Module 2

• Causative Agent

  Any microbe capable of producing a disease
• Bacteria


  • Simple, one-celled microbes with double cell membranes that protect them from harm
  • Reproduce rapidly
  • Considered the most common cause of fatal infectious diseases
• Classification of Bacteria


  • Shape (cocci, bacilli, spirilla)
  • Need of oxygen (aerobic, anaerobic)
  • Response to staining (gram + or -, or acid fast)
  • Motility (motile; non-motile)
  • Tendency to capsulate (encapsulated, capsulated)
  • Capacity to form spores (spore forming, non-spore forming)
• Spirochete


  A bacterium with flexible, slender, undulating, spiral rods that possess cell wall
• Types of Spirochete

  • Treponema (Syphilis)
  • Leptospira (Leptospirosis)
  • Borrelia (Lyme Disease)
• Viruses

  • The smallest known microbes
  • Cannot replicate independently in the host's cells
  • Invade and stimulate the host's cells to participate in the formation of additional viruses
• Rickettsia


  Small, gram negative (-) bacteria-like microbes that can induce life threatening infections<|>Require a host cell for replication<|>Usually transmitted through the bite of arthropod carriers like lice, fleas, ticks, as well as through waste products
• Chlamydiae


  Smaller than rickettsia but larger than a virus<|>Common cause of infection of the urethra, bladder, fallopian tubes, and the prostate gland<|>Most common chlamydial infection is transmitted through sexual contact
• Fungi


  • Found almost everywhere on earth
  • Live in organic matter, soil, water, animals, and plants
  • Can live inside and outside the body
  • Beneficial in cheese, yogurt, beer, wine and certain drugs
• Protozoan


  Much larger than bacteria<|>Simplest single-celled organism of the animal kingdom<|>Parasitic Protozoa absorb nutrients from the body of the host
• Parasites


  Live on or within other organisms<|>Live at the expense of others and they don't usually kill their host but take only the nutrients they need
• Reservoir of Infection


  The environment and objects on which an organism survives and multiplies