(Lab) Culture Media

• CULTURE MEDIA

  • Solid, liquid or semi-solid [gelatinous in appearance] designed to support the growth of microorganisms
• CLASSIFICATION ACCORDING TO CONSISTENCY : Solid


  Solidifying agent is added (1.5-3% of agar); will gelatinized once set in a room temperature
• Agar is the most commonly used as solidifying agent
• CLASSIFICATION ACCORDING TO CONSISTENCY : Solid

  • Melt: ≥95°C
  • Resolidify: <50°C
  • If you leave the mixture at room temperature, it will solidify
• CLASSIFICATION ACCORDING TO CONSISTENCY : Solid (uses)

  • For the surface growth of microorganisms in order to observe colony appearance
  • For pure culture isolations
  • Storage of cultures [long-term; for research; supply bacteria in school, universities, laboratories, etc.]
  • To observe specific biochemical reactions [can appear as color-changes or changes in odor]
• CLASSIFICATION ACCORDING TO CONSISTENCY : Liquid or Broth

  • Dissolved in water : Culture media that is completely dissolved in water and will never solidify
  • Uses:
  • Can be used to propagate large numbers of microorganisms in fermentation studies [one way that bacteria eat; fermentation of carbohydrates to produce by-products]
  • For various biochemical tests [which there will be color changes or changes in other properties such as pH]
  • Growth: turbidity
  • No Growth: clarity [if there’s no change in clarity, there is no growth]
• Semi-solid


  Classification according to consistency
• CLASSIFICATION ACCORDING TO CONSISTENCY : Semi-solid

  • Solidify agent is added (<1.5% of agar)
  • Has smaller concentration of agar compared to solid [not as dense, so its purpose is to determine bacterial motility]
• CLASSIFICATION ACCORDING TO CONSISTENCY : Semi-solid (uses)

  • Fermentation studies
  • In determining bacterial motility [how the bacteria migrates from the area it is introduced]
  • Promoting anaerobic growth [the deeper you go, there will be lesser oxygen]
• CLASSIFICATION ACCORDING TO CONSISTENCY : Semi-solid (uses)

  • In the negative tube : There is a straight line [discolored], so it is negative for motility (the bacteria is non-motile); the growth only occurred at the site of inoculation
• CLASSIFICATION ACCORDING TO CONSISTENCY : Semi-solid (uses)

  • In the positive tube : It is positive for motility [fainter but thicker line]
• CLASSIFICATION ACCORDING TO FUNCTION : ENRICHMENT MEDIA

  • Contains specific nutrients required for growth of particular bacterial pathogens
  • Used to enhance the growth of particular pathogen form a mixture of organism by using nutrient specificity
• CLASSIFICATION ACCORDING TO FUNCTION : SELECTIVE MEDIA

  • Favour the growth of a particular bacterium by inhibiting the growth of undesired bacteria band allowing the growth of desired bacteria
  • Will only choose a specific type
  • Kills off other types of bacteria and will only promote growth of a certain type
  • Good example is the mahogany agar of gram negative organisms only
• CLASSIFICATION ACCORDING TO FUNCTION : ENRICHED MEDIUM

  • Enriched usually by adding blood, or eggs
  • Already dehydrated, and already mixed with the mixture.
• CLASSIFICATION ACCORDING TO FUNCTION : SUPPORTIVE OR NONSELECTIVE MEDIUM

  • Contain nutrients to support growth of most nonfastidious organisms without giving any particular organism a growth advantage
• CLASSIFICATION ACCORDING TO FUNCTION : DIFFERENTIAL MEDIUM

  • Used to distinguish them from other bacteria growing on the same agar plate
  • Differentiate different types of bacteria based on appearance
• BASIC WAYS OF STERILIZATION OF MEDIA : AUTOCLAVING

  • Exposure to steam at 121°C and 15 lbs of pressure of 15 minutes or longer, depending on the nature of the item
  • Uses steam under pressure
  • Microorganisms, even endospores, will not survive longer than about 12 to 13 minutes
• BASIC WAYS OF STERILIZATION OF MEDIA : ULTRAVIOLET (UV) RADIATION

  • Around 260nm is quite lethal to many organisms but does not penetrate glass, dirt films, water, and other substances very effectively
  • Biosafety cabinet has usually uv lamps attached to it
• BASIC WAYS OF STERILIZATION OF MEDIA : ETHYLENE OXIDE

  • Both microbicidal and sporicidal and kills by covalently attaching to cell proteins
  • It is particularly effective sterilizing agent because it rapidly penetrates packing materials, even plastic wraps
• Plated Media Steps

  1. Weight
  2. Dissolve
  3. Sterilize
  4. Dispense
• Tube Media Steps

  1. Weigh
  2. Dissolve
  3. Dispense
  4. Sterilize