Culture Media by Morphological Classification

Morphological Class

Protozoa

Culture Media

1 Sf1Ep medium Culturing Treponema pallidum, the bacteria that causes syphilis, in vitro is a challenge. T. pallidum is not routinely cultured in the laboratory for diagnostic purposes, in part because it cannot be grown on artificial media. However, a breakthrough in culturing T. pallidum was reported in 2018 when researchers managed to grow the bacterium in a rabbit epithelial cell line (Sf1Ep) using a medium called 'Sf1Ep medium'. It's not used for routine diagnostic purposes, but for research only. The diagnosis involves direct microscopic examination, serologic tests, molecular tests and histopathology.
2 Phenol Red Mannitol Broth This is a differential medium, used to determine an organism's ability to ferment mannitol. S. aureus, which can ferment mannitol, will change the medium from red to yellow due to acid production.
3 Blood Agar (BA) This is a nutrient-rich, differential medium that supports the growth of many organisms. S. aureus forms colonies that are round, smooth, and golden-yellow. This bacterium typically demonstrates β-hemolysis, which is complete lysis of red blood cells, resulting in a clear zone around the colonies. This hemolysis is due to the production of hemolysins by S. aureus.
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 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

Mycobacteria

Culture Media

1 Loeffler Medium A serum-based medium. M. tuberculosis colonies on Loeffler medium are small, dry, wrinkled, and off-white to yellow.
2 Petragnini Medium An egg-based medium enriched with additional nutrients to promote the growth of Mycobacterium tuberculosis. Colonies of M. tuberculosis are small, round, buff-colored, and typically take 3-4 weeks to appear.

Fungi

Culture Media

1 CHROMagar Candida This differential medium allows for the isolation and identification of Candida species based on colony color. Candida albicans usually forms green colonies on this medium.

Bacilli

Culture Media

1 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.

Cocci

Culture Media

1 Middlebrook 7H11 Agar This is a nutrient-rich medium similar to 7H10 but includes additional pyruvate for energy source, promoting more luxurious growth. The colonies of M. tuberculosis appear small, slightly domed, and rough with a butyrous consistency.
2 Petragnini Medium An egg-based medium enriched with additional nutrients to promote the growth of Mycobacterium tuberculosis. Colonies of M. tuberculosis are small, round, buff-colored, and typically take 3-4 weeks to appear.
3 Liquid Media (such as Nutrient Broth) E. coli exhibits homogenous turbid growth within 12-18 hours. After prolonged incubation, pellicles may form on the surface of the media.

Spirillum

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 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 Blood Agar (BA) E. coli colonies on this differential medium are large, circular, gray, moist, and can show β-hemolysis.

Spirochetes

Culture Media

1 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.
2 Pawlowsky Medium A potato-based medium. Growth of M. tuberculosis may be similar to that seen on the LJ Medium.