- MacConkey agar: This medium is used to select for the growth of Gram-negative bacteria, particularly enteric bacteria such as Escherichia coli and Salmonella species. It contains bile salts, which are toxic to Gram-positive bacteria, and crystal violet, which inhibits the growth of some Gram-positive bacteria.
- Eosin methylene blue (EMB) agar: This medium is used to select for the growth of Gram-negative bacteria, particularly enteric bacteria. It contains lactose, which is fermented by many Gram-negative bacteria, producing acid and gas that cause the colonies to appear pink or purple. Non-lactose fermenters, such as Salmonella typhi, appear as colorless colonies.
- Mannitol salt agar (MSA): This medium is used to select for the growth of Staphylococcus aureus, a Gram-positive bacterium that is often found in the skin and respiratory tract. It contains mannitol, a sugar that is fermented by S. aureus, producing acid and gas that cause the colonies to appear yellow. Other Staphylococci, such as S. epidermidis, do not ferment mannitol and appear as red or pink colonies.
- Cetrimide agar: This medium is used to select for the growth of Pseudomonas aeruginosa, a Gram-negative bacterium that is often found in the environment and in hospital settings. It contains cetrimide, a disinfectant that is toxic to many other bacteria but not to P. aeruginosa.
- Sabouraud dextrose agar: This medium is used to select for the growth of fungi, such as yeasts and molds. It contains dextrose, a sugar that is fermented by many fungi, and peptone, which provides nutrients for their growth.