Controling Microbial Growth in Vitro

• In vitro


  Events that occur outside the body
• In vivo


  Events that occur inside the body
• Growth


  Orderly increase in the sum of all components of an organism, entailing replication of all cellular structures, organelles and components
• Microbial Growth


  Increase in the number of cells, not an increase in the size of the organism

  
• Bacterial Growth


  Proliferation or multiplication of bacteria
• Nutritional Requirements


  • Carbon- makes up the structural backbone of all organic molecules. (autotrophs/lithotrophs and heterotrophs/organotrophs)
  • Nitrogen, sulfur and phosphorus
  • Inorganic ions
  • Growth factors
• Autotrophs/Lithotrophs


  Microorganisms that utilize inorganic compounds, salts and water as their sole source of carbon
• Photolithotrophs


  Microorganisms that derive their energy from light
• Chemolithotrophs


  Microorganisms that derive their energy from the oxidation of inorganic substances
• Heterotrophs/Organotrophs


  Microorganisms that utilize organic substances like sugars or glucose as their carbon source
• Photoorganotrophs


  Source of energy is light
• Chemoorganotrophs


  Source of energy is oxidation of organic substances
• Magnesium


  • Stabilizes ribosomes, cell membranes and nucleic acids, serves as a co-factor for many enzymes
• Potassium


  • For the normal functioning and integrity of ribosomes and also for certain enzymatic activities
• Calcium


  • Important constituent of the cell walls of Gram-positive bacteria, contributes to the resistance of bacterial endospores against adverse environmental conditions
• Iron


  • Part of cytochrome and functions as co-factor in enzymatic activities
• Trace elements


  Components of enzymes and function as co-factors, necessary for the maintenance of protein structure
• Growth factors


  Include vitamin B complex, amino acids, purines and pyrimidines
• Physical Requirements


  • Moisture or water
  • Oxygen
  • Temperature
  • pH
  • Barometric pressure
  • Osmotic pressure and salinity
• Aerobes


  Utilize molecular oxygen for energy
• Strict aerobes


  Strictly require oxygen for growth
• Obligate/Strict anaerobes


  Cannot survive in the presence of oxygen, lack enzymes like superoxide dismutase and catalase
• Aerotolerant anaerobes


  Can resist exposure to oxygen and are not killed by its presence
• Microaerophilic anaerobes


  Able to grow at low oxygen tension but rate of growth is diminished
• Facultative organisms


  Can grow under both aerobic or anaerobic conditions
• Thermophiles


  Heat loving, grow best at an optimum temperature range of 50 - 60°C
• Hyperthermophiles (extreme thermophiles)


  Favor temperatures above 100°C
• Mesophiles


  Require an optimum temperature of 20 - 40°C
• Psychrophiles


  Require an optimum temperature of 10 - 20°C, love cold temperature and thrive in cold ocean water
• Psychroduric organisms


  Able to endure very cold temperature and can be preserved in the frozen state
• Microorganisms classified by pH

  • Alkalophiles (pH 8.4 – 9.0)
  • Neutrophiles (pH 7.5 – 8.0)
  • Acidophiles (pH 6.5 – 7.0)
• Piezophiles


  Thrive deep in the ocean and in oil wells, where the atmospheric pressure is very high
• Halophiles


  Require high salt concentration for growth
• Osmophiles


  Require high osmotic pressure
• Haloduric organisms


  Do not prefer to live in salty environments but are capable of surviving there
• Phases of Bacterial Growth Curve


  • Lag phase- prepare for cell division, do metabolic process
  • Logarithmic/Exponential/Log phase- grows in number, determines generation time
  • Stationary phase- equilibrium (sporulation)
  • Death phase or decline phase-more are dying (sporulation still exist)

  
• Lag phase


  Bacteria absorb nutrients, synthesize enzymes, and prepare for cell division. No increase in number but increase in size.

  
• Logarithmic/Exponential/Log phase


  Rapid cell division, resulting in increase in the number of bacteria. Cells are metabolically active. Generation time can be determined.
• Stationary phase


  Rate of growth slows down, nutrients are depleted and toxic wastes accumulate. Some bacterial cells may die but number of living cells equals number of dead cells. Sporulation occurs.

  
• Death phase or decline phase


  Rapid cell death, number of dead cells greater than number of living cells due to depletion of nutrients and accumulation of waste. Sporulation continues.