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What are the common normal flora of the skin?
- Corynebacterium (dipheroids)
- Coagulase negative staphyococci
- Proprionibacterium acnes
- Candida
- Streptococcus
- Micrococcus
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Infections of the epidermis in areas in and around hair include what?
- Folliculitis
- Furuncles
- Carbuncles
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What are the common bacterial pathogens found in areas in and around hair?
- Staphylococcus aureus
- Pseudomonas aeruginosa
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Infections of the dermis include what?
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What is the common bacterial pathogen associated with infections of the dermis?
Bacillus anthracis
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Infections of subcutaneous fat and tissue include what?
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What are the common bacterial pathogens associated with infections of subcutaneous fat and tissue?
- Staphylcoccus aureus
- Anaerobes
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Infections of muscle and fascia include what?
- Necrotizing fasciitis
- Gangrene
- Myositis
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What are the common bacterial pathogens associated with infections of muscle/fascia?
- Streptococcus pyogenes
- Staphylcoccus aureus
- Anaerobes (esp Clostridium)
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What is the role of the capsule found in S. aureus?
Antiphagocytic, Prevents complement from binding to its receptor on a phagocyte
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What is the role of the slime layer found in S. aureus?
Biofilm formation
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What comprises the adhesins found in S. aureus?
- MSCRAMMs :
- Coagulase (binds to and activates prothrombin)
- Collagen binding protein (binds collagen)
- Clumping factor (binds fibrinogen)
- Fibronectin-binding protein (binds fibronectin)
- Protein A (binds the Fc portion of IgG)
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What does coagulase do and what are the two types? (S. aureus)
- -Converts soluble fibrinogen in plasma to insoluble matrix fibrin
- -Bound coagulase (on the surface of the bacteria, causes the bacteria to clump together); the more bacteria in a given location, the more effective they are in shielding each other from an immune response and excreting toxic factors in high quantities
- -Free coagulase (secreted from bacteria into the environment) causes a protective fibrin clot to form around bacteria
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What toxins are associated with S. aureus?
- Exfoliative toxin- proteases that split the intracellular bridges in the stratum granulosum of the epidermis
- Exotoxins- Superantigens, non-specifically activate T cells. Ex) TSST, enterotoxin, cytotoxins
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Which enzymes are associated with the virulence factors of S. aureus?
- Protease- destroys host cell matrix
- Hyaluronidase- destroys host cell matri by hydrolyzing hyaluronic acid
- Leukocidin- kills leukocytes
- Lipases- hydolyzes lipids
- Nucleases- hydrolyzes DNA
- (also teichoic acid and lipoteichoic acid- bind fibronectin)
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What was the basis for the development of MRSA?
- -Acquisition of the mecA gene that encodes a mutant penicillin binding protein (PBP2A)
- -PBP2A has low affinity for beta lactams and can substitute for the enzymatic activity of PBPs and allow complete of cell wall assembly
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What was the basis for Vancomycin resistant S. aureus?
Plasmid-mediated transfer of the vanA gene from enterococci with vancomycin resistance via a transposon
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What illnesses are associated with S. aureus infections? (3)
- Scalded skin syndrome
- Food poisoning
- Toxic shock syndrome
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How is S. aureus diagnosed via a culture?
- Blood agar: yellow color, beta hemolytic
- Catalase positive
- Coagulase positive
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Pseudomonas aeruinosa- gram and shape?
Long thin gram negative bacilli
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Which adhesins are associated with Pseudomonas aeruginosa?
pili, flagella, LPS
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What is the role of alginate? (virulence factor found in P. aeruginosa)
- -Polymer of mannuronic and guluronic acid
- -Forms a viscous gel around the organism
- -Strains that produce alginate are mucoid
- -Plays a role in biofilm formation
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What is the role of Exotoxin A in P. aeruginosa?
- -Disrupts eukaryotic cell protein synthesis by blocking peptide chain elongation
- -ADP ribosylates EF2, stops host cell protein synthesis
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Which enzymes are associated with virulence in P. aeruginosa?
- -Proteases- tissue damage
- -Pigments- pyocyanin (catalyzes production of superoxide and H2O2 and stimulates IL-8), pyoverdin (siderophore, binds iron)
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What factors contribute to antibiotic resistance of P. aeruginosa?
- -Efflux pumps
- -Beta-lactamase
- -Porins
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What are the defining features of P. aeruginosa in culture? (diagnostic characteristics)
- Oxidase positive
- Grows on MAC and BAP
- Lactose negative
- Metallic sheen
- Mucoid colonies
- Produces pigments
- Grapelike or corn taco like odor (ew)
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Which skin infections are associated with P aeruginosa?
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Bacillus anthracis- gram and shape?
- Gram positive bacillus, large with flattened ends
- Spore former
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What is the role of the capsule found in B. anthracis?
- -Mediates initial invasion
- -Poly-D-glutamyl capsule
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What are the three components of the Anthrax toxin?
- 1) Protective agent- binds to host cell receptor
- 2) Edema factor- cyclase (increases cAMP) causing edema
- 3) Lethal factor- protease (cleaves MAPK) leading to cell death
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What is the clinical manifestations of Cutaneous anthrax?
Spores enter the skin and a papule develops. The papule ulcerates and eventually forms a black eschar
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Which parts of the body are anaerobes the predominant normal flora?
- Oral cavity
- Genitourinary tract
- GI tract
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What are the clues to an anaerobic infection?
- -Infection adjacent to surfaces that normally harbor anaerobes as normal flora
- -Putrid odor
- -Abscess formation
- -Presence of gangrenous tissue necrosis
- -Gas formation
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