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Streptococci In medical microbiology and health
- 1. 1 Streptococci (Gram positive cocci) Dr Marianne Mureithi marianne@uonbi.ac.ke : @docmureithi
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- 4. Learning Objectives 4 By the end of this lecture, you will be able to: •Classify Streptococci by hemolysis patterns and Lancefield grouping •Identify key pathogenic Streptococci species & describe their disease associations. •Explain the pathogenesis of Streptococcal infections •Diagnose Streptococcal infections using a combination of clinical presentation, laboratory diagnostics, •Discuss treatment strategies and prevention including antibiotic selection, resistance challenges, and the role of vaccines in managing Streptococcal diseases.
- 5. Streptococci • Morphology: Gram-positive cocci approximately 1µm in diameter. • Arrangement: Occur in chains or pairs. • Capsule: Often encapsulated, contributing to virulence. • Mobility: Non-motile. • Spore Formation: Do not form spores. • Respiration: Facultative anaerobes, can survive with or without oxygen. • Enzyme Activity: Catalase-negative; unlike Staphylococci, they cannot decompose hydrogen peroxide.
- 6. Classification of Streptococci • Streptococci can be classified according to: – Serology (Lanciefield Classification) – Hemolysis on Blood Agar (BA)
- 7. Serology: Lanciefield Classification Streptococci Group A S. pyogenes Group B S. agalactiae Group C S. equisimitis Group D Enterococcus Other groups (E-U) Lanciefield classification
- 8. Hemolysis on Blood agar -hemolysis -hemolysis -hemolysis
- 9. Classification of Streptococci Based on Hemolysis on Blood Agar Hemolysis on BA – -hemolysis Partial hemolysis Green discoloration around the colonies- Iron oxidation e.g. non-groupable streptococci (S. pneumoniae & S. viridans) – -hemolysis Complete hemolysis Clear zone of hemolysis around the colonies e.g. Group A & B (S. pyogenes & S. agalactiae) – -hemolysis No lysis e.g. Group D (Enterococcus spp) Streptococci -hemolysis -hemolysis -hemolysis
- 10. 10 Beta hemolytic Group A Streptococcus (GAS) 1
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- 12. Group A Streptococci(GAS) Streptococcus pyogenes: • Basic Characteristics: • Gram-positive cocci in chains or pairs. • Epidemiology: • Commonly found in the throat and on the skin. • Can be carried asymptomatically. • Pathogenicity: • Produces a wide range of virulence factors, including M proteins, streptolysins, and exotoxins. • Causes both suppurative (pus-forming) and non-suppurative (post-infectious) diseases. • Clinical Diseases: • Suppurative: Pharyngitis (strep throat), impetigo, cellulitis, and necrotizing fasciitis. • Non-suppurative: Rheumatic fever and acute glomerulonephritis following infection. • Treatment and Management: • Typically sensitive to penicillin; antibiotic treatment is effective for most acute infections. • Post-infection sequelae require long-term management and can lead to chronic conditions. • .
- 13. Data obtained from a Centers for Disease Control and Prevention Active Bacterial Core Surveillance Report for group A streptococcal Who is at Risk for Infection?
- 14. Clinical conditions 1. Pyogenic – Pharyngitis, tonsillitis, peritonsillar abscess, sinusitis, otitis media, impetigo, wound infection, osteomyelitis, septic arthritis, puerperal sepsis, bacteraemia, acute bacterial endocarditis 2. Toxigenic(exotoxins) – Scarlet fever – Streptococcal toxic shock syndrome 3. Immune-mediated: non-suppurative – Occurs after repeated infections – AGN- Acute glomerulonephritis-follows skin – ARF- Acute rheumatic fever. Cross reactivity of the antibodies produced during streptococcal pharyngitis, cross react with antigens in heart muscle
- 17. Strep throat - hemolytic - Group A (GAS) streptococci: S. pyogenes Droplet Transmission Symptoms: Sore throat, high fever, coughing, otitis media may also occur
- 18. Complications of Strep Throat S. pyogenes causes two major autoimmune complications (antibodies cross-react) 1. Acute rheumatic fever: Short period of arthritis and fever followed in 50% of affected by rheumatic heart disease heart valve damage chronic valvular disease (stenosis and/or incompetence) heart failure and/or subacute bacterial endocarditis 2. Acute poststreptococcal glomerulonephritis
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- 20. Laboratory diagnosis • Specimen: Throat swabs, pus swabs, blood, CSF etc • Direct Gram stain- Gram-positive cocci in chains, pus cells • Culture: – BA, aerobically, 37°C for 18-24 hours – Smooth circular colonies of 2-3 mm diameter, β- haemolysis • Gram-positive cocci in chains • Catalase negative • Bacitracin sensitive
- 21. Treatment and Prevention Treatment – Cephalosporins – Tetracyclines – Erythromycin – Chloramphenicol Prevention – Infection control – Treat pharyngitis as early as possible to prevent ARF – No vaccine
- 22. VACCINES • Research focuses on M protein-based, multivalent, recombinant, and universal antigen vaccines for broad immunity. • Clinical trials underway; major challenges include preventing autoimmune reactions and ensuring global vaccine accessibility. 22
- 23. Group B Streptococci(GBS) Streptococcus agalactiae • Classification: Belongs to Group B of the Lancefield classification. • Morphology: Gram-positive cocci, usually in chains. • Habitat: Colonizes the gastrointestinal and genitourinary tracts of humans. • Virulence Factors: Capsular polysaccharide, C5a peptidase, hemolysins, and sialic acid-rich surface proteins contribute to its evasion of the immune system and pathogenicity.
- 24. Clinical manifestations • Pathogenicity: • In Neonates: Leading cause of neonatal sepsis, meningitis, and pneumonia. • In Adults: Can cause urinary tract infections, skin and soft-tissue infections, and, in pregnant women, chorioamnionitis and postpartum infections. Early onset neonatal disease(1st 7 days of life)- – Vertical transmission in utero or at time of delivery Late onset(7-90 days)- nosocomial/vertical
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- 27. Lab diagnosis – Group B Streptococci • Specimens: CSF, blood, vaginal smears, urine • Microscopy :Gram stain - GPC in chains • Culture: BA - beta hemolytic colonies • Identification tests – Catalase negative – Bacitracin resistance – CAMP Test + – Penicillin sensitive P B
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- 29. VACCINE 2 Group B streptococcal vaccine - This vaccine is currently under development
- 30. 30 Alpha hemolytic streptococci Streptococcus pneumoniae 1
- 31. INTRODUCTION: • Common name Pneumococcus. • Has over 100 Serotypes • Normal inhabitants of the upper respiratory tract of human beings. • Gram positive small(1μm), slightly elongated cocci, with one end broad & other end pointed, presenting a flame shaped or lanceolate appearance.
- 32. Disease: 1. Otitis media & sinusitis 2. Pneumonia a. Lobar pneumonia b. Bronchopneumonia 3. Tracheobronchitis 4. Meningitis 5. Other infections- empyema, pericarditis, conjunctivitis, suppurative arthritis & peritonitis.
- 33. 33 Marianne W. Mureithi, et al; T Cell Memory Response to Pneumococcal Protein Antigens in an Area of High Pneumococcal Carriage and Disease, The Journal of Infectious Diseases, Volume 200, Issue 5, 1 September 2009, Pages 783– 793, https://doi.org/10.1086/605023 MOC Ota,, MW Mureithi, et al: Antibody and T-cell responses during acute and convalescent stages of invasive pneumococcal disease Adam Finn, Marianne W. Mureithi, et al. Evolution of Naturally Acquired T-Cell Immunity to Pneumococcal Protein Antigens in Infants from an Area of High Pneumococcal Carriage & Disease. Infectious Diseases Society of America (IDSA) 2008
- 34. Virulence • Capsular polysaccharide- antiphagocytic • IgA1 protease • Pneumolysins – Slows ciliary beating – Toxic to pulmonary endothelial cells – Spread of organism from alveoli into bloodstream • Autolysin – Breaks the peptide cross-linking of the cell wall peptides leading to cell lysis
- 35. 35 Lab diagnosis • Specimen: CSF, blood, sputum, pus, swabs • Microscopy: Gram stain – GPC in pairs, capsulated, lanceolate shaped • Culture – BA – alpha hemolytic colonies • Identification tests – Catalase –ve – Optochin sensitive – Bile solubility – Quellung reaction
- 36. Optochin sensitivity: Sensitive. Quellung( capsular swelling ) reaction Bile Solubility
- 37. Treatment and Prevention Treatment • Penicillins, ampicillin- resistance increasing • Ceftriaxone, cefotaxime, carbapenems, fluoroquinolones, erythromycin, chloramphenicol, vancomycin Prevention • Vaccine
- 38. Conjugate Vaccine • A new generation of pneumococcal vaccines • Coating removal of the capsular polysaccharide • 7 (9, 11 or 13) types of saccharide is separately activated and conjugated to protein carrier • CDC recommended PVC vaccine schedule: 2mo, 4mo, 6mo, 12-15mo, 65years
- 39. LATEST NEWS • FDA Approval: PREVNAR 20™, a 20-valent pneumococcal conjugate vaccine by Pfizer, approved by the U.S. FDA. • Coverage: Provides protection against 20 serotypes of pneumococcus responsible for most invasive pneumococcal disease and pneumonia. • Significance: Includes seven serotypes linked to 40% of pneumococcal disease • Advancement: Represents a significant advancement in pneumococcal disease prevention, offering broader protection than previously available vaccines. 40
- 41. Viridans Streptococci • Normal flora of oral cavity, nasopharynx, genital tract and skin • S.mitis • S.mutans • S.milleri • S.salivarius • S.sanguis unique ability to synthesize dextrans from glucose, which allows them to adhere to fibrin-platelet aggregates at damaged heart valves. extraction).
- 42. Clinical manifestations • Dental caries • Gingivitis, pyogenic oral infections • Subacute bacterial endocarditis • Brain abscesses, abdominal abscesses
- 43. Laboratory diagnosis • Specimen: blood, pus • Gram stain- Gram-positive cocci in chains • Culture on BA – Incubate in air at 37°C for 18-24 hours • Biochemical tests – Catalase negative – Optochin resistant – bile insoluble • Molecular studies e.g. PCR
- 44. Treatment • Prophylaxis to patient at risk during dental surgery • Penicillin and other β-lactam • Ampicillin and Gentamicin • Vancomycin- for penicillin allergies
- 46. 47 Group D Streptococcus- Gamma Hemolytic Normal flora in GIT, lower genital tract Nosocomial / opportunistic pathogen Enterococcus – 2 imp. species E. fecalis E. faecium UTI, wound infection, endocarditis Resistance to cephalosporins, even vancomycin 1
- 47. Points to Remember/Conclusion • Diversity and Classification: Streptococci, a diverse genus of Gram- positive bacteria, classified by hemolysis, Lancefield groups. • Major Pathogens: Includes Group A (S. pyogenes) causing rheumatic fever, and Group B (S. agalactiae) linked to neonatal sepsis. • Virulence & Diseases: Equipped with virulence factors (e.g., M protein, hyaluronic acid) causing diseases from pharyngitis to severe infections. • Diagnosis & Treatment: Diagnosed via culture, antigen detection; treated with antibiotics, with emphasis on resistance management. • Prevention & Research: Hygiene, antibiotics, pneumococcal vaccines critical; ongoing research into GAS vaccines and new treatments. • Global Impact: significant health challenge, requiring ongoing vigilance and innovative control strategies.