Streptococci

Streptococci

اسلاید 1: StreptococciCharacters of StreptococciGram positive cocci1µm in diameterChains or pairsUsually capsulatedNon motileNon spore formingFacultative anaerobesFastidiousCatalase negative (Staphylococci are catalase positive)

اسلاید 2: Classification of StreptococciStreptococci can be classified according to:Oxygen requirementsAnaerobic (Peptostreptococcus)Aerobic or facultative anaerobic (Streptococcus)Serology (Lanciefield Classification)Hemolysis on Blood Agar (BA)

اسلاید 3: Serology: Lanciefield ClassificationStreptococci classified into many groups from A-K & H-VOne or more species per groupClassification based on C- carbohydrate antigen of cell wallGroupable streptococciA, B and D (more frequent)C, G and F (Less frequent)Non-groupable streptococciS. pneumoniae (pneumonia)viridans streptococcie.g. S. mutansCausing dental carries

اسلاید 4:

اسلاید 5: Classification of Streptococci Based on Hemolysis on Blood AgarHemolysis on BA-hemolysisPartial hemolysisGreen discoloration around the coloniese.g. non-groupable streptococci (S. pneumoniae & S. viridans)-hemolysisComplete hemolysisClear zone of hemolysis around the coloniese.g. Group A & B (S. pyogenes & S. agalactiae)-hemolysisNo lysise.g. Group D (Enterococcus spp)

اسلاید 6: Hemolysis on Blood agar-hemolysis-hemolysis-hemolysis

اسلاید 7: Group A streptococciInclude only S. pyogenesGroup A streptococcal infections affect all ages peak incidence at 5-15 years of age90% of cases of pharyngitis

اسلاید 8: Pathogenesis and Virulence FactorsStructural componentsM protein M, which interferes with opsonization and lysis of the bacteriaLipoteichoic acid & F protein adhesionHyaluronic acid capsule, which acts to camouflage the bacteriaEnzymesStreptokinasesDeoxynucleases C5a peptidasePyrogenic toxins that stimulate macrophages and helper T cells to release cytokinesStreptolysinsStreptolysin O lyse red blood cells, white blood cells, and plateletsStreptolysin Sfacilitate the spread of streptococci through tissue