3M Food SafetyAerobic Procedure for Lactic Acid Bacteria with 3M™ Petrifilm™ Aerobic Count Plates for Monitoring Food and the Environment

The Aerobic Procedure for Lactic Acid Bacteria utilizes the

3M™ Petrifilm™ Aerobic Count Plate supplemented with MRS

(deMan, Rogosa and Sharpe) medium and a pH indicator to

help identify and enumerate lactic acid bacteria in food and

environmental samples. Food processors and reference labs

have demonstrated feasibility relative to their current lactic

acid bacteria testing procedure. This guide was developed to

aid food processors in validating this method.

Interpretation Guide

ProductivityMaximized

Technician

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Interpretation Guide: Aerobic Procedure for Lactic Acid Bacteria with 3M™ Petrifilm™ Plates for Monitoring Food and Environment

Lactic Acid Bacteria Count: 8 A red indicator dye reacts with growing bacteria allowing colony visualization. Acid-producing bacteria produce a yellow zone (halo) around the colony.

Bacteria shown in Figure 1: Lactococcus

Figure 1

Lactic Acid Bacteria Count: 0 Negative Control Plate containing 0.5mL Aerobic Lactic Acid Bacteria Broth plus 0.5mL diluent.

Figure 2

Lactic Acid Bacteria Count: 15 Colony color can vary from faint to dark pink depending on organism, environmental stress and sample matrix.

Bacteria shown in Figure 3: Lactobacillus

Figure 3

Lactic Acid Bacteria Count: 11 Colony-associated bubbles, which may appear whiter than the background, can indicate gas production.

Bacteria shown in Figure 4: Weisella

Figure 4

User’s Responsibilities: 3M Petrifilm Plate performance has not been evaluated with all combinations of microbial flora, incubation conditions and food matrixes. It is the user’s responsibility to determine that any test methods and results meet the user’s requirements.

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Red colonies are sometimes fainter and smaller near the edge of the inoculated area.

Bacteria shown in Figure 5: Streptococcus agglacati

Figure 5

Lactic Acid Bacteria Count: 7 Some lactic acid bacteria produce yellow zones (halos) before colonies are visible.

Bacteria shown in Figure 6: Streptococcus oralis

Figure 6

The presence of high levels of acid, whether produced by lactic acid bacteria or associated with the sample matrix, can turn the inoculation area yellow.

Figure 7

Incubation conditions (time and temperature) or additional dilution may make it easier to identify and enumerate lactic acid bacteria.

Figure 8

User’s Responsibilities: 3M Petrifilm Plate performance has not been evaluated with all combinations of microbial flora, incubation conditions and food matrixes. It is the user’s responsibility to determine that any test methods and results meet the user’s requirements.

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Backlighting can aid in enumerating faint colonies or colonies in a low pH (yellow) background.

Figure 9

Ham Salad Food particles can be distinguished from colonies by their irregular shape and darker red color.

Figure 10

Non-lactic acid producing bacteria typically appear as red colonies against a red background. Additional incubation may change the color of the background.

Bacteria shown in Figure 11: Pseudomonas

Figure 11

Non-lactic acid producing bacteria typically appear as red colonies against a red background. Additional incubation may change the color of the background.

Bacteria shown in Figure 12: E. coli

Figure 12

User’s Responsibilities: 3M Petrifilm Plate performance has not been evaluated with all combinations of microbial flora, incubation conditions and food matrixes. It is the user’s responsibility to determine that any test methods and results meet the user’s requirements.

Reminders for Use

** 3M™ Quick Swab and Swab Samplers with either DE Neutralizing Broth or Letheen Broth are available from 3M.

1:10 or Greater Dilution of Food Sample

Food Sample Procedure

Weigh or pipette food product into an appropriate container.

1 Add appropriate diluent.2 Blend or homogenize sample per current procedure.

3 Place 3M™ Petrifilm™ Aerobic Count Plate (AC) on level surface. Lift top film.

4

Using a diluting pipettor, combine 0.5mL of Aerobic Lactic Acid Bacteria Broth (MRS and Chlorophenol Red) with 0.5mL diluted food sample within the pipette tip.

20

15

107.5.5

30

25

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Mix lactic broth plus swab solutions in equal volumes.

20

15

107.5.5

30

25

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With pipettor perpendicular to 3M™ Petrifilm™ AC Plate, place entire 1mL of sample onto center of bottom film.

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With pipettor perpendicular to 3M™ Petrifilm™ AC Plate, place entire 1mL of sample onto center of bottom film.

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Environmental Monitoring Procedures**

Select swab containing appropriate neutralizer. Hold the swab handle to make a 30° angle with the surface. Firmly rub the swab head slowly and thoroughly over the desired surface area. Rub the head of the swab three times over the surface, reversing direction between alternating strokes.

1 After sampling is complete, securely insert the swab head back into the swab tube and transport to the lab for plating. Plate the swab solution as soon as possible.

2

Release top film; allow it to drop. DO NOT roll top film down.

5

Release top film; allow it to drop. DO NOT roll top film down.

7

With ridge side down, place plastic spreader over inoculum. Gently apply pressure to evenly distribute sample.

6

With ridge side down, place plastic spreader over inoculum. Gently apply pressure to evenly distribute sample.

8

Incubate 3M™ Petrifilm™ AC Plates and inspect plates.

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Incubate 3M™ Petrifilm™ AC Plates and inspect plates.

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* 3M Food Safety does not operate or control products or services offered by third parties such as Laboratory Media Corporation, and cannot provide support for them. Laboratory Media Corporation is responsible for all aspects of order processing, fulfillment, billing and customer service. 3M Food Safety is not a party to the transactions entered into between customers and Laboratory Media Corporation. Any use of or purchase from Laboratory Media Corporation or other liquid or powdered media supplier is at the sole risk of the customer and is without warranties of any kind by 3M Food Safety, express, implied or otherwise, including warranties of merchantability or fitness for purpose.

3M and Petrifilm are trademarks of 3M. Used under license in Canada. Please recycle. Printed in U.S.A. © 3M 2011. All rights reserved. 70-2009-9489-8 (91.1)ii

3M CanadaPost Office Box 5757London, Ontario N6A 4T1Canada1-800-364-3577

3M Food Safety3M Center Building 275-5W-05St. Paul, MN 55144-1000USA1-800-328-6553www.3M.com/foodsafety

3M Food Safety offers a full line of products to accomplish a variety of your microbial testing needs. For more product information, visit us at www.3M.com/foodsafety.

Order Information 3M™ Petrifilm™ PlatesProduct Catalog Number Quantity

3M™ Petrifilm™ Aerobic Count Plates (AC)6400 100 plates/box

6406 1000 plates/case

To order, call 3M Food Safety Customer Service at 1-800-328-1671 or contact your local 3M representative.

Prepare Your Own Broth*Prepare Aerobic Lactic Acid Bacteria Broth by combining MRS (deMan, Rogosa and Sharpe) powdered media at twice label instructions with 42mg Chlorophenol Red (sodium salt, CAS Registry Number 123333-64-2) per 100mL broth. Autoclave or sterile filter. Store at 4–8°C.

Important Note: The user must ensure that the performance of Lactic Acid Bacteria Broth from any other source, including broth prepared by the user, meets the user’s needs.

Purchase Pre-made Broth* Product Catalog Number Quantity

Aerobic Lactic Acid Bacteria Broth LM406 10 – 25mL vials/case

To order, call Laboratory Media Corporation at 1-630-897-8000 or fax to 1-630-897-7990 or email labmedia@aol.com.