Bài giảng Vi khuẩn học chuyên khoa - Streptococci

Nội dung text: Bài giảng Vi khuẩn học chuyên khoa - Streptococci

1. Disease caused by S. pyogenes • Suppurative (sự sinh mủ) • Non-Invasive • Pharyngitis (“strep throat”)-inflammation (viêm họng) of the pharynx • Skin infection, Impetigo (bệnh chốc lở) • Invasive • Scarlet fever-rash (sốt ban đỏ) that begins on the chest and spreads across the body • Pyoderma-confined, pus-producing lesion (viêm da mủ) that usually occurs on the face, arms, or legs • Necrotizing fasciitis-toxin production (độc tố gây viêm cơ da hoại tử) destroys tissues and eventually muscle and fat tissue • Non Suppurative • Rheumatic fever (sốt thấp khớp): Life threatening inflammatory disease that leads to damage of heart valves muscle • Glomerulonephritits (viêm tiểu cầu thận) • Immune complex disease of kidney • inflammation of the glomeruli and nephrons which obstruct blood flow through the kidneys
2. Differentiation between -hemolytic streptococci • The following tests can be used to differentiate between -hemolytic streptococci • Lanciefield Classification • Bacitracin susceptibility Test • Specific for S. pyogenes (Group A) • CAMP test • Specific for S. agalactiae (Group B)
3. Bacitracin sensitivity • Principle: • Bacitracin test is used for presumptive identification of group A • To distinguish between S. pyogenes (susceptible to B) & non group A such as S. agalactiae (Resistant to B) • Bacitracin will inhibit the growth of gp A Strep. pyogenes giving zone of inhibition around the disk • Procedure: • Inoculate BAP with heavy suspension of tested organism • Bacitracin disk (0.04 U) is applied to inoculated BAP • After incubation, any zone of inhibition around the disk is considered as susceptible
4. 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
5. CAMP test
6. Differentiation between -hemolytic streptococci • The following definitive tests used to differentiate between S. pneumoniae & viridans streptococci • Optochin Test • Bile Solubility Test • Inulin Fermentation
7. Optochin Susceptibility Test • Principle: • Optochin (OP) test is presumptive test that is used to identify S. pneumoniae • S. pneumoniae is inhibited by Optochin reagent (<5 µg/ml) giving a inhibition zone ≥14 mm in diameter. • Procedure: • BAP inoculated with organism to be tested • OP disk is placed on the center of inoculated BAP • After incubation at 37oC for 18 hrs, accurately measure the diameter of the inhibition zone by the ruler • ≥14 mm zone of inhibition around the disk is considered as positive and ≤13 mm is considered negative • S. pneumoniae is positive (S) while S. viridans is negative (R)
8. Optochin Susceptibility Test Optochin resistant S. viridans Optochin susceptible S. pneumoniae
9. Bile Solubility test • Principle: • S. pneumoniae produce a self-lysing enzyme to inhibit the growth • The presence of bile salt accelerate this process • Procedure: • Add ten parts (10 ml) of the broth culture of the organism to be tested to one part (1 ml) of 2% Na deoxycholate (bile) into the test tube • Negative control is made by adding saline instead of bile to the culture • Incubate at 37oC for 15 min • Record the result after 15 min
10. Bile Solubility test • Results: • Positive test appears as clearing (trong) in the presence of bile while negative test appears as turbid (đục) • S. pneumoniae soluble (hòa tan) in bile whereas S. viridans insoluble
11. Differentiation between -hemolytic streptococci Hemolysis Bacitracin CAMP test sensitivity S. pyogenes  Susceptible Negative S. agalactiae  Resistant Positive Differentiation between -hemolytic streptococci Hemolysis Optochin Bile Inulin sensitivity solubility Fermentation S. pneumoniae Sensitive Soluble Not ferment (≥ 14 mm) Viridans strep Resistant Insoluble Ferment (≤13 mm)
12. Outline of differentiation between Gram-Positive cocci e.g. S. epidermidis