Selective Culture Media

Selective Culture 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.

• 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:
  Preservation culture media are nutrient-rich formulations used to store and maintain the viability of microorganisms for extended periods, ensuring their long-term preservation and availability for future use in laboratory settings or culture collections.
• The Enrichment Culture Media:
  These media contain additional nutrients that are designed to support the growth of fastidious microorganisms. They may also contain growth factors that are essential for the growth of certain organisms. Examples of enriched media include blood agar, chocolate agar, and thioglycollate broth.
• Selective Culture Media:
  These media contain substances that inhibit the growth of unwanted microorganisms, allowing only the desired organisms to grow. Selective media are often used to isolate specific bacteria from a mixed culture. Examples of selective media include MacConkey agar, Mannitol salt agar, and Eosin methylene blue (EMB) agar.
• Differential Culture Media:
  These media contain substances that allow the differentiation of different types of microorganisms. Differential media typically contain a pH indicator that changes color in the presence of certain metabolites. Examples of differential media include Triple Sugar Iron (TSI) agar, Kligler’s Iron Agar (KIA), and Simmons citrate agar.
• Resuscitation Culture Media:
  Resuscitation culture media are used to help revive bacteria that have been stressed or injured by environmental factors. These media typically contain nutrients and growth factors that can help promote the recovery and growth of bacterial cells.
• General Purpose Media:
  These media are designed to support the growth of a wide variety of microorganisms. They are typically made with a simple nutrient formulation that includes a source of carbon, nitrogen, and energy. Examples of general-purpose media include nutrient broth, nutrient agar, and peptone water.
• Transport media: 
  These media are designed to preserve the viability of microorganisms during transport to a laboratory. Transport media typically contain nutrients and a buffering agent that help to protect the microorganisms from environmental stresses. Examples of transport media include Stuart’s transport medium and Amies transport medium.
• Anaerobic media: 
  These media are designed to support the growth of anaerobic microorganisms. Anaerobic microorganisms require an oxygen-free environment to grow. Anaerobic media typically contain a reducing agent that removes oxygen from the medium. Examples of anaerobic media include Robertson’s cooked meat medium and Thioglycolate broth.

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