1-3

• Learning Outcomes


  • Be able to describe how environmental influences, including temperature, pH, osmolality, oxygen and pressure affect bacterial growth
  • Be able to define antimicrobial control measures including sterilization, disinfection, antiseptics and sanitation
  • Be able to describe the process of autoclaving
• Oxygen requirements


  • Aerobic
  • Anaerobic
  • Obligate aerobe
  • Obligate anaerobe
  • Facultative anaerobe
  • Microaerophile
  • Aerotolerant anaerobe
• Oxygen effect


  • Growth
  • No growth
  • Required
  • Toxic
  • Used if available
  • Required at lower concentration
  • Tolerates but not required
• Effects of temperature on microbial growth

  • High temperatures: Proteins denature (inc enzymes), Membranes become too fluid
  • Low temperatures: Membranes become too rigid and fragile
• Effects of temperature on microbial growth

  1. Growth rate

  2. Optimum

  3. Maximum

  4. Minimum
• Chemotaxis


  Movement of a bacterium in response to chemical gradients
• Extreme environments


  1. Growth rate

  2. Temperature (°C)

  3. Psychrophiles (<15°C)

  4. Mesophiles (20 - 40 °C)

  5. Hyperthermophiles [extremophiles] (>45°C)
• pH


  • Measure of H+ ions in solution
  • More H+ ions the more acidic
  • Logarithmic scale
  • Microorganisms are sensitive to pH
  • H+ ions affect hydrogen bonds
• Most bacteria grow between pH 6-8
• Acidophiles


  Prefer acidic conditions
• Alkalinophiles


  Prefer alkaline conditions
• Water


  • Main component of cells (~70%)
  • Dissolve nutrients
  • Component of many metabolic reactions
  • Osmosis: Water diffuses across a semi-permeable membrane
• Movement of water


  1. From low concentration to high concentration

  2. Hypertonic solution: High concentration of solutes, Cell loses water, Shrivel

  3. Hypotonic solution: Low concentration of solutes, Cell takes up water, Expand
• Natural ecosystems are typically low in nutrients (oligotrophic), but diversity means numerous species compete for the same limiting nutrients
• Maximum diversity in an ecosystem is partially maintained by different nutrient-gathering profiles of competing microbes
• Antimicrobial control methods


  • Sterilization: Destroying all living cells, spores, and viruses
  • Disinfection: Killing or removing disease-producing organisms from inanimate surfaces
  • Antiseptics: Removing pathogens from the surface of living tissues
  • Sanitation: Reducing the microbial population to safe levels, involving both cleaning and disinfecting
• Sterilization


  Autoclave
• Autoclave


  • Machine that is used to remove any trace of microorganisms from abiotic surfaces
  • Uses high temperature and pressure
  • Moist heat better due to the ability of water to penetrate cells
  • At high pressure the boiling point of water rises to a temperature bacteria at sea level are not exposed to – hence it kills them