3M Petrifilm E. coli/coliform Count Plate 2 3 No growth = 0 Notice the changes in gel color in figures 2 through 8. As the E. coli or coliform count i

Size: px

Start display at page:

Download "3M Petrifilm E. coli/coliform Count Plate 2 3 No growth = 0 Notice the changes in gel color in figures 2 through 8. As the E. coli or coliform count i"

钱学历
6 years ago
Views:

3 Petrifilm E.coli/Coliform Count Plate Interpretation Guide This guide familiarizes you with results on 3M Petrifilm E. coli/coliform Count plates.

1 3 Petrifilm E.coli/Coliform Count Plate Interpretation Guide This guide familiarizes you with results on 3M Petrifilm E. coli/coliform Count plates. For more information, contact the official 3M Microbiology Products representative nearest you. Petrifilm E. coli/coliform Count (EC) plates contain Violet Red Bile (VRB) nutrients, a cold-water-soluble gelling agent, an indicator of glucuronidase activity, and an indicator that facilitates colony enumeration. Most E. coli (about 97%) produce beta-glucuronidase which produces a blue precipitate associated with the colony. The top film traps gas produced by the lactose fermenting coliforms and E. coli. About 95% of E. coli produce gas, indicated by blue to red-blue colonies associated with entrapped gas on the Petrifilm EC plate (within approximately one colony diameter). AOAC INTERNATIONAL and U.S. FDA Bacteriological Analytical Manual (BAM) define coliforms as gram-negative rods which produce acid and gas from lactose during metabolic fermentation. Coliform colonies growing on the Petrifilm EC plate produce acid which causes the ph indicator to make the gel color darker red. Gas trapped around red coliform colonies indicates confirmed coliforms. The identification of E. coli may vary by country (see Reminders for Use section for incubation times and temperatures): AOAC INTERNATIONAL validated method E. coli = 49 (blue colonies with gas) Total coliform = 87 (red and blue colonies with gas) Do not use this plate alone for the detection of E. coli O57. Like most other E. coli/coliform media, this plate will not specifically indicate whether any O57 strain is present.

3M Petrifilm E. coli/coliform Count Plate 2 3 No growth = 0 Notice the changes in gel color in figures 2 through 8. As the E.

Background bubbles are a characteristic of the gel and are not a result of E.

coli count = 3 Total coliform count = 28 The counting range for the total population on Petrifilm EC plates is 5 50.

See circle. Back Lighting Front Lighting 2 E. coli count = 3 Any blue in a colony (blue to red-blue) indicates the presence of E.

Circle shows a red-blue colony counted using back lighting. Circle 2 shows the same colony with front lighting.

2 3M Petrifilm E. coli/coliform Count Plate 2 3 No growth = 0 Notice the changes in gel color in figures 2 through 8. As the E. coli or coliform count increases, the color of the gel turns to dark red or purple-blue. Background bubbles are a characteristic of the gel and are not a result of E. coli or coliform growth. See square. E. coli count = 3 Total coliform count = 28 The counting range for the total population on Petrifilm EC plates is Do not count colonies that appear on the foam barrier because they are removed from the selective influence of the medium. See circle. Back Lighting Front Lighting 2 E. coli count = 3 Any blue in a colony (blue to red-blue) indicates the presence of E. coli. Front lighting will enhance the detection of blue precipitate formed by a colony. Circle shows a red-blue colony counted using back lighting. Circle 2 shows the same colony with front lighting. The blue precipitate is more evident in circle 2. 4 E. coli count = 7 Estimated total coliform count = 50 The circular growth area is approximately 20 cm 2. Estimates can be made on plates containing greater than 50 colonies by counting the number of colonies in one or more representative squares and determining the average number per square. Multiply the average number by 20 to determine the estimated count per plate. 5

TNTC (Too Numerous to Count) To obtain a more accurate count, dilute the sample further.

characteristics: many small colonies, many gas bubbles, and a deepening of the gel color from red to

strains of E. coli may produce less gas and blue colonies may be less definitive.

3 TNTC (Too Numerous to Count) To obtain a more accurate count, dilute the sample further. 6 7 Actual count ~ 0 6 Petrifilm EC plates with colonies that are TNTC have one or more of the following characteristics: many small colonies, many gas bubbles, and a deepening of the gel color from red to purple-blue. Actual count ~ 0 8 High concentrations of E. coli may cause the growth area to turn purple-blue. Presumptive E. coli count ~ 8 Estimated total coliform count ~ 0 8 When high levels of coliforms are present (>0 8 ), some strains of E. coli may produce less gas and blue colonies may be less definitive. Count all blue colonies without gas and/or blue zones as presumptive E. coli. Pick blue colonies without gas and confirm if necessary. 8 Actual count ~ 0 8 When high numbers of non-coliform organisms such as Pseudomonas are present on Petrifilm EC plates, the gel may turn yellow. 9

Bubbles 3 2 0 Total coliform count = 3 Food particles are irregularly shaped and are not associated with gas bubbles.

Artifact bubbles may result from improper inoculation or from trapped air within the sample.

4 Bubbles Total coliform count = 3 Food particles are irregularly shaped and are not associated with gas bubbles. Total coliform count = 78 Bubble patterns may vary. Gas may disrupt the colony so that the colony outlines the bubble. See circles and 2. Artifact bubbles may result from improper inoculation or from trapped air within the sample. They are irregularly shaped and are not associated with a colony. See circle Examples 0 show various bubble patterns associated with gas producing colonies. All should be enumerated.

5 3Petrifilm E. coli / Coliform Count Plates Reminders for Use For detailed WARNING, CAUTIONS, DISCLAIMER OF WARRANTIES / LIMITED REMEDY, LIMITATION OF 3M LIABILITY, STORAGE AND DISPOSAL information, and INSTRUCTIONS FOR USE see Product s package insert. Storage Petrifilm Petrifilm Petrifilm Store unopened packages at 8 C To seal opened package, fold end 2 3 ( 46 F). Use before expiration date on over and tape shut. package. In areas of high humidity where condensate may be an issue, it is best to allow packages to reach room temperature before opening. Sample Preparation Keep resealed package at 25 C ( 77 F) and <50%RH. Do not refrigerate opened packages. Use Petrifilm plates within one month after opening Prepare a :0 or greater dilution of food product. Weigh or pipette food product into an appropriate container such as a stomacher bag, dilution bottle, Whirl-Pak bag, or other sterile container. Add appropriate quantity of one of the following sterile diluents: Butterfield's phosphate buffer (IDF phosphate buffer, g/l of KH 2 PO 4 adjusted to ph 7.2), 0.% peptone water, peptone salt diluent (ISO method 6887), buffered peptone water (ISO method 6887-), saline solution ( %), bisulfite-free letheen broth, or distilled water. Do not use buffers containing citrate, bisulfite, or thiosulfate; they can inhibit growth. Blend or homogenize sample per current procedure. Adjust ph of the diluted sample between 6.5 and 7.5. for acid products, use N NaOH, for alkaline products, use N HCI. Inoculation Place Petrifilm plate on level With pipette perpendicular to surface. Lift top film. Petrifilm plate, place ml of sample onto center of bottom film. Carefully ROLL top film down to avoid entrapping air bubbles. Do NOT let top film drop.

6 RIDGE side FLAT side With FLAT side down, place spreader on top film over inoculum. Incubation 2 one minute for gel to solidify. GENTLY apply pressure on spreader to distribute inoculum over circular area before gel is formed. Do not twist or slide the spreader. Interpretation Lift spreader. Wait a minimum of <70 F 3 Incubate plates with clear side up in stacks of no more than 20. It may be necessary to humidify incubator to minimize moisture loss. Incubation time and temperature varies by method. Most common approved methods: Petrifilm plates can be counted on a Colonies may be isolated for further 4 5 standard colony counter or other identification. Lift top film and pick illuminated magnifier. Refer to the the colony from the gel. Interpretation Guide section when reading results. AOAC Official Method 99.4 for coliforms: incubate 24h ± 2h at 35 C ± C for E.coli: incubate 48h ± 2h at 35 C ± C AOAC Official Method for E.coli (for meat, poultry and seafood): incubate 24h ± 2h at 35 C ± C NMKL method (47.993) for coliforms: incubate 24h ± 2h at 37 C for E.coli: incubate 48h ± 2h at 37 C Additional Comments Questions? U.S., Call , Canada, call x6574 for technical service. To order Petrifilm plates in the U.S., call Latin America / Africa and Asia Pacific regions, call Microbiology Products 3M Center Bldg W-05 St. Paul, MN USA microbiology@mmm.com 3M Canada Post Office Box 5757 London, Ontario N6A4T Canada M Europe Laboratoires 3M Santé Boulevard de l Oise Cergy Pontoise Cedex France Recycled Paper 40% pre-consumer 0% post-consumer Petrifilm is a trademark of 3M. Whirl-Pak is a registered trademark of NASCO. Printed in U.S.A. 3M (2) DPI

M Petrifilm Coliform Count Plate 2 No growth = 0 Notice the changes in gel color in figures 2 through 5. As the coliform count increases, the gel colo

Petrifilm Coliform Count Plate Interpretation Guide This guide familiarizes you with results on M Petrifilm Coliform Count plates. For more information, contact the official M Microbiology Products representative