Table 1.
Detection of Salmonella enterica by invA qPCR, invA mRNA RT-qPCR, invA LAMP assays, and BAM in artificially contaminated produce after 24 h of enrichment
| Produce | Salmonella strain | Minimum inoculation level detected (CFU/25 g) | Positivity for presence of Salmonella spp. by: |
qPCR (Cq) DNA presenceb | Salmonella enrichment (cells/ml)c | |||
|---|---|---|---|---|---|---|---|---|
| qPCR (Cq)a | LAMP | RT-qPCR (Cq)a | BAM | |||||
| Cilantro | S. Enteritidis SARB18 | 2 | + (23.90 ± 0.42) | + | + (28.26 ± 0.40) | + | − | 8.23E7 |
| S. Newport 1240H | 3 | + (28.57 ± 0.30) | + | + (29.76 ± 0.82) | + | − | 3.77E6 | |
| S. Saintpaul 1358H | 10 | + (32.93 ± 1.17) | + | + (34.13 ± 0.36) | + | − | 2.17E5 | |
| S. Typhimurium SARA9 | 20 | + (24.24 ± 0.15) | + | + (26.85 ± 0.82) | + | − | 6.58E7 | |
| Lettuce | S. Enteritidis SARB18 | 2 | + (21.84 ± 0.16) | + | + (24.42 ± 0.42) | + | − | 3.20E8 |
| S. Newport 1240H | 14 | + (24.40 ± 0.75) | + | + (24.55 ± 0.41) | + | − | 5.92E7 | |
| S. Saintpaul 1358H | 1 | + (22.92 ± 0.32) | + | + (24.45 ± 0.02) | + | − | 1.57E8 | |
| S. Typhimurium SARA9 | 2 | + (27.18 ± 1.26) | + | + (24.79 ± 0.22) | + | − | 9.45E6 | |
| Parsley | S. Enteritidis SARB18 | 8 | + (21.62 ± 0.04) | + | + (30.16 ± 0.24) | + | − | 3.71E8 |
| S. Newport 1240H | 2 | + (24.57 ± 0.82) | + | + (32.96 ± 0.08) | + | − | 5.29E7 | |
| S. Saintpaul 1358H | 10 | + (24.33 ± 0.14) | + | + (26.30 ± 0.41) | + | − | 6.20E7 | |
| S. Typhimurium SARA9 | 2 | + (22.78 ± 0.05) | + | + (30.43 ± 0.63) | + | − | 1.72E8 | |
| Spinach | S. Enteritidis SARB18 | 1 | + (27.96 ± 0.16) | + | + (28.96 ± 1.08) | + | − | 5.65E6 |
| S. Newport 1240H | 10 | + (29.75 ± 1.07) | + | + (28.12 ± 0.39) | + | − | 1.73E6 | |
| S. Saintpaul 1358H | 1 | + (28.85 ± 0.15) | + | + (24.43 ± 0.15) | + | − | 3.14E6 | |
| S. Typhimurium SARA9 | 1 | + (24.73 ± 0.06) | + | + (22.60 ± 0.34) | + | − | 4.76E7 | |
| Tomato (round) | S. Enteritidis SARB18 | 19 | + (18.06 ± 0.10) | + | + (27.70 ± 0.12) | + | + (34.36) | 3.88E9 |
| S. Newport 1240H | 15 | + (19.27 ± 0.32) | + | + (23.30 ± 0.11) | + | − | 1.75E9 | |
| S. Saintpaul 1358H | 2 | + (17.10 ± 0.14) | + | + (25.35 ± 0.41) | + | − | 7.32E9 | |
| S. Typhimurium SARA9 | 15 | + (19.36 ± 0.08) | + | + (25.04 ± 0.30) | + | − | 1.65E9 | |
| Jalapeno pepper | S. Enteritidis SARB18 | 2 | + (26.16 ± 0.59) | + | + (25.75 ± 1.86) | + | − | 1.85E7 |
| S. Newport 1240H | 2 | + (28.33 ± 0.40) | + | + (30.51 ± 0.10) | + | − | 4.51E6 | |
| S. Saintpaul 1358H | 2 | + (24.10 ± 0.15) | + | + (33.60 ± 0.21) | + | − | 7.21E7 | |
| S. Typhimurium SARA9 | 2 | + (21.38 ± 0.13) | + | + (20.58 ± 0.46) | + | + (34.40) | 4.34E8 | |
a
Cq, cycle threshold was set at 1,000 fluorescent units (FU, dR) in a Stratagene Mx3005P real-time PCR machine. Cq values are given in parentheses. +, Salmonella positive by the method. −, Salmonella negative by the method.
b
Same RNA samples amplified by qPCR to test for DNA contamination.
c
The number of Salmonella cells/ml was assumed to be equivalent to the number of invA copies/ml of enrichment as calculated by qPCR.