Selective medium
From Wikipedia, the free encyclopedia
A selective medium is a substance (usually agar-based) which grows a specific type of microbe. Using different nutrient ratios, chemical compounds (e.g. methylene blue) and incubation times, speciation of bacteria can be performed before to use other methods for the presuntive identification of bacteria or fungus. a culture medium designed to suppress the growth of unwanted microorganisms and encourage the growth of desired ones
Contents |
[edit] Examples
- Eosin-methylen blue agar (EMB) that contains methylene blue which is toxic for Gram-positive bacteria allowing only the growth (thus selecting) of Gram negative bacteria.
- YM (Yeast and Mold) which has a low pH, deterring bacterial growth.
- Blood agar (used in strep tests), which contains beef heart blood which becomes transparent in the presence of hemolytic Streptococcus.
- MacConkey agar for Gram-negative bacteria.
- Hektoen Enteric (HE): selective for gram negative bacteria.
- Mannitol Salt Agar (MSA): selective for gram positive bacteria and differential for mannitol.
- Xylose Lysine Desoxyscholate (XLD): selective for gram negative.
[edit] Selective genes
These bacterial transgenes interact with selective growth media:
- GAL transgene:
- + growth on galactose
- - no growth on glucose
- URA3 transgene:
- + growth on uracil-deficient medium
- - no growth on FOA medium
[edit] See also
[edit] References
- Madigan, Michael, and John Martinko. Biology of Microorganisms. 4th. Upper Saddle River, NJ: Pearson Prentice Hall, 2006.
