microbio

• Physical requirements for microbial growth

  • Temperatures
  • pH
  • Osmotic Pressure
• Psychrophiles/Psychrophilic


  • Cold-loving microorganisms specifically bacteria and archaeans
  • Can grow at 0°C
  • Optimum growth temp: 15°C (24° maximum)
  • Cannot grow anymore at 25°C
  • Found in polar regions (Arctic and Antarctic regions) and freezer
  • Prefers lower temperature than Psychrotrophs
• Psychrotrophs


  • Cold-loving microbes
  • Can live at temp 0°C
  • One of the spoilage-causing microorganisms
  • Optimum temp: between 20°C - 30°C (39°C maximum)
  • Cannot grow anymore at 40°C
  • Can be found inside the refrigerators
• Mesophiles/Mesophilic Bacteria


  • Moderate-temperature-loving microbes
  • Include most of the common spoilage and disease organisms
  • Most common type of microbe
  • Medically important microbes
  • We carry mesophiles that can be pathogenic
  • Found inside the body, on the skin, surface of the body
  • Minimum growth temp: 10°C
  • Maximum GT : 50 °C
  • Optimum GT : 25°C - 40°C
• Thermophiles/Thermophilic Bacteria


  • Heat-loving microbes
  • Capable of growth at high temperatures
  • Minimum growth temp: 40°C
  • Maximum GT : 73 °C
  • Optimum GT : 50°C - 60°C
• Hyperthermophiles (archaeans)


  • Requires higher temp compared to the thermophilic bacterium
  • Minimum growth temp: 65°C
  • Maximum GT : 110 °C
  • Optimum GT : 80°C
• From 0°C down to - 30°C, there is no significant microbial growth
• Refrigeration prevents the growth of microorganism
• pH


  Refers to the acidity or alkalinity of a solution
• Preferred pH for bacteria to grow


  pH 6.5 - pH 7.5 (higher than 7.5 - bacteria can't grow anymore)
• Acidophiles


  • pH 4.0 or lower
• Helicobacter pylori


  • Causative agent of ulcer
  • Bacterial species that can be found in our digestive tract
  • Example of acidophiles (not all are pathogens)
• Osmotic Pressure


  It has to do with the number of H2O molecules inside and outside the bacterial cell
• Hypertonic Solution


  • An example is 10% NaCl (sodium chloride) solution
  • Undergo the process of plasmolysis (the shrinking of cytoplasm together with the plasmalemma)
• Hypotonic Solution


  • An example is lower than 0.85% NaCl solution
  • More H2O molecules outside the cell, causing it to enter the Bacterial cell
  • Causes the swelling of the Bacterial cell
  • If the Cell wall is damaged (bursting) or (lysis of BC)
  • If the CW is intact / strong (swelling)
• Isotonic Solution


  • Number of H2O molecules outside and inside the cell is EQUAL
  • Example: 0.85% or 0.9% NaCl solution (saline solution)
  • Balanced, no net movement
• Chemical requirements for microbial growth

  • Carbon
  • Nitrogen, Sulfur, and Phosphorus
  • Trace Elements
  • Oxygen
• Carbon


  The structural backbone of living matter (essential)
• Nitrogen, Sulfur, and Phosphorus

  • Nitrogen + Sulfur: Protein synthesis / Protein production
  • Nitrogen + Phosphorus: Synthesis of DNA, RNA and ATP
• Trace Elements


  • Iron, copper, molybdenum, and zinc (serves as co-factors of enzymes)
  • Needed for microbial growth
  • Help enzymes do their work, to catalyze metabolic processes
• Types of microorganisms based on oxygen requirements

  • Obligate Aerobes
  • Microaerophiles
  • Obligate Anaerobes
  • Aerotolerant Anaerobes
  • Facultative Anaerobes
• Obligate Aerobes


  • Turbid / cloudy at the surface level of the culture medium
  • Need oxygen, if oxygen is removed, they will die
  • Exhibit only aerobic growth
• Microaerophiles


  • Small amount / low conc. of oxygen - GOOD
  • Too much oxygen & zero oxygen - NOT GOOD
• Obligate Anaerobes


  • Turbidity at the bottom level
  • The presence of oxygen would kill them
  • They don't like oxygen
  • Exhibit only aerobic growth
• Aerotolerant Anaerobes


  • Even / equal turbidity
  • Will still grow with / without oxygen
  • Oxygen does not affect them
• Facultative Anaerobes


  • Top / surface level has more growth compared to the middle level / bottom level
  • Exhibit both (aerobic & anaerobic growth)
  • Will still grow with / without oxygen (but they prefer and grow best with oxygen)
• Most bacteria grow only within a limited range of temperatures, and their maximum and minimum growth temperatures are only about 30°C apart
• Refrigeration is the most common method of preserving household food supplies. It is based on the principle that microbial reproductive rates decrease at low temperatures
• Endospores formed by thermophilic bacteria are unusually heat resistant and may survive the usual heat treatment given canned goods
• Most bacteria grow best in a narrow pH range near neutrality, between pH 6.5 and 7.5
• Very few bacteria grow at an acidic pH below about pH 4
• Extreme halophiles have adapted so well to high salt concentrations that they require them for growth. In this case, they may be termed obligate halophiles
• Facultative halophiles do not require high salt concentrations but are able to grow at salt concentrations up to 2%, a concentration that inhibits the growth of many other organisms
• Nitrogen fixation - use gaseous nitrogen (N2) directly from the atmosphere
• Sulfur is used to synthesize sulfur-containing amino acids and vitamins such as thiamine and biotin
• Trace elements are usually assumed to be naturally present in tap water and other components of media
• Microbes that use molecular oxygen (aerobes) extract more energy from nutrients than microbes that do not use oxygen (anaerobes)
• Organisms that require oxygen to live are called obligate aerobes
• Phases of microbial growth curve

  • Lag Phase
  • Log Phase
  • Stationary Phase
  • Death Phase
• Lag Phase


  • Intense activity preparing for population growth, but no increase in population
  • When bacterial cells are introduced to a medium, they will adjust to that environment
  • Preparing for binary fission
  • Producing enzymes needed for binary fission
  • This period of little or no cell division
  • It can last for 1 hour or several days
  • The microbial population is undergoing a period of intense metabolic activity involving, in particular, the synthesis of enzymes and various molecules