Table 1.
Serotypes and genetic determinants of virulence of Listeria monocytogenes isolates.
| Food type | N | No. of positive samples (%) | No. of isolates | Serotype No. of isolates (%) | Genetic determinants of virulence No. of isolates (%) | |||||
|---|---|---|---|---|---|---|---|---|---|---|
| 1/2a | 1/2b | 1/2c | 4b | NT | LIPI-1* | LIPI-1 +inlAB | ||||
| Raw meat | 85 | 21 (25) | 21 | 8 (38) | 1 (5) | 3 (14)a(+) | 4 (19)b(−) | 5 (24)c(+) | 7 (33) | 7 (33) |
| Raw poultry | 85 | 10 (12) | 10 | 6 (60) | 2 (20) | 1 (10) | 1 (10) a(−) | 0 | 2 (20) a(−) | 2 (20) |
| Cooked sausage | 41 | 5 (13) | 5 | 1 (20) | 4 (80)c(+) | 0 | 0 | 0 | 1 (20) | 1 (20) |
| Frozen seafood | 197 | 50 (25) | 38 | 10 (26) | 3 (8) | 0 | 25(66)a(+) | 0 | 23 (60) | 23 (60) |
| Pâté | 62 | 34 (55) | 32 | 20 (62)c(+) | 3 (9) | 1 (3) | 4 (13)c(−) | 4 (13) | 5 (15)c(−) | 5 (15)c(−) |
| Smoked fish | 69 | 18 (26) | 16 | 5 (31) | 7 (44)c(+) | 0 | 3 (19)a(−) | 1 (6) | 14 (88)b(+) | 14 (88)b(+) |
| Cheese | 116 | 46 (40) | 46 | 0 | 0 | 0 | 46 (100) | 0 | 41 (89)c(+) | 32 (70)c(+) |
| Frozen vegetables | 90 | 26 (29) | 25 | 12 (48) | 3 (12) | 2 (8) | 8 (32) | 0 | 10 (40) | 9 (36) |
| Fresh vegetables | 105 | 2 (2) | 2 | 0 | 2 (100) | 0 | 0 | 0 | 0 | 0 |
| Total | 850 | 212 (25) | 195 | 62 (32) | 25 (13) | 7 (4) | 91 (46) | 10 (5) | 103 (53) | 93 (48) |
| Clinical isolates | 40 | 9 (23) | 10 (25) | 0 | 21 (52) | 0 | 26 (65) | 24 (60) | ||
N, Number of samples analyzed; NT, Not typeable.
*
Positive isolates of all genes present in the Listeria pathogenicity island 1 (LIPI-1), i.e., prfA, plcA, hly, mpl, actA, and plcB.
(−)
Prevalence significantly lower compared to all other food isolates.
(+)
Prevalence significantly higher compared to all other food isolates.
a, b, c
P-value for the association between the specific food vs. all other food isolates and the specified serotype/genetic determinant of virulence vs. all other serotypes/genetic determinants of virulence (aP < 0.05; bP < 0.01; cP < 0.001).
The underlined values means that only serotype isolated in respective food category.