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What are the common normal flora of the skin?
- Corynebacterium (dipheroids)
- Coagulase negative staphyococci
- Proprionibacterium acnes
Infections of the epidermis in areas in and around hair include what?
What are the common bacterial pathogens found in areas in and around hair?
- Staphylococcus aureus
- Pseudomonas aeruginosa
Infections of the dermis include what?
What is the common bacterial pathogen associated with infections of the dermis?
Infections of subcutaneous fat and tissue include what?
What are the common bacterial pathogens associated with infections of subcutaneous fat and tissue?
- Staphylcoccus aureus
Infections of muscle and fascia include what?
- Necrotizing fasciitis
What are the common bacterial pathogens associated with infections of muscle/fascia?
- Streptococcus pyogenes
- Staphylcoccus aureus
- Anaerobes (esp Clostridium)
What is the role of the capsule found in S. aureus?
Antiphagocytic, Prevents complement from binding to its receptor on a phagocyte
What is the role of the slime layer found in S. aureus?
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)
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
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
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)
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
What was the basis for Vancomycin resistant S. aureus?
Plasmid-mediated transfer of the vanA gene from enterococci with vancomycin resistance via a transposon
What illnesses are associated with S. aureus infections? (3)
- Scalded skin syndrome
- Food poisoning
- Toxic shock syndrome
How is S. aureus diagnosed via a culture?
- Blood agar: yellow color, beta hemolytic
- Catalase positive
- Coagulase positive
Pseudomonas aeruinosa- gram and shape?
Long thin gram negative bacilli
Which adhesins are associated with Pseudomonas aeruginosa?
pili, flagella, LPS
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
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
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)
What factors contribute to antibiotic resistance of P. aeruginosa?
- -Efflux pumps
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)
Which skin infections are associated with P aeruginosa?
Bacillus anthracis- gram and shape?
- Gram positive bacillus, large with flattened ends
- Spore former
What is the role of the capsule found in B. anthracis?
- -Mediates initial invasion
- -Poly-D-glutamyl capsule
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
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
Which parts of the body are anaerobes the predominant normal flora?
- Oral cavity
- Genitourinary tract
- GI tract
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