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B
ird
et al
.:
J
ournal of
AOAC I
nternational
V
ol
.
99, N
o
.
3, 2016
FOOD BIOLOGICAL CONTAMINANTS
Evaluation of the 3M™ Petrifilm™ Rapid Aerobic Count Plate
for the Enumeration of Aerobic Bacteria: Collaborative Study,
First Action 2015.13
P
atrick
B
ird
, J
onathan
F
lannery
, E
rin
C
rowley
, J
ames
A
gin
,
and
D
avid
G
oins
Q Laboratories, Inc., 1400 Harrison Ave, Cincinnati, OH 45214
R
obert
J
echorek
3M Food Safety Department, 3M Center, Bldg 260-6B-01, St. Paul, MN 55144
Collaborators: K. Angeles, K. Beers, B. Brahmanda, A. Brandt, R. Brooks, B. Brown, N. Cuthbert, C. Fagundes, K. Gonzales, A. Hankins,
L. Hardrath, B. Kupski, C. Lopez, J. Marchant-Tambone, A. Mastalerz, W. McMahon, J. Meyer, K. Miller, A. Morris, K. Payne-McDaniel, J. Pickett,
J. Reynolds, R. Rodgers, J. Schoeni, L. Thompson, H. Wright
The 3M™ Petrifilm™ Rapid Aerobic Count (RAC) Plate
is a sample-ready culture medium system containing
dual-sensor indicator technology for the rapid
quantification of aerobic bacteria in food products.
The 3M Petrifilm RAC Plate was compared to the
U.S. Food and Drug Administration
Bacteriological
Analytical Manual
(FDA BAM) Chapter 3 (Aerobic
Plate Count) for the enumeration of aerobic bacteria
in raw easy-peel shrimp and the
Standard Methods
for the Examination of Dairy Products
(SMEDP)
Chapter 6 (Standard Plate Count Method) for the
enumeration of aerobic bacteria in pasteurized
skim milk and instant nonfat dry milk (instant
NFDM). The 3M Petrifilm RAC Plate was evaluated
using a paired study design in a multilaboratory
collaborative study following current AOAC validation
guidelines. Three target contamination levels (low,
10–100 CFU/g; medium, 100–1000 CFU/g; and high
1000–10 000 CFU/g) were evaluated for naturally
occurring aerobic microflora for each matrix. For raw
easy-peel shrimp, duplicate 3M Petrifilm RAC Plates
were enumerated after 24 ± 2 h incubation at both
32 and 35°C. Pasteurized skim milk 3M Petrifilm RAC
Plates were enumerated after 24 ± 2 h incubation
at 32°C, and instant NFDM 3M Petrifilm RAC Plates
were enumerated after 48 ± 3 h incubation at 32°C.
No statistical difference was observed between
3M Petrifilm RAC Plate and FDA BAM or SMEDP
reference methods for each contamination level.
A
erobic plate counts are often used in the food industry
to gauge the sanitary quality of food commodities
throughout the production process, starting from raw
materials used as ingredients to the shelf-life stability of finished
products (1). Although generally not used as a safety indicator
in food products, aerobic plate count can be useful in providing
information on the deficiencies in sanitation systems or flaws in
process control systems (2).This test can alsobe useful inproviding
information on the sanitary conditions of storage and processing
facilities (1). Cultural enumeration of aerobic microflora can take
48–72 h, depending on the matrix, and can produce wide-ranging
results as a result of difficulties that arise in the discernment of
bacterial counts from matrix particulate. The 3M™ Petrifilm™
Rapid Aerobic Count (RAC) Plate uses a cold-water-soluble
gelling agent and dual-sensing indicator technology to facilitate
the enumeration of aerobic bacteria after 24 h of incubation for
most foods (48 h for dairy powders, including whey powders).
The 3M Petrifilm RAC Plate allows for the simple and rapid
enumerationof aerobic bacteria in the food andbeverage industries.
Samples are diluted in Butterfield’s phosphate diluent (BPD) and
a sample aliquot is plated onto the 3M Petrifilm RAC Plate. The
sample aliquot is dispersed throughout the growth area and the
plates can be incubated at either 32 or 35°C, depending on the
matrix. Enumeration of colonies can occur in as little as 24 h of
incubation for most matrixes. Enumeration is made easier due
to the indicators in the gelling agent that use color to distinguish
bacterial colonies from food particles.
Prior to the collaborative study, the 3M Petrifilm RAC Plate
was validated according to AOAC validation guidelines (3) in
a harmonized AOAC
Performance Tested Method
SM
(PTM)
study. The objective of the PTM study was to demonstrate that
the 3M Petrifilm RAC Plate accurately enumerated aerobic
bacteria in select foods as claimed by the manufacturer and
that no difference in repeatability was observed between the
3M Petrifilm RAC Plate method and the reference methods.
For the 3M Petrifilm RAC Plate PTM evaluation, 16 matrixes
were evaluated: raw ground beef, raw ground pork, raw
ground turkey, chicken carcass rinsate, fresh swai, fresh tuna,
fresh tiger shrimp, raw easy-peel shrimp, cherry tomato wash,
frozen blueberries, dried Mediterranean apricots, creamy salad
dressing, fresh pasta, vanilla ice cream, instant nonfat dry milk
(NFDM), and pasteurized skim milk.
Submitted for publication January 6, 2016.
Corresponding author’s email:
pbird@qlaboratories.comThis method was approved by the Expert Review Panel for
Microbiology Methods for Food and Environmental Surfaces as First
Action.
The Expert Review Panel for Microbiology Methods for Food and
Environmental Surfaces invites method users to provide feedback on
the First Action methods. Feedback from method users will help verify
that the methods are fit-for-purpose and are critical for gaining global
recognition and acceptance of the methods. Comments can be sent
directly to the corresponding author or
methodfeedback@aoac.org.DOI: 10.5740/jaoacint.15-0260