Table 3.
Comparison of sensitivities and quantitative capabilities of LAMP, PCR, and qPCR assays alone or in combination with PMA when testing serially diluted Salmonella enterica serovar Typhimurium LT2 viable cells in pure culture and spiked produce samples
| Sample typea | Methodb | Produce type | Detection limit (CFU/reaction or CFU/g) | Quantification equationg | Linear R2g |
|---|---|---|---|---|---|
| Pure culture | LAMP | NAh | 1.3–13c | y = −0.85x + 24.82 | 0.983 |
| PCR | NA | 130 | NA | NA | |
| qPCR | NA | 1.3 | y = −1.82x + 32.72 | 0.997 | |
| PMA-LAMP | NA | 3.4–34d | y = −2.06x + 29.58 | 0.970 | |
| PMA-PCR | NA | 340 | NA | NA | |
| PMA-qPCR | NA | 3.4–34e | y = −3.04x + 36.95 | 0.997 | |
| Spiked produce | PMA-LAMP | Cantaloupe | 6.1 × 103 | y = −2.51x + 39.39 | 0.993 |
| Spinach | 6.1 × 104 | y = −4.63x + 55.47 | 0.977 | ||
| Tomato | 6.1 × 104 | y = −1.78x + 36.57 | 0.949 | ||
| PMA-PCR | Cantaloupe | 6.1 × 105 | NA | NA | |
| Spinach | 6.1 × 105 | NA | NA | ||
| Tomato | 6.1 × 105 | NA | NA | ||
| PMA-qPCR | Cantaloupe | 6.1 × 103 | y = −3.54x + 46.06 | 0.998 | |
| Spinach | 6.1 × 102–6.1 × 103f | y = −3.50x + 46.08 | 0.993 | ||
| Tomato | 6.1 × 102 | y = −3.47x + 46.03 | 0.987 |
Four independent repeats were conducted for pure culture testing, and three repeats were conducted for spiked produce testing.
For testing involving PMA, dead Salmonella cells were present at a level of 3.8 × 103 CFU/reaction (or 2.1 × 105 CFU/g).
One out of four repeats was positive for the 1.3-CFU/reaction level.
One out of four repeats was positive for the 3.4-CFU/reaction level.
Three out of four repeats were positive for the 3.4-CFU/reaction level.
One out of two repeats was positive for the 6.1 × 102-CFU/g level.
Quantitative equation and R2 were calculated based on the linear relationship of average T T or C T values and log CFU/reaction between viable cell levels ranging from 102 to 105 CFU/reaction for pure culture and between 104 and 107 CFU/g for spiked produce samples.
NA, not applicable.