Laboratory Manual andMicrobiology in Action Biology Companies 2003 Workbook in Microbiology 7e

Table 16.1 summarizes the most commonly used enriched, selective, and differential media, indicating their purpose as primary media for the isolation of microorganisms. The table should be reviewed before performing the exercise.

Table 16.1 Culture Media for the Isolation of Pathogenic Bacteria from Clinical Specimens

Media

Classification

Selective and Differential Agent(s)

Type of Organisms Isolated

Chocolate agar

Enriched

1% hemoglobin and supplements

Most fastidious pathogens such as Neisseria and Haemophilus

Blood agar plates (BAP)

Enriched and differential

5% defibrinated sheep blood

Almost all bacteria; differential for hemolytic organisms

Mannitol salt agar (MSA)

Selective and differential

7.5% NaCl and mannitol for isolation and identification of most S. aureus strains

Staphylococci and micrococci

MacConkey agar

Selective and differential

Lactose, bile salts, neutral red, and crystal violet

Gram-negative enteric bacilli

Eosin methylene blue agar (EMB)

Selective and differential

Lactose, eosin Y, and methylene blue

Gram-negative enteric bacilli

Hektoen enteric agar (HE)

Selective and differential

Lactose, sucrose, bile salts, ferric ammonium sulfate, sodium thiosulfate, bromthymol blue, acid fuchsin

Salmonella and Shigella species (enteric pathogens)

Phenylethyl alcohol agar (PEA)

Selective

Phenylethyl alcohol (inhibits gram negatives)

Gram-positive bacteria

Colistin nalidixic acid agar (CNA)

Selective

Colistin and nalidixic acid (inhibit gram negatives)

Gram-positive bacteria

Modified Thayer-Martin agar (MTM)

Selective

Hemoglobin, growth factors, and antimicrobial agents

Pathogenic Neisseria species

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