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.

Explore the essential requirements for bacterial growth, including the key elements needed for cell composition and the specific mineral salts required in different media. This quiz highlights the importance of various components like carbon, nitrogen, and rich media for effective bacterial culture. Test your knowledge on the vital nutrients that support microbial life!