are used for the growth of only select microorganisms. For example, if a microorganism is resistant to a certain antibiotic, such as ampicillin or tetracycline, then that antibiotic can be added to the medium in order to prevent other cells, which do not possess the resistance, from growing. Media lacking an amino acid such as proline in conjunction with E. coli unable to synthesize it were commonly used by geneticists before the emergence of genomics to map bacterial chromosomes.Selective growth media are also used in cell culture to ensure the survival or proliferation of cells with certain properties, such as antibiotic resistance or the ability to synthesize a certain metabolite. Normally, the presence of a specific gene or an allele of a gene confers upon the cell the ability to grow in the selective medium. In such cases, the gene is termed a marker.
Selective growth media for eukaryotic cells commonly contain neomycin to select cells that have been successfully transfected with a plasmid carrying the neomycin resistance gene as a marker. Gancyclovir is an exception to the rule as it is used to specifically kill cells that carry its respective marker, the Herpes simplex virus thymidine kinase (HSV TK).
Some examples of selective media include:
eosin-methylen blue agar (EMB) that contains methylene blue – toxic to Gram-positive bacteria, allowing only the growth 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 that becomes transparent in the presence of hemolytic Streptococcus
MacConkey agar for Gram-negative bacteria
Hektoen Enteric (HE) which is selective for Gram-negative bacteria
Mannitol Salt Agar (MSA) which is selective for Gram-positive bacteria and differential for mannitol
xylose lysine desoxyscholate (XLD), which is selective for Gram-negative bacteria
Buffered charcoal yeast extract agar, which is selective for certain gram-negative bacteria, especially Legionella pneumophila
eosin-methylen blue agar (EMB) that contains methylene blue – toxic to Gram-positive bacteria, allowing only the growth 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 that becomes transparent in the presence of hemolytic Streptococcus
MacConkey agar for Gram-negative bacteria
Hektoen Enteric (HE) which is selective for Gram-negative bacteria
Mannitol Salt Agar (MSA) which is selective for Gram-positive bacteria and differential for mannitol
xylose lysine desoxyscholate (XLD), which is selective for Gram-negative bacteria
Buffered charcoal yeast extract agar, which is selective for certain gram-negative bacteria, especially Legionella pneumophila