(h) Set the incubator at 35-37C and place the reaction vessel inside of
it. Incubate for 24-28 hours (28 hours is the maximum time limit).
NOTE:
Incubate within 30 minutes of combining the water sample with the reagent
and mixing the solution.
NOTE:
Follow the operating instructions when setting up and calibrating the
incubator.
.
(2)
Interpretation procedures.
(a) Read the sample vessels after 24 hours (up to 28 hours, if needed,
while incubation is at 35-37oC). The sample vessels will show one of two colors:
1 No color. This means that coliform and E. coli are absent,
making the water potable or safe to drink.
2 Yellow color. This means that coliforms are present and the
color will increase. Additional procedures should be performed.
(b) Place the carrier two inches from the ultra violet light in a dark area
if the color of the sample is yellow. Depending on the yellow color, one of the following
should be accomplished:
1 For a faint yellow or fluorescent coIor that you are unsure of,
compare it to the comparator (W103).
2 For a yellow color equal to or greater that the comparator,
interpret the sample to be positive.
3 For a yellow color that is slightly less than the comparator,
incubate the sample up to an additional 4 hours. The yellow color will increase if
coIiforms are present.
4 Confirm and record the coliform results.
NOTE:
The comparator should be dispensed into a vessel identical to the ones used
in the presence--absence coliform test, before comparing it to the reacted test
samples.
(3)
Disposal procedure.
(a) Open each vessel and disinfect the vessel and contents. Add a
household bleach to the top of each vessel.
(b) Cap each vessel tightly and shake or mix.
MD0160
3-10