Important Note

Tufts ended funding for its Open Courseware initiative in 2014. We are now planning to retire this site on June 30, 2018. Content will be available for Tufts contributors after that date. If you have any questions about this please write to

Tufts OpenCourseware
Author: Amelia Virostko

1. Introduction

  1. Most common pyogenic bacteria
  2. Can cause abscesses, food poisoning, urinary tract infections (UTIs), toxic shock and scalded skin, osteomyelitis, and endocarditis
  3. Resistant to heat, dessication, and high salt concentrations
  4. S. epidermidis found on skin of most people, but not usually pathogenic
  5. S. aureus primarily responsible for infections

2. Identification

  1. Gram-positive cocci

3. Encounter

  1. S. aureus found in 30% normal individuals
  2. Spread through hand contact and aerosols

4. Entry

  1. Compromise in immunity or bacterial overload necessary for pathogenesis

5. Spread/Multiplication

  1. Usually localized infection

6. Damage

  1. S. aureus can produce numerous syndromes
    1. Abscess or boil formation can lead to cellulitis or impetigo
    2. If bone is affected produces osteomyelitis affecting heart and brain
    3. Scalded Skin Syndrome (SSS) life-threatening
    4. Toxic Shock Syndrome (TSS) produces fever, rash, and hypotension
  2. S. epidermidis can cause endocarditis in prosthetic heart valve or septicemia in indwelling medical device
  3. S. saprophyticus responsible for UTIs

7. Virulence Factors

  1. S. aureus
    1. Capsule: anti-phagocytic if present
    2. Peptidoglycan: activates alternative complement pathway
    3. Teichoic acid: complement activation and pro-inflammatory
    4. Protein A: inhibits IgG
    5. Catalase: prevents neutrophils from killing bacteria
    6. Coagulase: promotes clot formation inhibiting WBC activity
    7. Staphylokinase: activates plasminogen
    8. Alpha toxin: creates channels in cell membranes causing hemolysis
    9. Hyaluronidase: hydrolyzes connective tissue and facilitates spread
    10. Virulence enhancers: lipases, proteases, DNases
  2. S. epidermidis
    1. Exopolysaccharide slime layer: sticks to surfaces
    2. Fimbriae: help bacteria stick to surfaces

8. Diagnosis

  1. Resemble grape clusters on Gram stain
  2. S. aureus produces golden colonies and is coagulase-positive
  3. Catalase-positive
  4. S. saprohyticus is Novobicin-resistant

9. Treatment

  1. Drain abscesses to prevent spread
  2. Many staphylococci resistant to penicillins, semisynthetic penicillins, and cephalo- sporins
  3. Treat with vancomycin or gentamycin

10. Outcome

  1. Can produce a wide variety of symptoms differing in severity