SELECTIVE MEDIUM AS A TOOL TO ISOLATE AND CHARACTERIZE BACTERIA
- 1. Selective medium “In the world of microbes, small things can have a big impact.”
- 2. What is Selective Medium A type of culture medium specifically designed to allow the growth of only certain desired microorganisms while inhibiting the growth of unwanted organisms
- 3. By using selective media, microbiologists can easily isolate and study specific bacterial species from samples that contain diverse microbial communities. SELECTIVE MEDIUM Fungi are more closely related to animals than plants, despite their often plant-like appearances.
- 4. HOW IS SELECTIVITY ACHIEVED Selectivity is achieved by adding components like: antibiotics Stains Salts Chemicals
- 5. EXAMPLES OF SELECTIVE MEDIA Components of MacCONKEY Medium: BILE SALTS Bile salts and crystal violet which are present prevent the growth of gram-positive bacteria. The media detects lactose fermentation by enteric bacteria with the pH indicator neutral red MacConkey agar MacConkey agar is both a selective and a differential medium for Gram-negative rods which ferment Lactose Lactose fermenters turn red or pink on MacConkey agar, and non-fermenters do not change colour Bile salts Crystal violet Lactose Neutral red as a pH indicator
- 7. MSA is a commonly used selective growth medium in microbiology. It contains a high concentration of salt (NaCl) which is inhibitory to most bacteria This makes MSA selective against most Gram- negative and selective for some Gram-positive bacteria that tolerate high salt concentrations Micro organisms that ferment Mannitol will appear as yellow colonies whilst those which do not will be pink MANNITOL SALT AGAR S. aureus S. epidermidis Micrococcaceae
- 8. REFERENCES Al-blooshi, S.Y., Latif, M.A.A., Sabaneh, N.K. et al. Development of a novel selective medium for culture of Gram- negative bacteria. BMC Res Notes 14, 211 (2021). https://doi.org/10.1186/s13104-021-05628-2 Biotrend (no date) Biotrend. Available at: https://www.biotrend.com/en/buy/cat-selective-media-for-microbiology- 5510.html#:~:text=A%20selective%20medium%20is%20a,as%20food%20and%20dairy%20laboratories. (Accessed: 27 January 2025). Libretexts (2023) 1.29: Mannitol Salt Agar, Biology LibreTexts. Available at: https://bio.libretexts.org/Bookshelves/Microbiology/Microbiology_Laboratory_Manual_(Hartline)/01%3A_Labs/ 1.29%3A_Mannitol_Salt_Agar (Accessed: 27 January 2025). Macconkey, A.T. (1908) Bile Salt Media and their advantages in some bacteriological examinations, The Journal of hygiene. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC2167122/ (Accessed: 27 January 2025). Prinzi, A. and Rohde, R. (no date) Why Differential & Selective Media remain invaluable tools, ASM.org. Available at: https://asm.org/articles/2020/september/why-differential-selective-media-are-invaluable-to#:~:text=Selective %20media%20are%20used%20to,are%20not%20resistant%2C%20from%20growing. (Accessed: 27 January 2025).