VMC 211: General Veterinary Microbiology (1+1)

MEDIA

• The media used for bacterial culture work should not contain any contaminating organism. The media are normally sterilized by autoclaving.
• Certain media containing sugar (glucose) should be autoclaved at a lower temperature for longer duration (110C for 30 minutes).
• The solidifying agent used in media is agar obtained from sea weed. Depending on the percentage of agar the media are divided in to solid and semisolid. Medium not containing agar is called liquid medium or broth.
• Media can be prepared by adding the different constituents in distilled water followed by sterilization.Now ready made media are available which can be prepared by dissolving them in distilled water as per the manufacturer’s instructions and sterilization.
• Different types media are available to serve specific purposes in the clinical lab. The media are classified into General purpose/basal media, enriched, differential and selective media.
  • General purpose/basal media
  • Enriched media: They have one or more added substances to increase the likelihood of growth of fastidious organisms. The commonly added substances include blood, serum or vitamins.
  • Differential media: They are used to distinguish types of bacteria. This done by addition of substances that will be changed as a result of a metabolic activity of the bacteria eg: MacConkey agar. Eosin-Methylene blue agar.
  • Selective media: They are ones in which a particular organism is selected while others are inhibited.