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Skin > Agents of Bacterial Skin Infections: Staphlococci > Flashcards

Agents of Bacterial Skin Infections: Staphlococci Flashcards

1
Q

laboratory tests that distinguish Staphylococcus sp.

A
  • Colony Morphology on blood agar
    • Color and hemolysis
  • Gram stain: positive
  • Catalase: positive
  • Coagulase: positive in S. aureus
  • Coagulase negative:
    • Anaerobic: S. epidermidis
    • Aerobic: S. saprophyticus
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2
Q

Skin and Soft Tissue Infections caused by S. aureus

A
  • Furuncle
  • Carbuncle
  • Mastitis
  • Cellulitis
  • Impetigo
  • Wound infections
  • Invasive Infections
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3
Q

Furuncle

A
  • A boil is a skin infection involving an entire hair follicle and nearby skin tissue
  • begin as a tender, pinkish-red, swollen, firm area in the skin.
  • yellow or white point at the center is seen when the boil is ready to discharge pus.
  • Tx: heat and drainage
    • Antibiotics if invades subcutaneously
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4
Q

Hydradentis Suppurativa

A
  • Infection of the sweat gland
  • causes chronic scarring and pus formation of the underarms (axilla) and groin/inner thigh areas
  • Tx: antibiotics and corticosteroids
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5
Q

Folliculitis

A
  • Chronic furunculosis
  • can be stye near eye
  • Tx: topical mucopirocin to eliminate nasal colony
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6
Q

Staphylococcus Cellulitis

A
  • area which is red, hot, and tender

- Can be secondary infection from break in skin

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7
Q

Impetigo

A
  • Usually due to GAS, but 30% from staphylococci

- Same as seen in Strep

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8
Q

Ecthyma grangrenosum

A
  • wound infection
  • caused by Pseudomonas aeruginosa
  • environmental reservoir
  • round or oval lesion
  • Necrotic and less suppurative
  • A necrotic center is usually present with a surrounding erythematous edge
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9
Q

Vibrio vulnificus

A
  • wound infection
  • fluid filled blisters
  • from salt water exposure
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10
Q

MRSA

A
  • Methicillin resistant S. aureus

- skin infection seen in steroid injections and tattoos

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11
Q

S. aureus Virulence Factors: anti-phagocytic

A
  • Protein A: acts as an immunological disguise
  • Catalase: breaks down toxic H2O2 to H2O and O2
  • Leukocidin: pore forming toxin
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12
Q

S. aureus Virulence Factors: Riobotechoic & Techoic Acid

A
  • Bind Fibronectin

- Induces shock similar to endotoxin

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13
Q

S. aureus Virulence Factors: Coagulase

A
  • extracellular and surface bound

- Initiates conversion of fibrinogen to fibrin

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14
Q

S. aureus Virulence Factors: capsule

A
  • polysaccharide
  • max expression in vivo
  • 8 differnt serological types
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15
Q

S. aureus Virulence Factors: Hyaluronidase

A
  • Acts on Hyaluronic acid in CT

- Facilitates dissemination through subcutaneous tissues

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16
Q

S. aureus Virulence Factors: Cytotoxins (5)

A
  1. Alpha hemolysin: potent pore former; toxic to many cell types
  2. Beta toxin: sphingomyelinase C: kills cells via hydrolysis of membrane phospholipids
  3. Delta toxin: cytolytic for many cells; non-specfic detergent action
  4. Gamma toxin: pore forming toxin; lysis of neutrophils and macrophages
  5. Panton Valentine Leukocidin: pore forming toxin; lysis of neutrophils and macrophages
17
Q

Bullous Impetigo

A
  • appear around the diaper region, axilla, or neck
  • exfoliative toxins cause for the epidermis and dermis to separate
  • Exfoliating toxins are serine proteases that specifically bind to and cleave desmoglein 1
18
Q

Scalded skin syndrome

A
  • Localized bullous impetigo
  • widespread formation of fluid filled blisters that are thin walled and easily ruptured
  • positive for Nikolsky’s sign: slight rubbing of the skin results in exfoliation
  • Exfoliatins (serine proteases) cause splitting of desmosomes in the stratum granulosum
19
Q

Toxic Shock Syndrome

A
  • Caused by toxic shock syndrome toxin-1
  • Sudden onset fever chills, vomiting, diarrhea, muscle pains and rash
  • Later: hypotension, mucus membrane involvement, multiple system failure, desqumation
  • Risk: menstruating women and women w/ barrier contraceptive devices, and nasal surgery
20
Q

S. aureus Resistance to Penicillin & Methicillin

A
  • Penicillinase producing S. aureus
    • plasmid encoded
    • transfer by conjugation or transduction
  • Methicillin: semi-synthetic penicillin
    • resistant to penicillinase
    • Developed resistance due to mecA gene
21
Q

S. aureus Vancomycin Resistance

A
  • Due to acquisition of vanA gene

- Peptidoglycan precursor contains D-ala-D-lactate rather than D-ala-D-ala

22
Q

S. epidermidis

A
  • UTIs
  • Osteomyelitis
  • Endocarditis
  • Bacteremia
  • Endophthalmitis
  • Infections of indwelling devices (catheters, pacemakers, etc)
    • Biofilm causes irreversble adherence that protects against antibiotics
23
Q

S. intermedius

A
  • Coagulase positive
  • Invasive zoonotic pathogen
    • dog bites

Skin (6 decks)

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