Medical Microbiology Lab II (Medias)

Suppress the growth of unwanted microbes and encourages the growth of desired microbes via antibiotics, alcohols, salts, etc.

Allows growth of several types of microbes and displays visible differences among those microbes via certain dyes or chemicals in the media. Organisms will produce characteristic changes or growth patterns that are used for identification/differentiation.

Contains lysed sheep blood. Used to culture fastidious (i.e., having complex or particular nutritional requirements) organisms. Used to isolate organisms such as Neisseria. Not selective or differential.

Contains sheep's blood. Allows for the growth of almost all bacteria (is not selective), but is differential for hemolytic organisms. Blood cells are not lysed, unlike the chocolate agar plate. Example organism isolated: Staphylococcus aureus.

Selective for gram positive organisms. Inhibits the growth of gram negative organisms via phenylethyl alcohol, which inhibits the DNA synthesis of gram negative species. Not differential. Example of organism isolated: Staphylococcus aureus.

Selective for gram positive organisms. Inhibits the growth of gram negative organisms via colistin nalidixic acid, which inhibits protein synthesis. Not differential. Example of organism isolated: Staphylococcus aureus.

Selective only for Neisseria spp. Inhibits the growth of all other microbes via antibiotics. This plate exists because in a mixed culture, Neisseria would be out competed by the other organisms present in the culture. Isolates Neisseria spp. Not differential.

Selective for halotolerant spp. Contains 7.5% NaCl. Selective for Staphylococci, Enterococci, and Micrococci spp. Example: Staphylococcus aureus. Differential; the carbohydrate mannitol combined with a pH indicator leads to a color change in the presence of mannitol-fermenting Staphylococci.

Selective for gram negative organisms. Inhibits the growth of gram positive organisms via bile salts. Differential; the carbohydrate lactose combined with a pH indicator leads to a color change in the presence of lactose fermentors (acid that accumulates from lactose fermentation activates the dye). Used to isolate enterobacteriaceae such as Escherichia coli.

Selective for gram negative organisms. Inhibits the growth of gram positive organisms via eosin Y and methylene blue. Differential; the carbohydrate lactose combined with a green metallic sheen leads to a color change in the presence of lactose fermentors. Used to isolate fecal coliform such as Escherichia coli.

Selective for gram negative organisms. Inhibits the growth of gram positive via bile salts. Differential; contains the carbohydrates lactose and sucrose as differential carbohydrates. Sulfur is also present. Enterics (i.e., gram negative intestinal spp.) that produce acid from fermentation will turn the media yellow or salmon pink colonies. Spp. such as Salmonella, Shigella, and Proteus that do not ferment any sugars present produce blue-green colonies. Salmonella species that reduce sulfur to H2S form colonies that contain a black precipitate. Used to differentiate Salmonella and Shigella from gram negative enteric organisms.

Selective for the growth of gram negative bacteria. Inhibits the growth of gram positive bacteria via desoxycholate. Differential; the carbohydrates lactose, sucrose, and xylose are present. Organisms that ferment xylose will acidify the medium and turn it yellow. Organisms capable of removing the carboxyl group from L-lysine will produce alkaline products and turn the medium red. Organisms capable of reducing sulfur will produce a black precipitate due to H2S presence. Used to isolate Shigella and Providencia, which appear red on the medium. Salmonella would have a black precipitate.