Sample Preparation - 3M Petrifilm 6402 Manual Del Usuario

To store opened pouches in a freezer, place Petrifilm Plates in a sealable container. To remove frozen Petrifilm Plates for use, open the container,
remove the plates that are needed and immediately return remaining plates to the freezer in the sealed container. Plates should not be used past
their expiration date. The freezer that is used for open pouch storage must not have an automatic defrost cycle as this would repeatedly expose
the plates to moisture which can damage the plates.
Do not use plates that show orange or brown discoloration. Expiration date and lot number are noted on each package of Petrifilm Plates.
The lot number is also noted on individual plates.
After use, Petrifilm RCC Plates may contain microorganisms that may be a potential biohazard. Follow current industry standards for disposal.
INSTRUCTIONS FOR USE

Sample Preparation

1. Use appropriate sterile diluents:
Butterfield's phosphate buffer
or distilled water.
Do not use diluents containing citrate, bisulfite or thiosulfate with Petrifilm Plates; they can inhibit growth. If citrate buffer
is indicated in the standard procedure, substitute with one of the buffers listed above, warmed to 40-45°C (104-113°F).
2. Blend or homogenize sample.
3. For optimal growth and recovery of microorganisms, adjust the pH of the sample suspension to 6.5 - 7.5. For acidic products, adjust the pH
with 1N NaOH. For alkaline products, adjust the pH with 1N HCl.
Plating
1. Place the Petrifilm RCC Plate on a flat, level surface (see figure a).
2. Lift the top film and with the pipette perpendicular dispense 1 mL of sample suspension onto the center of bottom film (see figure b).
3. Roll the top film down onto the sample to prevent trapping air bubbles (see figure c).
4. Place the plastic spreader with the flat side down on the center of the plate (see figure d). Press gently on the center of the spreader to
distribute the sample evenly. Spread the inoculum over the entire Petrifilm Plate growth area before the gel is formed. Do not slide the
spreader across the film.
5. Remove the spreader and leave the plate undisturbed for at least one minute to permit the gel to form.
Incubation
1. Incubate plates in a horizontal position with the clear side up in stacks of no more than 20 plates. Several incubation times and temperatures
can be used depending on current local reference methods, some of which are listed in the section below titled Specific Instructions for
Validated Methods. **See AFNOR incubation temperature exception for processed pork.
2. Examine plates for coliform growth at any time during a 24 h ± 2 h incubation interval depending on the desired information and method
being followed (described below*). Because coliform growth is affected by temperature, time out of the incubator should be minimized to
avoid extending the detection time.
Interpretation and Enumeration
For interpretation see section "Specific Instructions for Validated Methods"
1. Indirect back lighting may enhance early detection of yellow acid zones on Petrifilm RCC Plates. Coliform colonies may begin to appear
at 6 h of incubation as discrete yellow zones indicating colony forming units (CFUs) (see figure e). Continue incubating plates to detect
additional acid zones and/or red colonies associated with acid. Do not count colonies on the foam dam since they are removed from the
selective influence of the medium. Do not count artifact bubbles that may be present.
Some coliforms produce large amounts of acid. For these organisms, fusion of the yellow acid zones could occur at about twenty colonies
per plate. The circular growth area is approximately 20 cm². Estimates can be made on plates containing greater than 50 acid zones by
counting the number of acid zones in one or more representative squares and determining the average number per square. Multiply the
average number by 20 to determine total count per plate.
2. Where necessary, colonies may be isolated for further identification. Lift the top film and pick the colony from the gel (see figure h).
Test using standard procedures.
3. If the plates cannot be counted within 1 hour of removal from the incubator, they may be stored for later enumeration by freezing
in a sealable container at temperatures lower than or equal to minus 15°C (5°F) for no longer than one week.
For further information refer to the appropriate 3M™ Petrifilm™ Plate "Interpretation Guide." If you have questions about specific applications
or procedures, please contact your official 3M Microbiology representative nearest you or visit our website at www.3m.com/microbiology.
, 0.1% peptone water , peptone salt diluent
1, 3 3
, saline solution (0.85-0.90%), bisulfite-free letheen broth,
2, 3
2