Confirmed Test

Confirmed Test

Confirmed Test

Sometimes a false positive presumptive test is obtained. This may be due to the presence of yeasts, certain Clostridium species and some other organisms, or by bacterial associations or synergism.

In order to be certain that gas-production is due to coliforms a confirmed test must be performed. Two procedures are normally employed. In one method a drop of culture from a positive lactose broth tube is transferred to brilliant green lactose bile fermentation broth, and is incubated for 24 to 48 hours at 35°C.

The appearance of gas within 48 hrs constitues a positive confirmed test.

The dye inhibits gram positive organisms and eliminates a false presumptive test and the syngergistic reaction of gram positive and gram negative organisms growing together.

In the second method a drop of culture from the positive lactose broth is streaked on a petriplate containing, Endo's, or eosin-methylene blue agar. The appearance of nucleated colonies, with or without a metallic sheen, within 24 hours indicates a positive confirmed test.

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