Chap 7

• Enriched media


  Supports the growth of nutritionally demanding bacteria
• Enrichment media


  Prevents the growth of undesired or contaminated microorganisms
• The father of bacteriology is Antonie van Leuwenhoek
• Joseph Lister is the father of modern surgery/antiseptic surgery
• Louis Pasteur is the father of modern microbiology
• Koch's Postulates


  1. Recognizing the presence of an agent in all cases of disease

  2. Isolating that organism

  3. Re-introducing the organism causes similar symptoms

  4. The organism can be isolated again

  
• Koch's postulates were limited: viral pathogens were not culturable in early microbiology labs and asymptomatic carriers break this protocol

  
• Some pathogens do not exhibit the same presentation in mice (no animal model of infection with that particular bacteria)

  
• Mycobacterium leprae cannot be 'grown in pure culture' in the lab
• Harmless bacteria can cause disease if

  • It has acquired extra virulence factors making it pathogenic
  • It gains access to deep tissues via trauma, surgery, an IV line, etc
  • It infects an immunocompromised patient
• Use of the following in the selective cultivation of microorganisms

  • Chemicals
  • Dyes
  • Antimicrobial agents
  • pH
  • Temperature of incubation
  • Atmospheric conditions
• Selective culture medium


  Used to isolate a particular bacterial species or genus by adding inhibitors to eliminate unwanted microbial flora
• Bacteriophage (phage)


  A virus that infects and replicates within bacteria and archaea
• Antibiotics more commonly used as selective agents in culture media

  • Molecules that target Gram-positive bacteria (penicillin G, bacitracin, vancomycin)
  • Molecules that target Gram-negative bacteria (colistin, polymyxin B)
  • Molecules that target yeast and fungi (Amphotericin B, cycloheximide, nystatin)
• Antiseptics


  Kill microorganisms on your skin (washes, rubs, and antiseptic wipes)
• Disinfectants


  Used to kill germs on non-living surfaces
• Disinfection


  The act of disinfecting something by using disinfectant to destroy, inactivate or reduce the concentration of pathogenic agents
• Chemical substances used to inhibit certain bacteria

  • Potassium tellurite and bile salt inhibit Gram-positive bacteria
  • Lithium chloride inhibits Gram-negative bacteria
• Dyes used as a colour indicator in a culture medium or as a selective agent against certain bacteria

  • Crystal violet (CV) inhibits the growth of Gram-positive bacteria by inducing DNA lesions
  • Malachite green inhibits Gram-positive and -negative bacteria
  • Methylene blue inhibits Gram-positive bacteria and some yeast by making use of toxic dyes
• Sodium salts


  Used to select halophilic (salt-loving) bacteria that resist very high amounts of salts