Culture Media by Morphological Classification

Morphological Class

Protozoa

Culture Media

1 DNase Test Agar S. aureus produces the enzyme DNase which hydrolyses DNA. When S. aureus grows on this medium, the DNA is broken down, which can be visualised using a hydrochloric acid (HCl) solution: clear zones around the colonies indicate DNA breakdown.
2 Sula’s Medium A liquid medium containing glycerol, asparagine, and a variety of salts. The growth of M. tuberculosis results in turbidity.
3 Loeffler Medium A serum-based medium. M. tuberculosis colonies on Loeffler medium are small, dry, wrinkled, and off-white to yellow.

Mycobacteria

Culture Media

1 Baird-Parker Agar (BPA) his is a selective medium for the isolation of Staphylococcus species. It has lithium chloride and glycine to inhibit the growth of Gram-negative bacteria and most Gram-positive bacteria except Staphylococcus. Egg yolk emulsion is added to detect lecithinase production and tellurite reduction. S. aureus colonies on BPA are black due to reduction of tellurite, and they exhibit a clear zone due to lecithinase activity on egg yolk.
2 Tarshis Medium A blood-based medium that can promote the growth of M. tuberculosis. The colonies appear similar to those on the LJ Medium.

Fungi

Culture Media

1 Sula’s Medium A liquid medium containing glycerol, asparagine, and a variety of salts. The growth of M. tuberculosis results in turbidity.
2 Middlebrook 7H9 Broth This is a liquid medium that contains glycerol and Tween 80, which prevent clumping of mycobacteria. The growth of M. tuberculosis results in turbidity.
3 Tarshis Medium A blood-based medium that can promote the growth of M. tuberculosis. The colonies appear similar to those on the LJ Medium.
4 Violet Red Bile Agar (VRBA) E. coli colonies are red (pink to red) and may show bluish fluorescence under UV light.
5 Eosin Methylene Blue (EMB) Agar A selective and differential medium where E. coli forms distinctive metallic green sheen colonies due to vigorous lactose fermentation.
6 Nickerson’s Medium or Bismuth Sulfite Glucose Glycine Yeast (BSGG) This medium is used to stimulate the production of germ tubes, a characteristic of Candida albicans.
7 Blood Agar A differential medium used to identify bacteria based on their hemolytic properties. E. faecalis typically shows gamma-hemolysis on this medium, i.e., no hemolysis or change in the color of the medium.
8 Bile Esculin Agar (BEA) A selective and differential medium that differentiates group D Streptococci and Enterococci based on the ability to hydrolyze esculin in the presence of bile. E. faecalis hydrolyzes esculin, leading to the formation of a dark brown or black precipita

Bacilli

Culture Media

1 Middlebrook 7H9 Broth This is a liquid medium that contains glycerol and Tween 80, which prevent clumping of mycobacteria. The growth of M. tuberculosis results in turbidity.
2 Violet Red Bile Agar (VRBA) E. coli colonies are red (pink to red) and may show bluish fluorescence under UV light.
3 Bile Esculin Agar (BEA) A selective and differential medium that differentiates group D Streptococci and Enterococci based on the ability to hydrolyze esculin in the presence of bile. E. faecalis hydrolyzes esculin, leading to the formation of a dark brown or black precipita
4 Brain-Heart Infusion (BHI) Broth or Agar This is a nutrient-rich medium that supports the growth of a variety of fastidious organisms, including E. faecalis. The typical phenotype of E. faecalis on BHI is small, round, and white colonies.

Cocci

Culture Media

1 Middlebrook 7H9 Broth This is a liquid medium that contains glycerol and Tween 80, which prevent clumping of mycobacteria. The growth of M. tuberculosis results in turbidity.
2 Tryptic Soy Agar (TSA) A general purpose medium. E. coli colonies are medium to large, with a shiny moist appearance.
3 Eosin Methylene Blue (EMB) Agar A selective and differential medium where E. coli forms distinctive metallic green sheen colonies due to vigorous lactose fermentation.
4 Potato Dextrose Agar (PDA) Potato Dextrose Agar (PDA) consists of a nutrient-rich substrate, made from dehydrated Potato Infusion and Dextrose, ideal for robust mycological propagation. Agar provides the solidifying medium. Acidification, typically using sterile tartaric acid, adjusts the pH to 3.5 +/- 0.1 to create a more selective environment by inhibiting bacterial proliferation. Additionally, Chloramphenicol is incorporated as an antimicrobial agent to further suppress bacterial contamination, thereby facilitating the selective isolation of fungi.
5 Sabouraud Dextrose Agar (SDA) It is composed of peptone, dextrose (glucose), and agar. The high dextrose concentration promotes fungal growth, while the acidic pH inhibits bacterial growth.
6 Tryptic Soy Broth or Agar (TSB/TSA) A general-purpose medium that supports the growth of a broad spectrum of bacteria. E. faecalis on TSA will typically form small, round, and white colonies, indicating a positive growth.

Spirillum

Culture Media

1 Mannitol Salt Agar (MSA), or Chapman Agar This is a selective and differential medium. The high concentration of NaCl (~7.5%) selects for halophiles, organisms that can tolerate high salt concentrations, thereby favouring the growth of Staphylococcus species. Mannitol is the differential component: S. aureus ferments mannitol, lowering the pH of the medium, which results in a color change of the pH indicator from red to yellow. Thus, growth of S. aureus is indicated by yellow colonies.
2 Sauton’s Medium A liquid medium that lacks detergents, which helps in the formation of corded colonies. When M. tuberculosis grows in this medium, it results in turbidity.
3 Triple Sugar Iron (TSI) Agar E. coli typically produces an acid butt, acid slant, and gas, with no H2S production, indicating it ferments lactose, sucrose, and glucose.
4 Nickerson’s Medium or Bismuth Sulfite Glucose Glycine Yeast (BSGG) This medium is used to stimulate the production of germ tubes, a characteristic of Candida albicans.
5 Todd-Hewitt Broth A liquid enrichment medium used for the cultivation of fastidious organisms such as streptococci and enterococci. E. faecalis will lead to a turbid broth due to microbial growth.
6 Bile Esculin Agar (BEA) A selective and differential medium that differentiates group D Streptococci and Enterococci based on the ability to hydrolyze esculin in the presence of bile. E. faecalis hydrolyzes esculin, leading to the formation of a dark brown or black precipita

Spirochetes

Culture Media

1 Middlebrook 7H9 Broth This is a liquid medium that contains glycerol and Tween 80, which prevent clumping of mycobacteria. The growth of M. tuberculosis results in turbidity.
2 Dubos’ Medium A liquid medium that contains a mixture of salts, fatty acids, and polysorbate. When M. tuberculosis grows in this medium, it causes the medium to become turbid.
3 Loeffler Medium A serum-based medium. M. tuberculosis colonies on Loeffler medium are small, dry, wrinkled, and off-white to yellow.
4 Urea Agar/Broth E. coli is typically urease negative, so no color change would be expected in this medium.
5 Tryptic Soy Agar (TSA) A general purpose medium. E. coli colonies are medium to large, with a shiny moist appearance.
6 RPMI 1640 Medium It is a rich medium that contains inorganic salts, glucose, amino acids, vitamins, and other nutrients that promote the growth of yeast cells.