Quiz (Ch. 37)
Quiz (Ch. 38)

Selected bacterial diseases

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Last revised: Monday, April 24, 2000
Ch. 37, 38 in Prescott et al, Microbiology, 4th Ed.
Note: These notes are provided as a guide to topics the instructor hopes to cover during lecture. Actual coverage will always differ somewhat from what is printed here. These notes are not a substitute for the actual lecture!
Copyright 2000. Thomas M. Terry
Bacterial Disease Case Study: Staph infections
  • Staphylococcus aureus is so common that it is hard to appreciate the full range of its virulence.
  • S. aureus is an opportunist, a common member of normal flora that rarely afflicts healthy individuals, but can seize on sudden opportunity (such as a break in the skin, a burn, or a superabsorbent tampon) to turn vicious, activating an extraordinary range of virulence factors. Over all of human history, S. aureus may be responsible for more collective suffering and pain than any other single bacterium!

  • S. aureus infections are especially common in hospitals. About 1/3 of strains isolated from hospitalized infections are now resistant to all antibiotics except vancomycin, and resistant strains to that drug are beginning to show up!
  • Diseases caused by S. aureus include:
    1. boils and abcesses
    2. cellulitis
    3. furuncles and carbuncles
    4. impetigo and "scaled skin" syndrome
    5. pneumonia, endocarditis, and septicemia
    6. toxic shock syndrome:
      • many strains of Staph. aureus release "superantigens", act asactivators of T-cells.
      • Normally, a foreign antigen might cause 0.001% of T-cell population to divide; superantigen can cause 2-20% to divide.
      • Result = upset delicate balance that normally keeps T-cell response very local and specific; instead, many T-cells are killed, much energy is wasted in ways that don't harm pathogen. Responsible for "Toxic shock syndrome".
  • S. aureus carries a number of virulence factors, including:
    1. an exotoxin that causes skin layers to separate and slough off (scalded skin syndrome)
    2. an enterotoxin that causes vomiting and diarrhea
    3. an exotoxin that causes toxic shock syndrome, leading to death
    4. the enzyme coagulase, that coagulates blood and prevents phagocytes from reaching the site of infection
    5. enzymes called leukocidins that kill phagocytes, resulting in pus
    6. and many more .....
  • Recently, scientists have begun to understand how virulence factors in S. aureus are regulated. RAP (RNAIII activating protein) controls production of toxins and other virulence proteins. Naomi Balaban discovered RAP a few years ago, and suggested that this protein shifts S. aureus from early stage of infection (attachment) into its later stage of infection (virulence), turning on toxins and other enzymes.
  • If animals could be immunized against RAP, might be possible to "short-circuit" the expression of Staph virulence factors. A report in the journal Science, 280:438-440 (1998) published April 17, 1998 suggests this possibility.

Entry of Pathogens into hosts

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