Lecture 19: Microbial Infections of the Skin

Introduction

• Topic: Microbial infections of the skin
• Focus: Microorganisms such as Propionibacterium acnes, Staphylococcus aureus, and Streptococcus pyogenes

Acne and Skin Anatomy

• Acne
  • Caused by Propionibacterium acnes
  • Common in teenagers due to hormonal changes
  • Results in pus-filled pimples
• Skin as a Barrier
  • Outer layers are dead, replaced monthly
  • Covered in salt, which inhibits microorganism growth
  • Passageways exist allowing microorganism entry (hair follicles, sweat pores)

Terminology of Skin Infections

1. Vesicle: Small fluid-filled lesion (like a blister)
2. Abscess: Localized pus surrounded by inflamed tissue (boil/hair follicle infection)
3. Pustule: Raised pus-filled lesion
4. Cellulitis: Inflammation and infection of skin, serious
5. Myositis: Inflammation of skeletal muscles
6. Necrotizing Fasciitis: "Flesh-eating bacteria," causes tissue destruction

Hair Follicle Infections

• Caused by: Staphylococcus aureus
• Types:
  • Folliculitis: Small red bumps (pimples)
  • Furuncle (Boil): Larger, painful, pus-filled
  • Carbuncle: Larger area with multiple drainage points
• Pathogenesis:
  • Bacteria attaches to hair follicle, moves to sweat glands
  • Causes inflammation and accumulation of white blood cells (pus)
• Epidemiology & Treatment:
  • Spread through contact or fomites
  • Antibiotics and wound care, including debridement

Staphylococcus aureus Infections

• Scalded Skin Syndrome
  • Begins at mouth, spreads rapidly
  • Symptoms: Reddened skin, peeling
  • Caused by an a/b toxin
  • Common in children, especially newborns
• Staphylococcal Wound Infection
  • Caused by S. aureus entering through wounds
  • Coagulase and Protein A as virulence factors
  • Prevention through cleanliness

Streptococcus pyogenes Infections

• Impetigo
  • Affects infants/children
  • Symptoms: Red sores, yellow-brown crusts
  • Spread by contact, treatment with antibiotics
• Necrotizing Fasciitis
  • Rare, enters through skin breaks
  • Produces exotoxin A, leading to rapid tissue damage
  • High mortality rate, treatment with surgery and penicillin
• Virulence Factors:
  • Many factors similar to S. aureus
  • Includes enzymes like hyaluronidase and toxins

Conclusion

• Covered various types of skin infections caused by microorganisms
• Next Lecture: More skin infections

These notes summarize the key points and important details about skin infections caused by microorganisms, focusing on the causative agents, symptoms, pathogenesis, and treatment options.