3M Petrifilm Instrucciones De Uso página 5

3. High concentrations of colonies on the Petrifi lm AC Plates will cause the entire growth area to become red
or pink. Occasionally, on overcrowded plates, the center may lack visible colonies, but many small colonies
can be seen on the edges. When any of these occurs, record results as too numerous to count (TNTC).
When an actual count is required, plate at a higher dilution.
4. Some organisms can liquefy the gel, allowing them to spread out and obscure the presence of other
colonies. If liquefi ed gel interferes with counting, an estimated count should be made by counting the
unaffected areas.
5. Where necessary, colonies may be isolated for further identifi cation. Lift the top fi lm and pick the colony
from the gel (see fi gure g). Test using standard procedures.
6. 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 Petrifi lm Plate "Interpretation Guide." If you have questions about
specifi c applications or procedures, please contact your offi cial 3M Microbiology representative nearest you or
visit our website at www.3m.com/foodsafety.
Specifi c Instructions for Validated Methods
SM
AOAC® Offi cial Methods (986.33 Bacteria and Coliform Counts in Milk, Dry Rehydratable Film Methods and
989.10 Bacterial and Coliforms Counts in Dairy Products, Dry Rehydratable Film Methods)
Scope of the validations: Milk and other dairy products.
Incubate Petrifi lm AC Plates 48 h ± 3 h at 32ºC ± 1ºC.
Follow guidelines provided in Interpretation section of this document.
AOAC® Offi cial Methods SM (990.12 Aerobic Plate Count in Foods, Dry Rehydratable Film Methods)
Scope of the validations: In foods.
Incubate Petrifi lm AC Plates 48 h ± 3 h at 35ºC ± 1ºC.
Follow guidelines provided in Interpretation section of this document.
AFNOR Validation certifi ed method in compliance with ISO 16140
(3M 01/1-09/89)
Use the following details when implementing the above Instructions for Use:
Scope of the validation:
All human food samples
5 in comparison to ISO 4833 4
4
Incubation
Option 1 - For testing all human food products, including dairy products and raw shellfi sh:
Incubate Petrifi lm AC Plates 72 h ± 3 h at 30ºC ± 1ºC.
Option 2 - For testing all human food products, except dairy products and raw shellfi sh:
Incubate Petrifi lm AC Plates 48 h ± 3 h at 30ºC ± 1ºC.
Interpretation
Calculate the number of microorganisms present in the test sample according to ISO 7218 for one plate
per dilution. Estimates are outside of the scope of the AFNOR Validation mark.
AFNOR
Validation
3M – 01/01 – 09/89
Alternative ANALYTICAL methods for AGRIBUSINESS
Certifi ed by AFNOR Certifi cation
www.afnor-validation.com
For more information about end of validity, please refer to AFNOR VALIDATION certifi cate available on the
web-site mentioned above
Nordval Validated Method
Scope of the validation: All human food products.
Incubate Petrifi lm AC Plates for 72 h ± 3 h at 30ºC ± 1ºC.
Refer to NordVal validation for Petrifi lm AC Plate method details.
References
1. FDA. 1998. Bacteriological Analytical Manual, 8
2. ISO 6887-1. Microbiology of food and animal feeding stuffs – Preparation of test samples, initial
suspension and decimal dilutions for microbiological examination, Part 1: General rules for the preparation
of the initial suspension and decimal dilutions
3. ISO 8261/IDF 122. Milk and milk products – General guidance for the preparation of test samples, initial
suspensions and decimal dilutions for microbiological examination.
4. ISO 4833 Microbiology of food and animal feeding stuffs – Horizontal method for the enumeration of
microorganisms - Colony-count technique at 30°C
5. ISO 16140, Microbiology of food and animal feeding stuffs – Protocol for the validation of alternative
methods
6. ISO 7218. Microbiology of food and animal feeding stuffs – General rules for microbiological examination
th ed., Revision A, Appendix 3.64.
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