CompactDry SL
4817
NISSUI ready-to-use, sterile
Ready-made plates with anhydrous chromogenic
nutrient medium for detection of samonellae
A. Introduction
Compact Dry plates made by NISSUI are suitable for
detection and enumeration of microorganisms from
foods and feeds, cosmetics and pharmaceutical
samples, as well as for hygiene monitoring and
contamination control in food-producing areas. Due to
the chromogenic additives, bacterial colonies depict
specific colouring, making them easy to interpret.
The nutrient medium used for Compact Dry SL plates is
deduced from the formulation of Triple Sugar Iron Agar.
Salmonellae may easily be identified by the green
colouring of the colonies, accompanied by colour shift of
the plate to yellow due to alcalization of the medium.
Salmonellae producing hydrogen sulphide grow in black
colonies on yellow medium.
B. Storage and Usage
CompactDry plates are stabile at room temperature and
at 4 °C. Store protected from moisture and light.
Do not use the product after its expiry date. Quality of
the product is not warranted after being expired. Do not
use the product that contains any foreign materials,
discoloured or dehydrated, or its container is damaged.
After opening the aluminum bag, any plates unused
should be put back into the aluminum bag to be sealed
with tape to avoid light and moisture, and use up as
soon as possible.
C. Sample preparation
From waters or liquid foods
Add 9 times volume of Buffered Peptone Water to 1 vol.
liquid specimen. Filtrate the liquid sample through
membrane filter, and put the filter into Buffered Peptone
Water.
From solid foods
Take 25 g of solid specimen into the sterilized
homogenizer bag. Add 225 ml of sterile Buffered
Peptone Water into the bag, and homogenize for about
one (1) minute
From surfaces
Wir recommend using the CompactDry Swab (Art. No.
225K). Use the swab to wipe the surface, put into the
device with wiping solution. Add 9 ml of Buffered
Peptone Water to 1 ml of this solution.
D. Application
1. Incubate the samples in the closed homogenizer
bag for 20-24 hours at 35-37 °C in the incubator for
preenrichment.
2. Rub the bag for homogenization.
3. Open the plate and gently drop 0.1 ml (3 drops) of
enriched specimen onto the dry sheet (approx. 1 cm far
from the edge of plate). This enriched culture will stay at
dropped point. Diffusion of this dropped specimen shall
not reach to the edge of plate.
4. Gently drop 1 ml of sterilized water at the opposite
point where the specimen dropped. The water diffuses
automatically and evenly into the sheet and transforms
the dried sheet into a gel within seconds.
5. Put the cap back onto the plate and note date and
sample on the memorandum section.
6. Turn over the capped plate and incubate at
appropriate temperature.
7. After incubation count the number of coloured
colonies underneath the plate. White paper placed
under the plate helps with counting.
Incubation:
Please use the incubation time/temperature according
to the national food analysis recommended for total
viable count.
General recommendation: 42 °C for 24 hours
E. Interpretation
Salmonella Positive
1.) Black to green isolated or fused colonies.
2.) Colour of sheet around the colonies is changed to
yellow.
3.) Colonies have wandered all over the plate (motility).
In case of all three parameters are positive, consider
sample as Salmonella contaminated.
If a large quantity of Salmonella is present, no isolated
colonies are formed Rather there may be several spots
with fused black or green colonies, and whole plate
sheet becomes yellow.
Putative Salmonella positive or negative colonies have
to be confirmed by microbiological identification and
confirmation tests.
Salmonella Negative
There is no colour with the medium. If it occurs, the
sheet colour would change to red or reddish purple due
to fermentation of lactose or sucrose by coliforms. No
black or green colonies are observed.
Please note: The sheet colour might change to yellow
caused by large colony numbers of Pseudomonas or
Proteus. But yellow portion is small and limited because
of their less motility. Other Gram-negative bacteria are
inhibited in growth or don’t show any colour shift.
F. General comments
• Some colonies may be only weakly coloured. Since
false-negative results have to be avoided, those
colonies have to be counted as positives.
• Make sure CompactDry plates are well closed during
incubation, in order to avoid drying.
• High concentrations on plates will cause the entire
growth area to become red/pink. In this case dilute
the sample.
• After use please follow the current disposal
regulations.
• The growth area is 20 cm². The back of the plate has
a grid carved of 1 x 1 cm to make the colony counting
easier. In case of any difficulties to count colonies due
to large number of colonies grown, total viable count
can be obtained by multiplying 20 by an average
number of colonies per grid counted from several
grids.