Acetate Utilization test

Differentiate organisms based on ability to use acetate as the sole source of carbon. Generally used to differentiate Shigella spp. from Escherichia coli.

Test Principle

This test is used to differentiate an organism capable of using acetate as the sole source of carbon. Organisms capable of using sodium acetate grow on the medium, resulting in an alkaline pH, turning the indicator from green to blue.

Method

With a straight inoculating needle, inoculate acetate slant

lightly from an 18- to 24-hour culture. Do not inoculate from a

broth culture, because the growth will be too heavy.

Incubate at 35°C to 37°C for up to 7 days.

Expected Results

Positive: Medium becomes alkalinized (blue) as a result of the

growth and use of acetate

Negative: No growth or growth with no indicator change to blue

Limitations

Some strains of E. coli may use acetate at a very slow rate or not at all, resulting in a false negative reaction in the identification process.

REFERENCE:

Bailey & scotts
Diagnostical microbiology
latest edition

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