Lecture 03 - Staphylococcus and Streptococcus

Lecture 03 - Staphylococcus and Streptococcus - it breaks...

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Lecture 03 - Gram Positive Cocci: Staphylococcus and Streptococcus. Outline: GRAM POSITIVE! Staphylococci Staphylococcus aureus Coagulase-negative staphylococci Beta-hemolytic streptococci Group A strep ( S. pyogenes ) Group B strep ( S. agalactiae ) Alpha-hemolytic streptococci Viridans strep, S. bovis, Enterococci M I-15a. Describe the properties and classification of the genus Staphylococcus , including its major human pathogens, S. aureus, S. epidermidis and S. saprophyticus Staphylococcus - Gram (+) & cocci (round) - “Staphylos” = Grapes (clusters of grapes) pairs, tetrads - nonmotile - non-spore forming - Cell wall (features of the gram(+) bacteria (NAM and NAG) - Catalase o if present – resistance to oxidative burst o Critical in staph and easy to detect presence test and see if it will break down peroxides to water and oxygen o helps the organism counter the toxic compound from the host’s WBC - Coagulase o produce through surface form or free form (and can be pick up with liquid assay test this with the coagulase test (inoculate rabbit serum) it breaks down the fibrinogen triggering the clotting cascade a positive test is when there are precipitate (which means S. aureus ) o it will also help the organism coat itself with fibrin providing protection from the host’s immune response and makes it difficult for opsonize o Positive: S. aureus – major human pathogen o Negative: S. epidermitidis and S. saprophyticus – low virulence; nosocomial infections Coagulas e Agar Plate Color S. aureus + Yellow (Aureus = golden) S. epidermitidis - White S. saprophyticus - White Staphylococcus Epidermidis - Present as commensal on skin of nearly 100% of people - Common contaminant in bacterial cultures - Pathogen for patients with indwelling catheters o Biofilm formation and release of exopolysaccharide “slime” o virulence = biofilm - less virulence more resistant Staphylococcus Saprophyticus - UTIs in women and elderly men M I-15b. List three important virulence (abilities of an infection to produce disease) factors of S. aureus and describe how they contribute to pathogenesis
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Virulence properties here: - Adhesive factors o Clumping factor (adherence to fibrinogen and fibrin) - Catalase - Hemolysin factors - these properties turn on and off depending on the signals and environmental factors - 1. Attachment to cells via extracellular matrix proteins o INVASION of the host then evasion of the host response - 2. Evade host immune defense mechanisms (e.g. PMNs, complement) o a lot easier when pt is immune-compromise b/c the weaken immune system (you will favor the infectious process) o ie. diabetics kill organism is no effective anymore encounter mostly common - 3. Toxin production facilitates spread and produces host tissue injury MI-15d. Describe the clinical manifestations of local and systemic S. aureus infection Staphylococcus aureus - Normal healthy people = 30% carriers, small % go on to
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Lecture 03 - Staphylococcus and Streptococcus - it breaks...

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