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II - Streptococci

II - Streptococci. Characters of Streptococci. Gram positive cocci Chains or pairs Usually capsulated Non motile Non spore forming Facultative anaerobes Fastidious Catalase negative (Staphylococci are catalase positive). Classification of Streptococci:

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II - Streptococci

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  1. II- Streptococci Characters of Streptococci Gram positive cocci Chains or pairs Usually capsulated Non motile Non spore forming Facultative anaerobes Fastidious Catalase negative (Staphylococci are catalase positive)

  2. Classification of Streptococci: Streptococci can be classified according to:

  3. Serology (Lanciefield Classification) **There are 20 described serotypes, named Lancefield groups A to V, which describes specific carbohydrates present on the bacterial cell wall. **Lancefield groups A and B include the significant streptococcal pathogens of humans Beta hemolytic streptococci **There is Non-groupable streptococci ; S. pneumoniae (pneumonia) and viridans streptococci

  4. Hemolysis on Blood Agar (BA) Alpha-hemolysis Partial hemolysis Green discoloration around the colonies e.g. non-groupable streptococci (S. pneumoniae & S. viridans)

  5. Beta-hemolysis Complete hemolysis Clear zone of hemolysis around the colonies e.g. Group A & B (S. pyogenes & S. agalactiae)

  6. Gamma-hemolysis No lysis e.g. Group D (Enterococcus spp)

  7. Experimental: 1- Gram stain of streptococci 2- Catalase 3- Hemolysis on blood agar (alpha, Beta, and Ghama hemolysis) 4- Bacitracin susceptibility test 5- Optochin susceptibility test

  8. Macroscopical Examination

  9. Catalase Test

  10. Growth on Blood Agar Sterptococci are divided into three main groups accorging to its action on erythrocytes: β-hemolytic Sterptococci\ α-hemolytic Sterptococci. γ-hemolytic Sterptococci. β-hemolytic Sterptococci Definitive test to differentiate between S.Pyogenes & Non group A β-hemolytic Streptococci

  11. Growth on Blood Agar β-hemolytic Sterptococci:  It causes complete hemolysis to RBCs leading to formation of clear zone around the colonies Example: Strept. Pyogenes (group A β-hemolytic Strept.)

  12. Bacitracin Sensitivity Test: ***Differentiation between Beta-hemolytic streptococci Definitive test to differentiate between S.Pyogenes & Non group A β-hemolytic Streptococci Principle: A low conc. of Bacitracin (0.04 units) will selectively inhibit the growth of S.pyogenes giving a zone of inhibition around the disc

  13. Procedure: Inoculate blood agar plate with the test organism. . Aseptically apply Bacitracin disc onto the center of the streaked area Incubate the plate at 35oC for 18 hrs Results: Positive test: any zone of inhibition around the disc.

  14. CAMP test Principle: –Group B streptococci produce extracellular protein (CAMP factor) –CAMP act synergistically with staph. -lysin to cause lysis of RBCs Procedure: –Single streak of Streptococcus to be tested and a Staph. aureus are made perpendicular to each other –3-5 mm distance was left between two streaks –After incubation, a positive result appear as an arrowhead shaped zone of complete hemolysis –S. agalactiae is CAMP test positive while non gp B streptococci are negative Manal Al

  15. Pathogenesis and Virulence Factors Group A streptococci Structural components 1-M protein M 2- Lipoteichoic acid & F protein 3-Hyaluronic acid capsule, which acts to camouflage the bacteria Enzymes Streptokinases Deoxynucleases C5a peptidase Pyrogenic toxins Streptolysins Streptolysin O lyse red blood cells, white blood cells, and platelets Streptolysin S Group A streptococci

  16. α-hemolytic Sterptococci: It causes: 1. Partial hemolysis to RBCs. 2. Act enzymatically on blood pigment leading to green discoloration around the colonies. Example: Strept. Pneumonia, viridans Streptococci.

  17. Optochin Sensitivity Test: Result: (+)Positive test: inhibition zone more than 15 mm in diameter. Optochin sensitive S.pneumoniae (+) Optochin resistant Viridans Streptococci (-)

  18. α-hemolytic Sterptococci 2. Bile Solubility Test: Principle: S.Pneumoniae produce a self-lysing enzyme to depress the growth of old colonies. The presence of bile salt accelerate this process.

  19. α-hemolytic Sterptococci Procedure: 1-10 ml broth culture of the test organism 2- Add 1 ml 10% bile salt solutio 3. Incubate at 37oC for 15 min . 4- Observe for the visible clearing of the turbid culture.

  20. α-hemolytic Streptococci 2. Bile Solubility Test Results: Positive test: Visible clearance of the turbid culture Visible clearance S.Pneumoniae Remain turbid Viridans Streptococci

  21. γ-hemolytic Sterptococci Definitive test for Enterococcusfaecalis Growth on MacConkey’s agar: Results: Growth on MacConkey’s agar: No Growth Growth of pink colonies (Enterococcus faecalis) Other Strain of Sterptococci

  22. Practical Work 1-Gram’s Stain (spots) 2.Catalase test 3.Blood agar plate. 4.Bacitracin & Optochin Sensitivity. 5.MacConkey’s agar plate.

  23. γ-hemolytic Sterptococci: It has no effect on RBCs (Non hemolytic Sterptococci)  Example: Enterococcusfaecalis

  24. Optochin Sensitivity Test: ***Differentiation between Alpha-hemolytic streptococci Definitive test to differentiate between S.Pneumoniae & Viridans Streptococci Principle S.Pneumoniae is inhibited by less than 5 μg/ml Optochin reagent giving a zone of inhibition more than 15 mm in diameter. Procedure: 1. Inoculate blood agar plate with the test organism. 2. Aseptically apply Optochin disc onto the center of the streaked area. 3. Incubate the plate at 35oC for 18 hrs. 4. Accurately measure the diameter of the inhibition zone around the disc.

  25. ***Definitive test for Enterococcusfaecalis (Gamma hemolytic streptococci Growth on MacConkey’s agar: ****Principle: MacConkey’s agar is a selective medium for Gram’s –ve bacteria. It contains bile salt and crystal violet to inhibit the growth of Gram’s +ve bacteria. Enterococcus faecalis is the only Streptococcus species which can grow on MacConkey’s agar giving pink colonies.

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