an epidemiological study of listeriosis in dairy cattle

and 0.94 for L. monocytogenes (17/18). The results are shown in the Table 5. 2. On the
basis of these results it was decided to culture faecal samples immediately after
collection, then after 3 and 7 weeks of cold enrichment.
Table 5. 2. Effect of cold enrichment on the growth quantity of Listeria spp.
weeks of cold enrichment
N = 20 0 1 2 3* 4 5 6 7* 13 14 15
Listeria spp 0 4 9 13 13 12 14 17 15 16 15
(%)
(20) (45) (65) (65) (60) (85) (85) (75) (80) (75)
Sensitivity 0 0.22 0.5 0.72 0.72 0.67 0.78 0.94 0.83 0.89 0.83
monocytogenes 0 4 7 10 10 6 10 11 11 12 13
(%)
(20) (35) (50) (50) (30) (50) (55) (55) (60) (65)
Sensitivity 0 0.22 0.39 0.56 0.56 0.33 0.56 0.61 0.61 0.67 0.72
( ) percentage, 0 cultured when fresh,* high sensitivity and number of isolates, N number of samples
examined
The effect of different storage media during cold enrichment: Saline had an adverse
affect on the growth quantity of Listeria after cold enrichment when compared with
those kept with no media (Table 5. 3.) but this effect was not statistically significant
(P=0.7 for first culture, P=1 for second culture).
Table 5. 3. Effect of saline the isolation of Listeria.
Listeria spp
Culture
Samples in no media Samples in saline
N=20 (%)
N=20 (%)
1 14 (70) 12 (60)
2
N number of samples tested
16 (80) 15 (75)
LSEB and NB were used to increase the chance of obtaining the maximum
number of isolates of L. monocytogenes. 79 samples (collected in March) were used in
this study. Culture was carried out weekly for the first 3 weeks then after 7 weeks of
cold enrichment. Although an increase in number of isolates was observed after the 1st
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