Bacterial Growth Requirements

Bacterial Growth Requirements

• Bacteria need elements for creating new cell material.
• Cells require components they cannot synthesize themselves.
• Inorganic elements support cellular enzymes.
• Bacteria require an energy source.

Typical Bacterial Cell Composition

• Table 5.1 shows the percentage of key elements in the dry weight of a typical bacterial or archaeal cell.
  • Carbon makes up 50%.
  • Oxygen makes up 20%.
  • Nitrogen makes up 14%.
  • Hydrogen makes up 8%.
  • Phosphorus makes up 3%.
  • Sulfur makes up 1%.

Mineral Salts Medium Requirements

• Table 5.2 details a typical mineral salts medium for bacterial growth.
  • Includes components like NH₄Cl, NaNO₃, and various trace elements, such as ZnSO₄•7H₂O, in specific amounts, measured in milligrams per liter of water.
  • A carbon source, such as glucose, is also necessary.

Rich Media for Bacterial Growth

• Nutrient Broth is a common rich medium.
• Luria Broth is another rich medium.
• Both contain mixtures of amino acids, carbohydrates, vitamins, and other growth factors.

Defined Medium for a Particular Organism

• Table 5.3 provides an example of the components and concentrations in a defined medium, specifically for Streptococcus agalactiae (a fastidious organism).
  • Includes various amino acids, vitamins, and other essential growth factors.
  • Concentrations are measured in micrograms per milliliter (µg/mL).

Techniques for Growing Bacteria on Solid Surfaces

• Streaking plates are used to isolate bacteria.

• A sterile loop is used to spread samples on agar plates.

• Resterilize (or fresh) loop is used for each streak series.

• Streak plates of Stapholycoccus aureus are created with smooth cream colored colonies.

Spread Plate and Pour Plate Procedures

• These techniques involve distributing bacteria and media.
• Necessary for accurate bacterial analysis.

Mixed Cultures by Spread Plate Technique

• Bacterial samples of nasal mucus were diluted by spread plate method.
• Resulting colonies varied in appearance, for instance, S. capitis, S. epidemis, S. haemolyticus and S. aureus.

Combination of Spread Plate and Streaking

• Spreading and streaking are combined to isolate pure cultures.
• Dilution of culture followed by streaking yields pure cultures.

Selective/Specialized Media

• Mannitol/salt agar isolates S. aureus by inhibiting competing bacteria, using a high salt concentration and mannitol as a carbon source.
• Provides a pH indicator of acidic production.

Selective Media (MacConkey Agar)

• Bile salts and crystal violet help inhibit gram-positive bacteria.
• Lactose is used as a carbon source.
  • Colonies of lactose fermenters like E. coli are red or pink.
  • Non-fermenters have white colonies.

Agar Slants

• Used to store bacterial cultures.
• Useful for culturing strains or particular organisms for maintenance.

Techniques for Growing Bacteria in Liquid Medium

• Growth in a liquid medium are in flasks or vessels.
• Stirring promotes even distribution for consistent growth.

Growth Curve in Batch Culture

• Lag phase: cells prepare to divide, but not yet dividing.
• Exponential phase: rapid growth, a steady, constant generation time.
• Stationary phase: period where growth stops and death rate equals growth rate.
• Death phase: more cells die than reproduce.

Growth Curve in Batch Culture - Cellular Processes

• C phase: genome replicates.
• D phase: DNA separates and results in two daughter cells.

Exponential Growth

• Generation time is the time required for the bacterial population to double.

Viable Cell Count by Serial Dilution

• Serial dilutions are used to dilute a sample to an appropriate concentration for counting viable bacteria.

Cell Count by Membrane Filtration

• A liquid sample is filtered to isolate cells, and they are spread on agar for counting.

Relationship Between Light Scattering and Cell Mass

• Light scattering is relevant to counting cells, and eventually assessing cell mass.
• Light absorbance might not be proportional to a cell's mass/number of cells.

Continuous Culture in a Chemostat

• A constant supply of fresh medium and removal of waste supports continuous bacterial growth in a chemostat.

Growth in Stab Culture

• Stab cultures are used to grown bacteria in a tube of agar medium.
  • Organisms and their oxygen needs can be observed.
    • Strict aerobes, facultative anaerobes, aerotolerant species, strict anaerobes and microaerophiles all grow in slightly different ways within conditions of this culture.

Anaerobic Growth

• Anaerobic growth requires specific conditions to prevent oxygen exposure (e.g., anaerobic jars are used).
• Anaerobic glove boxes can also be used for anaerobic work.