3M Petrifilm™ Staph Express Count Plates Instruction

Interpretation
Guide
The 3M™ Petrifilm™ Staph Express System
consists of a 3M™ Petrifilm™ Staph Express
Count Plate and a 3M™ Petrifilm™ Staph
Express Disk, which are packaged separately.
The 3M Petrifilm Staph Express System is
used for the enumeration of DNase positive
Staphylococcus species in the food and
beverage industries.
STX
Staph Express System
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3M™ Petrifilm™ Staph Express Count Plate
The 3M™ Petrifilm™ Staph Express Count Plate is a
sample-ready-culture medium system which contains
a cold-water-soluble gelling agent. The chromogenic,
modified Baird-Parker medium in the plate is selective
and differential for Staphylococcus aureus (S. aureus)
but may also indicate Staphylococcus hyicus (S. hyicus)
or Staphylococcus intermedius (S. intermedius).
Red-violet colonies are S. aureus, S. hyicus or S.
intermedius. If you encounter background flora in your
testing, the 3M™ Petrifilm™ Staph Express Disk may be
used to identify S. aureus from all suspect colonies.
S. aureus count = 11
This picture shows only red-violet colonies. Count all red-violet
colonies as S. aureus. The test is complete.
3M™ Petrifilm™ Staph Express Disk
The 3M Petrifilm Staph Express Disk should be used
whenever colonies other than red-violet are present on
the plate —for example, black or blue-green colonies—
as they may obscure S. aureus. Black colonies may or
may not be S. aureus. Blue-green colonies are not S.
aureus.
The 3M Petrifilm Staph Express Disk contains
toludine blue-O and deoxyribonucleic acid (DNA).
Deoxyribonuclease (DNase) positive organisms degrade
the DNA which reacts with the toludine blue-O to
form pink zones. DNase positive organisms include S.
aureus, S. hyicus, and S. intermedius and comprise the
majority of the group of organisms commonly known as
coagulase-positive staphylococci. Most other types of
bacteria do not produce pink zones.
S. aureus count = 33
Staph Express System
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Figure 1
Figure 2
S. aureus count = 0
S. aureus count = 24
This 3M Petrifilm Staph Express Count Plate has no colonies
after 24 hours of incubation. The test is complete.
S. aureus colonies may vary in size. Count all red-violet colonies
regardless of size. Use an illuminated magnifier so that the
colonies are easier to see. The test is complete.
Figure 3
Figure 4
S. aureus count = 122
S. aureus count = TNTC
The recommended counting limit on a 3M Petrifilm
Staph Express Count Plate is 150 S. aureus colonies. The
plate in Figure 3 is approaching the counting limit. The
test is complete as there are only red-violet colonies
present on the plate.
When the number of S. aureus colonies exceeds 150, the colonies
become too numerous to count (TNTC). Estimate the count or dilute
your sample further. To estimate the count, count the colonies in one
representative square and multiply that number by 30.
For a more accurate count, further dilution of the sample may be
necessary.
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Figure 5a
Figure 5b
Figure 6a
Figure 6b
S. aureus count = 7
S. aureus count = 17
Food particles in this figure are irregularly shaped. S. aureus is
easier to enumerate once the disk has been inserted because the
zones are more clearly distinguished from the food.
Count pink zones as S. aureus, regardless of the size of the
zone. The arrows in Figure 6b show gel splitting. Gel splitting
does not affect the performance.
Figure 7a
Figure 7b
S. aureus count = 3
Individual colonies are difficult to see due to food and/or large
numbers of background bacteria as depicted by discoloration
of the plate in Figure 7a. Insert the disk and count pink zones as
S. aureus.
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Reminders for Use
Storage
Inoculation
1 mL
≤8°C
1
Store unopened 3M Petrifilm Staph
Express Count Plates and 3M Petrifilm
Staph Express Disks frozen or refrigerated
temperatures ≤8°C (46°F). Just prior to
use, allow unopened pouches to come to
room temperature before opening. Return
unused plates to pouch.
2
Seal by folding the end of the pouch
over and applying adhesive tape. To
prevent exposure to moisture, do not
refrigerate opened pouches. Store
resealed pouches in a cool dry place. Use
plates within four weeks. Use disks within
six months.
3
Place the 3M Petrifilm Staph Express
Count Plates on a flat, level surface. Lift the
top film and with the pipette perpendicular
dispense 1 mL of sample suspension onto
the center of bottom film.
Incubation
4
Roll the top film down onto the sample to
prevent trapping air bubbles.
5
Place the 3M™ Petrifilm™ Flat
Spreader with the flat side down on the
center of the plate. Press gently on the
center of the spreader to distribute the
inoculum over the circular area. Do not
twist or side the spreader. Remove the
spreader and leave the 3M Petrifilm
Staph Express Plate undisturbed for
at least one minute to permit the gel
to form.
6
Incubate 3M Petrifilm Staph Express
Plates with the clear side up in stacks of
no more than 20 plates. Please refer to
the the product instructions for third
party validated methods.
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Lift the top film of the 3M Petrifilm Staph
Express Count Plate and place the 3M
Petrifilm Staph Express Disk in the well of
the plate so that the tab remains outside
the well. Apply gentle pressure to the
disk area.
9
Incubate plates with inserted disks in
stacks of no more than 20 plates. Please
refer to the product instructions for third
party validated methods.
Interpretation
7
Count 3M Petrifilm Staph Express Plates
with a standard colony counter or other
illuminated magnifier. Do not count
colonies on the foam dam since they are
removed from the selective influence of
the medium.
Staph Express System
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Use Appropiate Sterile Diluents
Butterfield’s phosphate buffered dilution water, peptone salt diluent, 0.1% peptone
water, buffered peptone water, quarter-strength Ringer’s solution, saline solution
(0.85-0.90%), bisulfite-free letheen broth, or distilled water.
For optimal growth and recovery of the microorganisms, adjust the pH of the sample
suspension to 6-8.
Do not use diluents containing citrate, bisulfite, or thiosulfate; they can inhibit growth.
Do not use dipotassium hydrogen phosphate as the DNase reaction may be inhibited.
10
Count all pink zones whether or not a
colony is visible.
Select commercially made buffered peptone water media formulated to meet the
requirements of ISO 6887 (buffered peptone water (BPW (ISO)) may inhibit the DNase
reaction resulting in no pink zone formation when the 3M Petrifilm Staph Express
Count Plate is used with the 3M Petrifilm Staph Express Disk. It is important to verify
the performance of the 3M Petrifilm Staph Express Disk with the diluent chosen for
sample preparation. Failure to do so, may result in false negatives.
If citrate buffer is indicated in the standard procedure, substitute warmed to 40-45ºC
(104-113°F) Butterfield’s phosphate buffered dilution water or peptone salt diluent.
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 3M.com/foodsafety/Petrifilm
or call 1-800-328-6553.
User’s Responsibilities: 3M Petrifilm Plate performance has not been evaluated with all combinations
of microbial flora, incubation conditions and food matrices. It is the user’s responsibility to determine
that any test methods and results meet the user’s requirements. Should re-printing of this Interpretation
Guide be necessary, user’s print settings may impact picture and color quality.
3M Food Safety
3M Center, Building 275-5W-05
St. Paul, MN 55144-1000 USA
1-800-328-6553
3M.com/foodsafety
3M Canada
Post Office Box 5757
London, Ontario N6A 4T1
Canada
1-800-364-3577
Staph Express System
For detailed CAUTIONS, DISCLAIMER OF WARRANTIES/LIMITED REMEDY
and LIMITATION OF 3M LIABILITY, STORAGE AND DISPOSAL information
and INSTRUCTIONS FOR USE, see Product’s package insert.
3M and Petrifilm are trademarks of 3M. Used under license in Canada.
Please recycle. Printed in USA. © 3M 2017. All rights reserved.
70-2009-4286-3 (Rev-1217)
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