The basis of the horizontal method for the Listeria monocytogenes detection in
milk and dairy is developing the strategies for improving the horizontal method of
Listeria monocytogenes detection in milk and dairy products with the help of research
suspension, prepared in the ratio of 1:5 (samples of milk and dairy products in the
amount of 10−11 cm
3
(d) and 50−55 cm
3
of initial selective enriched medium(half of
Fraser broth), and further incubation of the suspension for 21−23 hours at temperature
of 31±1 °C and secondary enrichment. After the first initial enrichment the received
culture in the amount of 0.05−0.06 cm
3
is transferred into the test tube that contains
5−6 cm
3
of second time enriched medium (Fraser broth). Then the environment with
crops is incubated for 46−48 hours at the temperature of 37 °C. After that the primary
(5−6 cm
3
) and the secondary (2,5−30 cm
3
) enriched culture in terms of selective
environment PALKAM-agaris in oculatedandis carried out to get clearly separated
colonies of Listeria monocytogenes for 24±2 hours at the temperature of 37±1 °C in
the form of small green grey or olive green colonies, 1.5–2 mm in diameter, sometimes
with a black halo, in 48 hours they are in the form of green colonies, 1.5–2 mm in
diameter with deeply sunk center and a black halo around.
Table 3 Indices of improved horizontal method of Listeria monocytogenes
detection in milk and dairy products on the basis of the third example
№
List of the studied samples of
milk and dairy products
Detection of Listeria monocytogenes according to the color
and size of colonies on the basis example number 3
The
quantity
of
samples
The presence of
colonies Listeria
monocytogenes
The
quantity
of
samples
The absence of
Listeria
monocytogenes
colonies
1
Raw Milk (fatcontent of 3.7
%), n=10
n=3
After 24 ± 2
hours a colony of
small (1.5−2,0
mm) green
grey or olive
green color,
sometimes with a
black halo.
In 46 ± 2 hours
(1.5−2,0 mm) of
green color with
deeply sunk
centre and a
blackhalo
n=8
Specific
colonie sof
Listeria
monocytogenes
аre not
detected
2
Pasteurized milk (contentoffat
2.8 %), n= 10
n=0
n=10
3
Cream, n=6
n=2
n=4
4
Pasteurized Cream, n=5
n=0
n=5
5
Cheese, n=6
n=2
n=4
6
Curd, n=7
n=1
n=6
7
Melted cheese, n=8
n=3
n=5
8
Butter, n=9
n=2
n=7
9
Spread, n=6
n=1
n=5
The results of our research showed that Listeria monocytogenes colonies were
found in 24±2 hours. They were of small size about 1.5–2.0 mm in diameter of grey-
green or olive-green color, sometimes with a black halo. In 46±2 hours they were of
green color with deeply sunk centre and a black halo in the following samples of milk
and dairy products (3 samples of raw milk and melted cheese; in 2 samples of cream,
- 1266 -