Infection of Skin and Soft Tissue

Question 1

Staphylococcus aureus causes what 4 skin infections?

Answer 1

1. Folliculities
2. Furuncles
3. Toxic shock syndrome
4. Bacteremia

Question 2

Streptococcus pyogenes causes which six skin infections?

Answer 2

1. Cellulitis
2. Lymphangitis
3. Impetigo
4. Erysipelas
5. Necrotizing fasciitis
6. Toxic shock syndrome

Question 3

Which enzymes affect spread and multiplication in skin infections?

Answer 3

• Hyaluronidase (spreading factor, Staph and Strep use as toxin)
• Hemolysins (destroys RBC)
• Lipases
• Collagenase
• Elastases

Question 4

What are predisposing risk factors to exogenous skin infections from staph or strep?

Answer 4

• Excessive moisture
• Trauma
• Introduction of foreign body
• Pressure
• Compromised blood supply

Question 5

What is the skin response to exogenous infections? (3)

Answer 5

1. spreading infections :
   
   • impetigo- epidermis
   • Erysipelas- dermal lymphatics
   • Cellulitis- subcutaneous fat layer
2. abscess formation:
   
   • folliculitis, furuncles/boils
   • carbuncles
3. necrotizing infection
   
   • Fasciitis and gas gangrene/myonecrosis

Question 6

What organism causes gas gangrene?

Answer 6

Clostridia

Question 7

Of staphylococci and streptococci which is catalase +?

Answer 7

Staphylococci

Question 8

Which Staphylococci is coagulase (+) and (-)?

Answer 8

• (+): S. aureus
• (-):
  
  • S. epidermidis (novobiacin sensitive)
  • S saprophyticus (novobiacin resistant)

Question 9

• Folliculitis is caused by which bacteria?
• What does it cause?

Answer 9

• Staphyloccocus aureus
  
  • infects sebaceous glands and hair follicles become inflamed
  • There is an influx of neutrophils
  • fibrin is deposited (site walled off) and an abscess is made

Question 10

Furuncles/ Carbuncles are abscess is? Caused by what bacteria?

Answer 10

• S. aureus
  
  • Abscess in subcutaneous tissue
    
    • Furuncle= single
    • Carbuncle= Multiple, interconnected

Question 11

Necrotizing fasciitis, myonecrosis and Gangarene are rapidly progressing? What toxin is produced/ which bacteria?

Answer 11

• Rapidly progressing cellulitis
  
  • extensive necrosis of subcutaneous tissue (acute)
• Toxin producing Clostridium perfringens and S. pyogenes produce virulence factors (particularly M protein)

Question 12

Symptoms of Necrotizing Fasciitis?

Answer 12

Intense pain, fever inflammation

Question 13

• What kind of bacteria is Clostridium perfringens?
• What toxins does it produce?

Answer 13

• Gram positive bacilli (anaerobic)
  
  • spore forming
• Toxins A-E
  
  • Exotoxins: alpha toxin hydrolyzes cell membranes
  • Phospholipase
  • Hemolysins (destroy RBC)
  • Collagenases

Question 14

What are 3 cutaneous responses to bacterial toxins?

Answer 14

• Toxic shock syndrome
• Scalded fever syndrome
• Scarlet fever

Question 15

Toxic shock syndrome is caused by which bacteria? MOA?

Answer 15

• Staphylococcus aureus producing toxins
• Binds to MHC and TCR outside of antigen binding site
  
  • cause overwhelming release of IL-1,IL-2, INF gamma and TNF alpha
  • —> shock

Question 16

Symptoms of Toxic Shock syndrome?

Answer 16

• Multisystem involvement: shock, fever, rash
• desquamation (skin peeling)
• septicemia (infection in blood)
• toxemia

Question 17

• Scalded Skin Syndrome is caused by which bacteria?
• MOA?
• Characterized by?

Answer 17

• Staph. aureus
  
  • exfoliation toxin producing (Exotoxin)
  • exotoxin destroys keratinocyte attachments in stratum granulosum (separation of top layer of epidermis)
• Characterized by:
  
  • fever
  • generalized erythematous rash with sloughing of upper layers of epidermis

Question 18

• Ecthyma gangrenosum causes necrotic skin lesions
  
  • caused by which type of bacteria?
  • Typically seen in which patients?
  • Toxins produced?

Answer 18

Pseudomonas aeruginosae;

• gram (-) rod that is oxidase positive
  
  • Opportunist pathogen
    
    • ​typically seen in immune compromised patients
  • Major nosocomial (in hospital) pathogen has multi drug resistance

Toxins:

• Endotoxin
• Exotoxin A (inhibitor of EF in eukaryotic protein synthesis)
• Extracellular slime Pigments

Question 19

Mycobacteria are what kind of bacteria?

Answer 19

• Gram (+) cell wall
• Acid fast (mycolic acid)
• slow growing

Question 20

• Mycobacterium terberculosis
• M. marinum
• M. ulcerans

All cause?

Answer 20

• All cause chronic ulcers
  
  • ​M. terberculosis= TB
  • M. Marinum= swimming pool
  • M. Ulcerans= in tropical countries

Question 21

Nocardia brasiliensis which is a bacteria that causes chronic ulcers is what kind of bacteria?

Answer 21

• Branching and intracellular opportunist
• Partial acid fast
• Beaded gram (+) bacilli

Question 22

Main virulence factosr of Staph. aureus and Strep. pyogenes?

Answer 22

• Strep. pyogenes:
  
  • M protein
  • exotoxins
  • streptolysins S&O
  • Streptokinas A&B
  • hyaluronidase
• Staph. aureus:
  
  • Proteins A
  • Capsule
  • Coagulase
  • Mucopeptide

Question 23

• Where is the location of beta lactamases in bacteria?
• How are they resistance to antibiotics like penicillin?

Answer 23

• Beta lactamases are excreted into extracellular space by Gram (+) bacteria and into periplasmic space by gram (-) bacteria
• beta lactamase enzyme cleaves beta lactam ring rendering antibiotic ineffective

Question 24

• Subcutaneous tissue connects?
• Composed of?

Answer 24

• Connects dermis to the deeper fascia
• has fascial layers (Scarpa’s and Camper’s)
• Composed of:
  
  • loose connective tissue
  • stored fat (thickness varies greatly)
• Contains
  
  • vessels
  • nerves
  • glands

Question 25

Function of subcutaneous tissue?

Answer 25

• thermoregulation (insulation)
• provides padding for bony prominences

Question 26

What are two examples of excessive formation of collagen during tissue repair?

Answer 26

1. Hypertrophic scar (raised scar); does NOT extend beyond boundaries of original wound
   
   • Thermal or traumatic injury involving deep dermis
2. Keloid (genetic; African Americans)
   
   • Scar grows beyond boundary of wound