Conditions for Growth and Growth Inhibition

• Thermophile

  • heat-loving
  • optimum temp: 50-80 deg C
  • cannot grow below 5 deg C
  • has heat-resistant endospores
• Mesophile

  • thrive at moderate temperatures of 20-45 deg C
  • optimal temp is near 37 deg C or the body temperature of humans
  • most pathogenic
  • normal human microbiota
• Psychrophile

  • cold-loving
  • optimal temp: 0 and below deg C
  • causes food spoilage
  • can grow in refrigerators
• Refrigerators can be used to preserve food since it can inhibit bacterial growth

  Preservation is effective as most foodborne bacteria cannot thrive in freezing temperatures
• [TEMP] Human pathogens are mesophiles
• [TEMP] E. coli is a mesophile
• [TEMP] B. subtilis is a mesophile
• Bacteria can regulate internal pH by pumping protons in and or out of the cytoplasmic membrane
• Acidophiles

  • pH: less than 5.5
  • internal pH: 6.5
  • Example: Lactobacillus spp.
• Neutrophiles

  • pH 5-9
  • internal pH: 7.5
  • most bacteria are this kind
  • Examples: E. coli, S. aureus, and P. aeroginusa
• Alkaphiles

  • pH 8-10.5
  • internal pH: 9.5
  • Example: V. cholerae
• [pH]

  Samples: E. coli, V. parahaemolyticus, and S. aureus

  V. parahaemolyticus grows best in acid media

  All grow best in alkaline

  V. parahaemolyticus can tolerate the broadest pH range
• In decreasing pH range tolerance:

  1. V. parahaemolyticus (4.8-11.0)
  2. E. coli (4.5-9.0)
  3. S. aureus (5.0-8.5)
• Most bacteria grow best at basic pH
• Obligate aerobes

  • require oxygen
• Obligate anaerobes

  • require other substances than oxygen as hydrogen acceptor
  • sensitive to oxygen inhibition
  • can only live without oxygen
• Facultative anaerobes

  • grows best with oxygen but can grow in its absence
  • during the absence of oxygen, it relies on fermentation and anaerobic respiration
• Aerotolerant Anaerobes

  • indifferent to oxygen
  • can survive in the presence of oxygen but do not utilize it for growth
  • produce ATP through anaerobic respiration
• Microaerophiles

  • require small amounts of oxygen (around 5-15% atmospheric O2)
  • high concentrations of oxygen is inhibitory
  • produces ATP through aerobic respiration and fermentation
• Obligate aerobes can be indicated by

  • growth at the upper part of the tube
• Obligate anaerobes can be indicated by

  • growth at the lower part of the tube
• Facultative anaerobes can be indicated by

  • growth at the middle and top regions of the broth
• Microaerophiles can be indicated by

  • growth at the upper part of the broth but not at the topmost portion
• Aerotolerant anaerobes can be indicated by

  • distributed growth throughout the test tube
• Halophile

  • able to grow in hypersaline environments
  • require sodium ions for growth and metabolism
• Osmophile

  • grow in high concentrations of organic solute or environments with high osmotic pressure
• Isotonic solution - salt concentrations are equal inside and outside the cell

  Hypotonic solution - salt concentrations are lower in the environment

  Hypertonic solution - salt concentrations are higher in the environment
• Isotonic solution

  • movement of water into the cell = movement of water out of the cell
• Hypotonic solution

  • water moves into the cell, causing it to swell or burst
• Hypertonic solution

  • water moves out of the cell, causing it to shrivel or collapse
• Osmotic pressure

  • minimum pressure which needs to be applied to a solution to prevent the inward flow of water across a semipermeable membrane
• Which would survive the moist heat treatment longer, E. coli or B. subtilis?

  B. subtilis since it is a spore-forming bacteria
• Why are endospores more resistant to heat than vegetative cells?

  Endospores acquire their resistance to extreme conditions due to their spore structures that provide better resistance to high temperatures
• Since boiling water is unreliable in destroying endospores, how should one use heat in medical applications to ensure spore destruction?

  autoclaves - raises moist temperature above boiling point of water
• [UV]

  longer treatment time, less bacterial growth
• removal of the Petri dish cover leads to better inhibition since it allows the penetration of UV rays
• UV rays are used only for surface disinfection of materials because it is unable to penetrate through matter
• Iodine

  • strong oxidizing agent
  • inhibits protein function
  • oxidizes proteins, nucleotides, and fatty acids, leading to cell death
• [Anaerobiosis]

  B. subtilis - facultative anaerobes
• [Anaerobiosis]

  E. coli - facultative anaerobes