Selective Culture Media

Selective media are designed to inhibit unwanted commensal or contaminating bacteria and help to recover pathogen from a mixture of bacteria. While selective media are agar based, enrichment media are liquid in consistency. Various approaches to make a medium selective include addition of antibiotics, dyes, chemicals, alteration of pH or a combination of these. Thayer Martin Agar used to recover N. gonorrhoeae contains Vancomycin, Colistin and Nystatin.Mannitol Salt Agar and Salt Milk Agar used to recover S.aureus contain 10% NaCl. Potassium tellurite medium used to recover C.diphtheriae contains 0.04% potassium tellurite.

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• Selectively allows certain organism to grow and inhibit others
• Lowestein Jensen media- Mycobacterium tuberculosis
• Potassium tellurite (PTA)- Corynebacterium diphtheriae
• Wilson Blair bismuth sulfite medium- salmonella typhi
• Thiosulphate Citrate Bile salt Sucrose agar- Vibrio

Basics:

• Used for growth of only selected microorganisms. Selection by
  • Adding antibiotics, prevents the growth of other cells
  • Lacking amino acids
  • May contain stains and color indicators (EMB)
• Eosin-methylene blue agar (EMB)
  • Contains methylene blue, toxic to Gram + bacteria, allowing only the growth of Gram – bacteria
• MacConkey agar (MCK)
  • For Gram – bacteria
• Buffered charcoal yeast extract agar (BCYE)
  • Selective for certain Gram – , for example Legionella.
• Mannitol salt agar (MSA)
  • Selective for Gram + bacteria
• Hektoen enteric agar (HE)
  • Shigella, Salmonella
• Thiosulfate citrate bile sucrose (TCBS)
  • Vibrio cholerae

Types of Culture Media :

There are some types of important culture or growth media used in microbiological laboratories:

• The Preservation Culture Media
• The Enrichment Culture Media
• Selective Culture Media
• Differential Culture Media
• Resuscitation Culture Media
• General Purpose Media

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