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February 20, 2013
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4.
Roll down the top film to close the 3M Petrifilm SALX Plate.
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5.
Using a gloved hand (while practicing good laboratory practices to avoid cross contamination
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and/or direct contact with the plate), gently apply a sweeping motion with even pressure onto the top
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film to remove any air bubbles in the inoculation area (figure F).
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5
P
LATE
I
NCUBATION
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Incubate plates at 41.5 ± 1.0°C for 24 hours ± 2 hours in a horizontal position with the colored side up in
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stacks of no more than 20 plates.
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I
NTERPRETATION
9
1.
Remove the 3M Petrifilm SALX Plates from the incubator andVisually examine the isolated
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colonies. See Table 2. Do not count artifact bubbles that may be present.
Note:
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Using indirect back lighting may enhance reading of colony color, discrete yellow zones, and gas
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bubbles associated with a colony
.
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2.
Presumptive positive
Salmonella
species are red to brown colonies with a yellow zone or
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associated gas bubble, or both (figure G). An associated gas bubble is defined as being located within one
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colony diameter distance from the colony (see Table 2 below).
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Table 2:
Interpretation for Presumptive Positive
Salmonella
species
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Colony Color
Colony Metabolism
Result
Red
Dark
Red
Brown
Yellow
zone
Gas bubble
Presumptive +
Presumptive +
Presumptive +
Presumptive +
Presumptive +
Presumptive +
Presumptive +
Presumptive +
Presumptive +
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Non-
Salmonella
species (figure H):
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