritis.Note: S. pyogenes contain M- protein as the main antiphagocytic component, also contain polysaccharide capsule that plays a role in the retarding phagocytosis.
12. Pathogenesis, enzymes, toxins and Clinical Findings for the: 1- S. pyogenes (group A Streptococci). 2- Group B Streptococci.
13. Pathogenesis:S. pyogenes (group A Streptococci) cause disease by three mechanisms:1- Pyogenic Inflammation: which is induced locally at the site of the organism in tissue.2- Exotoxin Production: which cause wide spread systemic symptoms in areas of the body where there are no organisms. 3- Immunologic: which occurs when antibody against a component of the organism cross-reacts with normal tissue or forms immune complexes that damage normal tissue. Immunologic reactions cause inflammation as in the inflamed joints of rheumatic fever, but there are no organisms in the lesions.
14. OrganismType of PathogenesisTypical DiseaseMain site of disease (D), Colonization (C), or Normal Flora (NF)S. pyogenes (group A)1- Pyogenica- Local. b- Disseminated. 2- Toxigenic. 3- Immune-mediated (post-streptococcal, nonsuppurative).………Impetigo, Cellulitis,Pharyngitis. Sepsis. Scarlet fever, Toxic shock. Rheumatic fever,Acute glomerulonephritis. Skin (D)Throat (D) Blood stream (D) Skin (D)Many Organs (D) Heart, Joints (D)Kidney (D)S. agalactiae (group B)PyogenicNeonatal sepsis and MeningitisVagina (C)S. faecalis (group D)PyogenicUrinary tract infection, EndocarditisColon (NF)S. bovis (group D)PyogenicEndocarditisColon (NF)S. pneumoniaePyogenicPneumonia, Otitis media,MeningitisOropharynx (C)Viridans groupPyogenicEndocarditisOropharynx (NF)Table 2: Important features of pathogenesis by Streptococci.
15. S. pyogenes (group A) and streptococcal diseases.
16. Enzymes of the Streptococci:Group A Streptococci: produce three important inflammation-related enzymes:1- Hyaluronidase: degrades hyaluronic acid, which is the ground substance of subcutaneous tissue.Hyaluronidase is known as a spreading factor because is facilitates the rapid spread of S. pyogenes in the skin infections as in (cellulitis). 2- Streptokinase: (fibrinolysin) activates plasminogen to form plasmin, which dissolves fibrin in clots, thrombi, and emboli. It can be used to lyse thrombi in the coronary arteries of heart attack patients. 3- DNase (streptodornase): depolymerizes DNA in exudates or necrotic tissue.Important Note: Streptokinase- Streptodornase mixtures applied in diagnostic purpose give a positive reaction in most of adults indicating cell- mediated immunity.Group B Streptococci: No cytotoxic enzymes or exotoxins. Group B Streptococci have a capsule.
17. Toxins of the Streptococci:Group A Streptococci:1- Erythrogenic toxin: causes the rash in the scarlet fever. This mechanism of action is similar to that of the toxic shock syndrome toxin of staph aureus. 2- Streptolysin O: is a hemolysin that is inactivated by oxidation (oxygen-labile). It causes beta-hemolysis only when colonies grow under the surface of a blood agar. It is antigenic, and antibody to it (ASO) develop after group A Streptococcal infections. (ASO) titer is important in the diagnosis of Rheumatic fever. 3- Streptolysin S: is a hemolysin that is not inactivated by oxidation (oxygen) (oxygen-stable). It is not antigenic, but responsible for beta-hemolysis only when colonies grow under the surface of a blood agar.
18. 4- Pyrogenic exotoxin A: is the toxin responsible for most cases of Streptococcal toxic shock syndrome. It is a super antigen that causes the release of large amounts of cytokines from helper T-cells and macrophages as the same mode action for the Staphylococcal TSST.5- Exotoxin B: is a protease that rapidly destroys tissue that cause necrotizing fasciitis. Group B Streptococci: No cytotoxic enzymes or exotoxins. Group B Streptococci have a capsule.
19. Clinical Findings:- Group A Streptococci:1- Pyogenic diseases such as (Pharyngitis and Cellulitis).2- Toxigenic diseases as (Scarlet fever and Toxic shock syndrome).3- Immunologic diseases as (Rheumatic fever and acute glomerulonephritis).
20. Pyogenic diseases: S. pyogenes with Pharyngitis: is characterized by:- Inflammation, exudate, fever, leukocytosis, and tender cervical lymph nodes.- If untreated, spontaneous recovery occurs in 10 days.- It may be extend to otitis, sinusitis, mastoiditis and meningitis.- If the infection Streptococci produce (Erythrogenic toxin) and the host lacks to antitoxin lead to scarlet fever.Note: Rheumatic fever may occurs especially following Pharyngitis.
21. Cellulitis: is characterized by: - Erysipelas, necrotizing fasciitis (streptococcal gangrene), lymphangitis, or bacteremia.- Can enter the uterus after delivery to produce endometritis and sepsis (puerperal fever).- Streptococcal pyoderma (impetigo) is a superficial infection of abraded skin that forms pus.- It is communicable among children especially in hot, humid climate.- Glomerulonephritis may occur, especially following skin infections.
22. Toxigenic diseases: Scarlet fever: may result when the streptococci infection produces the erythrogenic toxin and the host lacks for the antitoxin.Toxic shock syndrome: which has the same clinical findings to those of Staphylococcal toxic shock syndrome (TSST). Immunologic diseases:Rheumatic fever: - Approximately 2 weeks after a group A streptococcal infection of the (usually pharyngitis) and rheumatic fever.Rheumatic fever: characterized by:- Fever, migratory polyarthritis, and carditis may develop.- Carditis damages myocardial and endocardial tissue, especially the mitral and aortic valves.- Uncontrollable, spasmodic movements of the limbs or face may also occur.
23. Note: - ASO titers and Erythrocyte sedimentation rare are elevated. - Group A streptococcal skin infections do not cause rheumatic fever. - If the streptococcal infections are treated within 8 days of onset, rheumatic fever is usually prevented.
24. Acute glomerulonephritis (AGN): - AGN typically occurs in 2-3 weeks after skin infection by certain group A streptococcal types in children (eg; M protein type 49 causes AGN most frequently). - AGN is more frequent after skin infection. Acute glomerulonephritis: characterized by:- Hypertension, edema of the face and ankles.- Smoky urine (due to red cells in the urine). Note: - Most patients recover completely. - Reinfection with streptococci rarely leads to recurrence of acute glomerulonephritis. - Acute rheumatic fever and the acute glomerulonephritis are known (poststreptococcal nonsuppurative diseases).
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26. Group B Streptococci: Cause Neonatal sepsis and meningitis: The main predisposing factor is prolonged (longer than 18 hr.) rupture of the membranes in women (particularly in the setting of inadequate prophylactic treatment) who are colonized with the organism.Children born prior to (37) weeks gestation have a greatly increased risk of disease (children whose mothers who lack Ab (antibody) to group B Streptococci and who consequently are born without transplacentally acquired IgG have rate of neonatal sepsis caused by this organism.Group B Streptococci are important cause of neonatal pneumonia.Group B Streptococci are also cause such infections as (Pneumonia, Endocarditis, Arthritis and Osteomyelitis) in adults The main predisposing factor for adult group B Streptococcal infections is the Diabetes.
27. Lab Diagnosis: Specimens: throat swab, pus, serum or blood. Gram- stain: gram- positive. Culture: on blood agar, incubate with 10% of CO2 for 18-24 hr. Bacitracin- sensitivity test. ASO titer (Anti-streptolysin titer): serological test, if Ab to streptolysin O is more than 200 is a significant for rheumatic fever.
28. Treatment: All group A streptococci are susceptible to penicillin G, but Rheumatic fever and Acute glomerulonephritis (AGN) patients no benefit from penicillin treatment after onset. In mild group A streptococcal infections, oral penicillin V can be used. In penicillin- allergic patients, erythromycin or one of its long- acting derivatives, eg, azithromycin can be used. However, erythromycin-resistant strains of S. pyogenes have emerged that may limit the effectiveness of the macrolide class of drugs in the treatment of streptococcal pharyngitis
29. Treatment:Endocarditis caused by most viridans streptococci is curable by prolonged penicillin treatment.Group B Streptococci infections treated by penicillin G or ampicillin. But some strains are resistant will require to higher doses of penicillin G or a combination of penicillin G and an aminoglycoside to eradicate the organism.Group D streptococci, eg, S. bovis can be treated with penicillin G.
30. Control: Detection of respiratory and skin infection.Prompt penicillin treatment of streptococcal pharyngitis reduces the antigenic stimulus and therefore prevents glomerulonephritis and acute rheumatic fever. Prevention of streptococcal infections (usually with benzathine penicillin once each months for several years) in persons who have had rheumatic fever is important to prevent recurrence of the disease.
31. References:-Jawetz, Melnick & Adelberg’s, 2019. Medical Microbiology,28th Edition. The McGraw-Hill education, Inc. USA.- Levinson, W.E., 2018. Review of medical microbiology and immunology. McGraw-Hill Education.
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