TABLE 4.
Comparison of detection of Y. pseudotuberculosis in 25-g portions of natural food samples by using real-time PCR following enrichment and DNA extraction and by culture methoda
| Sample no. | Sample type | CT Ypd | CT IPCd | PCR | Culture |
|---|---|---|---|---|---|
| 1 | Grated carrotsb,c | 39.58 | + | − | |
| 2 | Grated carrotsb,c | 36.68 | + | − | |
| 3 | Grated carrots and Swedish turnip saladb,c | 38.85 | + | − | |
| 4 | Grated Chinese cabbage, carrots, and cabbage saladb,c | 32.81 | − | − | |
| 5 | Carrots in cubesb,c | 34.63 | − | − | |
| 6 | Carrotsb,c | 39.66 | − | − | |
| 7-15 | Iceberg lettuce | 31.45-33.70 | − | − | |
| 16 | Mixed iceberg lettuce and red lettuce | 31.49 | − | − | |
| 17 | Grated carrots | 31.85 | − | − | |
| 18 | Pumpkin | 33.42 | − | − | |
| 19 | Grated carrots | 34.32 | − | − | |
| 20 | Chinese cabbage | 33.35 | − | − | |
| 21 | Tomatoes in cubes | 33.15 | − | − | |
| 22 | Grated cabbage | 33.33 | − | − | |
| 23 | Grated carrots and onionsb | 39.03 | + | − | |
| 24 | Grated carrots and onionsb | 37.98 | + | − | |
| 25 | Carrotsb | 33.11 | + | − |
DNA extraction was performed by using the MasterPure complete DNA purification kit (Epicentre Biotechnologies, Madison, WI). The culture method was performed by using cold enrichment at 4°C in phosphate-buffered saline broth supplemented with 1% mannitol and 0.15% bile salts for 14 days (14). Extracted DNA was diluted prior to PCR run by 1/10 for samples 7-24 and 1/80 for samples 6 and 25.
Samples related to outbreak investigations.
Samples were cultured in 2006, after which point they were stored in the freezer and reanalyzed by PCR in 2008 (starting with enrichment in TSBY for 24 h).
IPC, internal positive control. CT values are mean of two replicates.