Carolina 3M Petrifilm ColiformCount Plates Manuel d'instruction - Page 8

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4. To inoculate the medium, lift the top film. The circular gel area will adhere

to the top film (fig. 10). Tape the Petrifilm plate to a flat surface in the open

position for streaking. Streak with a sterile inoculating loop more gently

and with less pressure than you would use on a standard agar plate.

5. Incubate the plates with the gridded side down, in stacks of up to 20

plates.

Colonies may be isolated for further study or to inoculate additional

cultures. Lift the top film and pick the colony from the gel (See Method A,

step 10).

*Do not use diluents that contain citrate or sodium thiosulfate. These

substances are not found in common microbiological media such as Luria

broth or nutrient broth.

The U.S. Food and Drug Administration Bacteriological Analytical Manual

defines coliforms as gram-negative rods that produce acid and gas from

lactose fermentation. Petrifilm CC Plates contain lactose, and the top film

traps gas produced by coliform growing on the plates. Coliform colonies

are identified by the gas bubbles associated with them. All bacterial

colonies on Petrifilm CC Plates are red because of an indicator dye in the

medium. The red color helps to distinguish them from dust particles or

other environmental contaminants.

Sometimes gas bubbles are trapped when the inoculate is spread on

Petrifilm plates. These bubbles are irregularly shaped and not associated

with a bacterial colony, while gas bubbles produced by lactose-fermenting

bacteria are associated with a colony (see fig. 11.)

Figure 10

Interpretation