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B
ird
et al
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:
J
ournal of
AOAC I
nternational
V
ol
. 98, N
o
. 3, 2015
solidify in the 3M Petrifilm RYM Count Plate medium. Several
laboratories also indicated that the colonies were very easy to
interpret due to their size and color. One laboratory indicated
that the “Space saving benefits of Petrifilm over the traditional
FDA BAM method are readily apparent.”
During the analysis of samples, several laboratories indicated
deviating from the approved protocol and therefore, their
data was subsequently removed from statistical analysis. No
laboratories were removed from statistical analysis as a result
of their data. For the raw ground beef, four laboratories were
removed from statistical analysis. Laboratory 12 was unable to
enumerate samples by both the 3M Petrifilm RYM Count Plate
method and reference methods on the same day. All samples
were plated onto DRBC, then stored at 2–8°C overnight and
plated onto the Petrifilm RYM plates the following day.
Laboratories 6 and 8 prepared the reference method samples
using duplicate plating and not the required triplicate plating.
Laboratory 4 (for both raw ground beef and raw almonds) failed
to enumerate the 3M Petrifilm RYM Count Plates at the 60 h
time point. Due to these deviations, these laboratories were
removed from statistical analysis.
There were no statistically significant differences at the
5% level in log transformed means between the 3M Petrifilm
RYM Count Plate method and FDA BAM/ISO 21257 methods
for either matrix evaluated in this study, at any of the three
contamination levels. No statistically significant differences
were observed between the 3M Petrifilm RYM Count Plate
results when enumerated at 48 h versus 60 h and compared to
the FDA BAM/ISO 21527 methods. No statistically significant
differences were also observed between 3M Petrifilm RYM
Count Plates that were incubated at 25°C and 28°C when
compared to the FDA BAM/ISO 21527 methods. Based on
the data presented, the s
r
values obtained at all incubation
conditions and for all three contamination levels were generally
similar between the two methods.
For raw frozen ground beef patties and raw almonds, the 3M
Petrifilm RYM Count Plate method was more repeatable than
the FDA BAM/ISO 21527 reference methods for one of the
six contamination levels analyzed at 25°C and four of the six
contamination levels analyzed at 28°C.
Recommendations
It is recommended that the 3M Petrifilm Rapid Yeast and
Mold Count (RYM) Plate method be adopted as Official First
Action status for the enumeration of yeast and molds in the
following high water activity matrixes: yogurt (1.5% fat),
frozen bread dough, fermented salami, sour cream, ready-made
pie, raw frozen ground beef patties (77%), ready-to-eat deli
sandwiches, sliced apples, and the following low water activity
matrixes: raw almonds and dehydrated soup.
Acknowledgments
We would like to extend a sincere thank you to the following
collaborators for their dedicated participation in this study:
Dave Metzger, Wendy Lee, and Thomas Hirsch, Accelerated
Analytical, Milwaukee, WI
Peyman Fatemi and Sharon Spencer, Aemtek, Inc., Fremont,
CA
Joel Blumfield, EDL Labs, Inc., Purvis, MS
Bryan Dieckleman, Eurofins Microbiology Laboratories,
Inc., Des Moines, IA
Karilyn Gonzales and Chelsea Fagundes, Food
Microbiological Laboratories, Inc., Cypress, CA
Jerry Reed and Jeraldine Medellin, Metrix 360 Laboratories,
San Antonio, TX
Adam Hankins, McCoy and McCoy Laboratories, Inc.,
Madisonville, KY
Figure 1: 3M Petrifilm RYM Count Plate vs. FDA BAM/ISO 21527 Results for Frozen Raw
Ground Beef Patties Incubated at 25
o
C and Enumerated at 48 and 60 Hours
2.00
2.50
3.00
3.50
4.00
4.50
5.00
2.00
2.50
3.00
3.50
4.00
4.50
5.00
Log1 3M RYM CFU/g Results
Log10 FDA BAM/ISO 21527 CFU/g Results
3M Petrifilm RYM Count Plate vs. FDA BAM/ISO
21527 for Raw Ground Beef Incubated at 25
o
C
Frozen Raw Ground Beef Patties
25C Enumerated at 48 Hours
Frozen Raw Ground Beef Patties
25C Enumerated at 60 Hours
Figure 1. 3M Petrifilm RYM Count Plate versus FDA BAM/ISO
21527 results for frozen raw ground beef patties incubated at 25°C
and enumerated at 48 and 60 h.
Figure 2: 3M Petrifilm RYM Count Plate vs. FDA BAM/ISO 21527 Results for Frozen Raw
Ground Beef Patties Incubated at 28
o
C and Enumerated at 48 and 60 Hours
2
3
4
5
2
2.5
3
3.5
4
4.5
5
g
10
3M RYM CFU/g Results
Log
10
FDA BAM/ISO 21527 CFU/g Results
3M Petrifilm RYM Count Plate vs.
FDA BAM/ISO 21527 for Raw Ground Beef
Incubated at 28
o
C
Frozen Raw Ground Beef Patties
28C Enumerated at 48 Hours
Frozen Raw Ground Beef Patties
28C Enumerated at 60 Hours
Figure 2. 3M Petrifilm RYM Count Plate versus FDA BAM/ISO
21527 Results for frozen raw ground beef patties Incubated at 28
°
C
and Enumerated at 48 and 60 h.
Figure 3: 3M Petrifilm RYM Count Plate vs. FDA BAM/ISO 21527 Results for Raw Almonds
Incubated at 25
o
C and Enumerated at 48 and 60 Hours
2.00
2.50
3.00
3.50
4.00
4.50
5.00
2.00
2.50
3.00
3.50
Log1 3M RYM CFU/g Results
Log10 FDA BAM/ISO 21527 CFU/g Results
3M Petrifilm RYM Count Plate vs. FDA BAM/ISO
21527 for Raw Almonds Incubated at 25
o
C
Frozen Raw Almonds 25C
Enumerated at 48 Hours
Frozen Raw Almonds 25C
Enumerated at 60 Hours
Figure 3. 3M Petrifilm RYM Count Plate versus FDA BAM/ISO
21527 results for raw almonds incubated at 25
°
C and enumerated at
48 and 60 h.
Figure 4: 3M Petrifilm RYM Count Plate vs. FDA BAM/ISO 21527 Results for Raw Almonds
Incubated at 28
o
C and Enumerated at 48 and 60 Hours
2.00
3.00
4.00
5.00
2.00
2.50
3.00
3.50
Log
10
3M RYM CFU/g
Results
Log
10
FDA BAM/ISO 21527 CFU/g Results
3M Petrifilm RYM Count Plate vs. FDA BAM/ISO 21527 for Raw
Almonds Incubated at 28
o
C
Raw Ground Beef 28C Enumerated
at 48 Hours
Raw Ground Beef 28C Enumerated
at 60 Hours
Figure 4. 3M Petrifilm RYM Count Plate versus FDA BAM/ISO
21527 results for raw almonds incubated at 28
°
C and enumerated at
48 and 60 h.