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    Microbiology   lec4 Microbiology lec4 Presentation Transcript

    • Medical Microbiology Lecture 3 Dr. Saleh M Y OTH PhD Medical Molecular Biotechnology and Infectious Diseases 02/10/2010 IMS - MSU Systemic Bactreiology
    • STREPTOCOCCI Systemic Bactreiology
    • Words must to be known
      • Group A streptococcus (S. pyogenes )
      • Lancefield groups
      • Hemolysis (alpha, beta, gamma)
      • Bacitracin susceptibility test
      • M, T, R proteins
      • Streptolysins O and S
      • F protein/lipoteichoic acid
      • Rheumatic fever/carditis/arthritis
      • Glomerulonephritis
      • Scarlet fever
      • Toxic shock-like syndrome/bacteremia
      • “ Flesh-eating bacteria”
      • Pyrogenic toxin
      • Erythrogenic toxin
      • Group B streptococcus ( S.agalactiae )
      • Neonatal septicemia/meningitis
      • CAMP test
      • Hippurate hydrolysis test
      • Group D streptococcus
      • Urinary tract infection/ endocarditis
      • Bile-esculin test
      • Enterococci
      • Non-enterococci
      • Large colony
      • Minute colony
      • Viridans streptococci
      • Dental caries/endocarditis
    • Streptococcus pyogenes During the infection, this bacteria produce pus
      • - One of the most important pathogens
      • - Gram positive cocci in chains
      • - Lancefield Serological Group A
      • - Beta Hemolytic on blood agar
    • Gram Stain of S. pyogenes Streptcoccus pyogenes S. agalactia S. peumoniae
    • Hemolysis on Blood Agar Plates
      • Beta hemolysis -organisms excretes potent hemoysins which completely lyse RBCs (complete hemolysis) thus a clear zone appears around colony. S. pyogenes
      • Alpha hemolysis -organism excretes hemolysins which partially break down rbc (incomplete hemolysis) thus a greenish zone appears around colony. S. pneumoniae
    • S.pyogenes S. pneumonia Beta hemolysis Alpha hemolysis
      • Streptococci
        • facultative anaerobe
        • Gram-positive
        • chains or pairs
        • catalase negative
      • (staphylococci are catalase positive)
      Streptococcus in chains (Gram stain)
      • Streptococci
        • Lancefield groups
          • one or more species per group
          • carbohydrate antigens
    • Groupable streptococci
      • 1- A, B and D
        • frequent
      • 2- C, G, F
        • less frequent
    • Non-groupable
      • 1- S. pneumoniae
        • pneumonia
      • 2- viridans streptococci
        • e.g. S. mutans
          • dental caries
    • hemolysis reaction - sheep blood agar
      • a- (beta- β )
        • complete clearing
        • A and B
      • b- (alpha- α )
        • partial hemolysis
          • green color
      • c- (gamma- δ )
        • no lysis
      White colonies
    • Hemolysis
      • 1- Groups A an B
        • β -hemolysis
      • 2- Group D
      • α or δ -hemolysis
      • 3- S. pneumoniae and S. viridans
        • α -hemolysis
    • hemolysis reaction + one characteristic presumptive identification
    • Group A streptococcus ( S. pyogenes ) Group A streptococcal infections affect all ages peak incidence at 5-15 years of age
    • S. pyogenes – suppurative
      • 1- non-invasive
        • - pharyngitis
        • - skin infection, impetigo
      • 2- invasive bacteremia
        • - toxic shock-like syndrome
        • - "flesh eating" bacteria
        • - pyrogenic toxin
    • Pyrogenic toxin
      • Streptococcus pyogenes and Staphylococcus aureus express pyrogenic toxin superantigens (PTSAgs) that are associated with toxic shock syndrome (TSS) and staphylococcal food poisoning (SFP).
      • Most PTSAgs cause TSS in deep-tissue infections, whereas only TSS toxin 1 (TSST-1) is associated with menstrual, vaginal TSS.
      • In contrast, SFP has been linked only with staphylococcal enterotoxins (SEs).
    • Pyrogenic toxin …
      • Because of the differential abilities of PTSAgs to cause systemic or localized symptoms in a site-dependent manner, these toxins have abilities to cross mucosal barriers.
      • The activity of three PTSAgs when delivered orally , vaginally , or intravenously to rabbits and orally to monkeys in some experimental studies.
    • Pyrogenic toxin
      • 1- superantigen
      • 2- T cell mitogen
      • 3- activates immune system
    • Scarlet fever - rash - erythrogenic toxin
    •  
    • non-suppurative
      • rheumatic fever
        • - inflammatory disease
        • - life threatening
        • - chronic sequalae
          • fever
          • heart
          • joints
            • rheumatic NOT rheumatoid arthritis
      Rheumatic fever is an inflammatory disease that occurs following a Group A streptococcal infection, (such as strep throat or scarlet fever). Believed to be caused by antibody cross-reactivity that can involve the heart, joints, skin, and brain, the illness typically develops two to three weeks after a streptococcal infection. Acute rheumatic fever commonly appears in children between the ages of 5 and 15, with only 20% of first-time attacks occurring in adults. The illness is so named because of its similarity in presentation to rheumatism.
    • Rheumatic fever -etiology
      • M protein
        • cross-reacts heart myosin
        • autoimmunity
      • Cell wall antigens
        • poorly digested in vivo
        • persist indefinitely
    • Rheumatic fever
      • Penicillin
        • terminates pharyngitis
        • decreases carditis
    • Acute glomerulonephritis immune complex disease of kidney
    • Major pathogenesis factors
      • lipoteichoic acid /F protein
        • fimbriae
        • binds to epithelial cells
      • M protein
        • anti-phagocytic
    • S. pyogenes fibronectin lipoteichoic acid/F-protein epithelial cells
    • M protein M protein fibrinogen peptidoglycan IgG Complement IMMUNE NON-IMMUNE r r r r r r
    • M protein
      • major target
        • natural immunity
      • strain variation
        • antigenicity
      • re-infection
        • occurs with different strain
    • Capsules
      • Anti-phagocytic
        • mucoid strains
    • Isolation and identification
      • β - hemolytic colonies
        • bacitracin inhibits growth
      • β - hemolytic colonies
        • group A antigen
      Bacitracin is a mixture of related cyclic polypeptides produced by organisms of the licheniformis group of Bacillus subtilis var Tracy, isolation of which was first reported in 1945. As a toxic and difficult-to-use antibiotic , bacitracin does not work well orally. However, it is very effective topically, and is a common ingredient of eye and skin antibiotic preparations. Its action is on gram-positive cell walls. It can cause contact dermititis due to allergic sensitivity to it.
    • Β - hemolysis
      • hemolysin O
        • sensitive oxygen
      • hemolysin S
        • insensitive oxygen
    • Modern Rapid “Strep” Test Throat swab extract (+/- streptococcal antigen) Antibody Liposome + - Streptococcal antigen
    • Post-infectious diagnosis (serology)
      • antibodies to streptolysin O
      • important if delayed clinical sequelae occur
    • Traditional serotyping of proteins: - M - T - R Typing Modern: - Sequencing of M protein gene
    • Group B streptococcus
      • neonatal meningitis
      • septicemia
      • transmission
        • vaginal flora
    • Group B streptococcus - identification
      •  hemolysis
      • hippurate hydrolysis
      • CAMP reaction
        • increases  hemolysis of S. aureus
    • Group D streptococcus
      • Growth on bile esculin agar
        • black precipitate
      • 6.5% saline
      • grow
        • enterococci
      • no growth
        • non-enterococci
    • Enterococci
      • distantly related to other streptococci
      • genus Enterococcus
      • gut flora
        • urinary tract infection
          • fecal contamination
        • opportunistic infections
          • particularly endocarditis
      • most common E. (S.) faecalis
    • Enterococci
      • resistant to many antibiotics
        • including vancomycin
          • terminal D-ala replaced by D-lactate
    • Minute colony streptococci
      • Various groups/hemolysis (e.g. group A)
        • genetically distinct
          • from large colony (e.g. S. pyogenes)
        • no rheumatic fever
      Large colony Minute colony
    • Viridans streptococci
      • diverse species
      • oral
      • dental caries
      •  hemolytic and negative for other tests
      • non-groupable.
      • includes S. mutans
        • endocarditis
        • tooth extraction