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Strep pneumoniae


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Strep pneumoniae

  1. 1. DR KAMRAN AFZAL ASST PROF MICROBIOLOGY Streptococcus pneumoniae
  2. 2. Gram positive cocci Catalase Negative Streptococci (Chains) Catalase Positive Staphylococci (Clusters) Haemolysis on Blood agar Alpha or incomplete Strept pneumoniae Or viridans Beta or complete Gropu A, B, C, D Coagulase
  3. 3. The Genus Streptococcus <ul><li>FAMILY Streptococcaceae </li></ul><ul><li>Some important pathogens, commensals of mucous membranes </li></ul><ul><li>Opportunistic pathogens </li></ul><ul><li>40 species, in 6 clusters </li></ul><ul><li>Strong fermenters of carbohydrates -> Lactic acid </li></ul><ul><li>Facultative anaerobes </li></ul><ul><li>Peptostreptococci are obligate anaerobe S </li></ul>
  4. 4. Clinically Important Streptococci Group Species Lancefield Group Type of Haemolysis Pyogenic S. pyogenes S. agalactiae S. eqisimilus A B C β β β Mitis S. pneumoniae S. mitis S. sanguis O O H α α α Anginosus S. anginosus G, F α Salivarius S. salivarius K γ Bovis S. bovis D α Mutans S. mutans No γ
  5. 5. Haemolytic Activity <ul><li>β Haemolysis </li></ul><ul><ul><li>Complete lysis/clearing of RBCs induced by bacterial haemolysins </li></ul></ul><ul><li>α Haemolysis </li></ul><ul><ul><li>Incomplete haemolysis of RBCs </li></ul></ul><ul><ul><li>H 2 O 2 oxidizes Hb -> Methaemoglobin (greenish) </li></ul></ul><ul><li>γ Haemolysis </li></ul><ul><ul><li>No </li></ul></ul><ul><ul><li>haemolysis </li></ul></ul>
  6. 6. Strep pneumoniae <ul><li>Morphology </li></ul><ul><li>Gram positive lancet shaped diplococci arranged in pairs </li></ul><ul><li>In body fluids in addition we may see it singly or in short chains </li></ul>
  7. 7. <ul><li>Antigenic Structure </li></ul><ul><li>The organism is capsulated with 90 different capsular polysaccharide types </li></ul><ul><ul><ul><li>Elicits humoral response - formation of antibodies </li></ul></ul></ul><ul><li>The cell wall contains another polysaccharide that is common to all pneumococci </li></ul><ul><li>C- Substance that binds to C-reactive protein </li></ul>
  8. 8. Virulence Factors <ul><li>Polysaccharide capsule - the major virulence factor </li></ul><ul><ul><li>It prevents phagocytosis by host immune cells </li></ul></ul><ul><li>Autolysin </li></ul><ul><ul><li>Activation of this protein lyses the bacteria -> Pneumolysin </li></ul></ul><ul><li>Pneumolysin </li></ul><ul><ul><li>Lyses host cells of immune system </li></ul></ul><ul><ul><li>Facilitates colonization </li></ul></ul><ul><li>M-protein </li></ul><ul><ul><li>Antiphagocytic </li></ul></ul><ul><li>Lipoteichoic acid </li></ul><ul><ul><li>Activates complement </li></ul></ul><ul><li>IgA protease </li></ul><ul><ul><li>Helps in colonization </li></ul></ul>
  9. 9. Predisposing Factors <ul><li>Alcohol or drug intoxication </li></ul><ul><li>Immunocompromised </li></ul><ul><li>Elderly </li></ul><ul><li>Abnormality of the respiratory tract </li></ul><ul><ul><li>Viral infections, bronchial obstruction and respiratory tract injury </li></ul></ul><ul><li>Abnormal circulatory dynamics </li></ul><ul><li>Splenectomy </li></ul><ul><li>Chronic diseases </li></ul><ul><ul><li>Sickle cell anaemia </li></ul></ul>
  10. 10. Transmission And Colonisation
  11. 11. Pathogenesis
  12. 12. Diseases Caused <ul><li>Non-invasive disease </li></ul><ul><li>Sinusitis (sinuses) </li></ul><ul><li>Otitis media (middle ear) </li></ul><ul><li>Pneumonia (lungs) </li></ul><ul><li>Invasive disease </li></ul><ul><li>Bacteraemia (blood) </li></ul><ul><li>Meningitis (CNS) </li></ul><ul><li>Endocarditis (heart) </li></ul><ul><li>Peritonitis (body cavity) </li></ul><ul><li>Septic arthritis (bones and joints) </li></ul><ul><li>Others (appendicitis, salpingitis, soft-tissue infections) </li></ul>PNEUMOCOCCAL INFECTION Pneumonia
  13. 13. Pneumococcal Disease Wenger et al., J Infect Dis, 1990 Pathogenic agents in bacterial meningitis in persons aged  60 years in the USA Others 26% Streptococcus pneumoniae 49% Group B streptococcus 3% Haemophilus influenzae 4% Neisseria meningitidis 4% Listeria monocytogenes 14%
  14. 14. Clinical Features Septicemia Pneumonia Fever Hypotension Acute confusion Chills Dyspnea Tachypnea Headache Tachycardia Fever Dyspnea Lung consolidation Hemoptysis chills Chest pain Cyanosis malaise Rust colored sputum
  15. 15. Pneumonia <ul><li>Complications </li></ul><ul><ul><li>Bacteraemia in 15  20% of patients </li></ul></ul><ul><ul><li>high mortality despite appropriate antibiotic therapy </li></ul></ul><ul><ul><li>overall case fatality rate 15-20% </li></ul></ul><ul><ul><li>higher case fatality rates (30-40%) for elderly </li></ul></ul><ul><ul><li>Spread of pneumococci in the blood to other normally sterile sites can cause other invasive pneumococcal diseases (e.g. meningitis) </li></ul></ul><ul><ul><li>Empyema (pus in the pleural cavity) in about 2% of cases </li></ul></ul>
  16. 16. Lab Diagnosis <ul><li>Specimens </li></ul><ul><li>Sputum </li></ul><ul><li>Blood </li></ul><ul><li>CSF </li></ul><ul><li>Swabs </li></ul><ul><li>Urine </li></ul><ul><li>Inoculation </li></ul><ul><li>Blood, chocolate agar at 37 o C for 24-48 hrs </li></ul>
  17. 17. Cultural Characteristics <ul><li>No growth on simple media </li></ul><ul><li>Grow well on enriched media like blood agar </li></ul><ul><li>Grow better in 5-10% CO 2 </li></ul><ul><li>The colonies are alpha haemolytic, 1-2 mm </li></ul><ul><ul><li>Have the tendency to undergo autolysis </li></ul></ul><ul><ul><li>They collapse in the centre and raised at the periphery giving ‘Draughtsman’s’ colonies appearance </li></ul></ul>
  18. 18. <ul><li>In addition to alpha haemolysis, this strain of Streptococcus pneumoniae is producing abundant polysaccharide capsular material evidenced by the mucoid or &quot;oil droplet&quot; appearance on the colonies </li></ul>
  19. 19. Identification <ul><li>Gram staining </li></ul><ul><li>Catalase negative </li></ul><ul><li>Alpha haemolysis </li></ul><ul><li>Soluble in bile salts </li></ul><ul><li>Sensitivity to optochin </li></ul><ul><li>Capsular swelling </li></ul><ul><li>(Quellung reaction) </li></ul><ul><li>Antigen detection </li></ul><ul><li>Animal pathogenicity </li></ul><ul><li>Molecular typing </li></ul>
  20. 20. <ul><li>Gram Staining (Direct microscopy) </li></ul><ul><li>Lancet (lanceolate) shaped diplococci having long axis in line with each other </li></ul><ul><li>Pus cells are also present </li></ul>
  21. 21. <ul><li>Alpha haemolysis </li></ul>
  22. 22. <ul><li>Optochin sensitivity </li></ul>16 mm
  23. 23. <ul><li>Capsular Swelling Reaction </li></ul><ul><li>If sputum or specimen mixed with a polyvalent antiserum and then stained, the capsule increases in size </li></ul><ul><ul><li>The Quellung test is used in pneumococcus typing </li></ul></ul>
  24. 24. <ul><li>Bile solubility </li></ul><ul><li>The organisms are rapidly lysed by surface active chemicals like bile salts </li></ul>
  25. 25. <ul><li>Antigen Detection </li></ul><ul><li>Capsular polysaccharide antigen </li></ul><ul><li>In serum, CSF or Urine </li></ul><ul><li>By latex agglutination method </li></ul><ul><li>Rapid method </li></ul><ul><li>Useful to diagnose bacteraemia and meningitis </li></ul>
  26. 26. <ul><li>Animal pathogenicity </li></ul><ul><li>Intraperitoneal injection of the organisms </li></ul><ul><li>The animal dies and the microorganisms can be isolated from blood </li></ul>
  27. 27. <ul><li>Molecular typing </li></ul><ul><li>PCR </li></ul><ul><li>RFLP </li></ul><ul><li>DNA sequencing </li></ul>
  28. 28. <ul><li>Sensitivity testing </li></ul>
  29. 29. Treatment <ul><li>Penicillins, tetracylines and macrolides </li></ul><ul><ul><li>They have remained sensitive over the years </li></ul></ul><ul><ul><li>Resistant strains are being reported </li></ul></ul><ul><li>Ceftriaxone for the resistant strains </li></ul><ul><li>Vancomycin for ceftriaxone resistant strains </li></ul>
  30. 30. Pneumococcal Vaccine <ul><li>90 different capsular types </li></ul><ul><li>23-valent pneumococcal vaccine contains purified capsular polysaccharides </li></ul><ul><li>Serotype coverage 2,3 </li></ul><ul><ul><li>85-90% of serotypes responsible for all cases of invasive pneumococcal disease </li></ul></ul><ul><ul><li>Vaccine includes major serotypes that have developed antimicrobial resistance </li></ul></ul>
  31. 31. Case History <ul><li>A 53 year-old man with non-insulin-dependent diabetes </li></ul><ul><li>Presents with symptoms of fever, chills and cough with rust colored sputum for 05 days </li></ul><ul><li>Pulse of 110/min, Fever 103 0 F </li></ul><ul><li>Crackles in right lung field along with decreased air entry on respiratory examination </li></ul>
  32. 32. X-ray chest
  33. 33. Sputum Gram’s Stain
  34. 34. Culture
  35. 35. Susceptible to Optochin
  36. 36. Sensitivity testing
  37. 37. <ul><li>Causative agent is Streptococcus Pneumoniae </li></ul><ul><li>It is the only strep that is susceptible to Optochin </li></ul>
  38. 38. Special technique..