Table 1.
Detection of Listeria in naturally contaminated samples using 3M™ MDA, 3M™ petrifilm environmental Listeria plate and EN ISO 11290-1 methods
| Samples | Number of samples/number of total samples (%) | ||||||
|---|---|---|---|---|---|---|---|
| EN ISO 11290-1 | 3M™ MDA | 3M™ petrifilm EL plate | |||||
| Positive | True positive | False positive | False negative | True positive | False positive | False negative | |
| Chicken samples | |||||||
| Chicken cuts | 1/10 (10.0) | 1/10 (10.0) | 0/10 (0) | 0/10 (0) | 1/10 (10) | 0/10 (0) | 0/10 (0) |
| Whole chicken | 2/9 (22.2) | 2/9 (22.2) | 0/9 (0) | 0/9 (0) | 2/9 (22.2) | 0/9 (0) | 0/9 (0) |
| Environmental samples | |||||||
| Display table | 2/11 (18.2) | 1/11 (9.10) | 0/11 (0) | 1/11 (9.10) | 1/11(9.10) | 0/11 (0) | 1/11 (9.10) |
| Chopping board | 3/9 (33.3) | 2/9 (22.2) | 0/9 (0) | 1/9 (11.1) | 3/9 (33.3) | 0/9 (0) | 0/9 (0) |
| Wash water | 2/9 (22.2) | 2/9 (22.2) | 0/9 (0) | 0/9 (0) | 2/9 (22.2) | 0/9 (0) | 0/9 (0) |
| Drain water | 4/9 (44.4) | 4/9 (44.4) | 0/9 (0) | 0/9 (0) | 3/9 (33.3) | 0/9 (0) | 1/9 (11.1) |
| Butcher apron | 2/8 (25.0) | 2/8 (25.0) | 0/8 (0) | 0/8 (0) | 2/8 (25.0) | 0/8 (0) | 0/8 (0) |
| Knife | 2/8 (25.0) | 2/8 (25.0) | 0/8 (0) | 0/8 (0) | 1/8 (12.5) | 0/8 (0) | 1/8 (12.5) |
| Transport crate | 2/8 (25.0) | 2/8 (25.0) | 0/8 (0) | 0/8 (0) | 2/8 (25.0) | 0/8 (0) | 0/8 (0) |
| Floor | 4/7 (57.1) | 4/7 (71.4) | 1/7 (14.2) | 0/7 (0) | 4/7 (57.1) | 0/7 (0) | 0/7 (0) |
| Scalding tank | 1/7 (14.2) | 1/7 (14.2) | 0/7 (0) | 0/7 (0) | 1/7 (14.2) | 0/7 (0) | 0/7 (0) |
| Defeathering machine | 1/7 (14.2) | 1/7 (14.2) | 0/7 (0) | 0/7 (0) | 1/7 (14.2) | 0/7 (0) | 0/7 (0) |
| Cage | 0/7 (0) | 0/7 (0) | 0/7 (0) | 0/7 (0) | 0/7 (0) | 0/7 (0) | 0/7 (0) |
| Drain crevices | 0/6 (0) | 0/6 (0) | 0/6 (0) | 0/6 (0) | 0/6 (0) | 0/6 (0) | 0/6 (0) |
| Bench wash water | 0/6 (0) | 0/6 (0) | 0/6 (0) | 0/6 (0) | 0/6 (0) | 0/6 (0) | 0/6 (0) |
| Drum | 0/5 (0) | 0/5 (0) | 0/5 (0) | 0/5 (0) | 0/5 (0) | 0/5 (0) | 0/5 (0) |
| Vegetables samples | |||||||
| Amaranth green | 2/4 (50.0) | 2/4 (50.0) | 0/4 (0) | 0/4 (0) | 2/4 (50.0) | 0/4 (0) | 0/4 (0) |
| Winged bean | 2/4 (50.0) | 2/4 (50.0) | 0/4 (0) | 0/4 (0) | 2/4 (50.0) | 0/4 (0) | 0/4 (0) |
| Laksa leaves | 1/4 (25.0) | 0/4 (0) | 0/4 (0) | 1/4 (25.0) | 0/4 (0) | 0/4 (0) | 1/4 (25.0) |
| Wild parsley | 1/4 (25.0) | 1/4 (25.0) | 0/4 (0) | 0/4 (0) | 1/4 (25.0) | 0/4 (0) | 0/4 (0) |
| Amaranth red | 1/3 (33.3) | 1/3 (33.3) | 0/3 (0) | 0/3 (0) | 1/3 (33.3) | 0/3 (0) | 0/3 (0) |
| Coriander | 2/3 (66.7) | 2/3 (66.6) | 0/3 (0) | 0/3 (0) | 2/3 (66.7) | 0/3 (0) | 0/3 (0) |
| Water spinach | 2/3 (66.7) | 2/3 (66.6) | 0/3 (0) | 0/3 (0) | 0/3 (0) | 0/3 (0) | 2/3 (66.7) |
| Iceberg lettuce | 1/3 (33.3) | 0/3 (0) | 0/3 (0) | 1/3 (33.3) | 0/3 (0) | 0/3 (0) | 1/3 (33.3) |
| Spring onion | 2/3 (66.7) | 2/3 (66.6) | 0/3 (0) | 0/3 (0) | 2/3 (66.6) | 0/3 (0) | 0/3 (0) |
| Indian pennywort | 2/3 (66.7) | 2/3 (66.6) | 0/3 (0) | 0/3 (0) | 2/3 (66.6) | 0/3 (0) | 0/3 (0) |
| Green leaf lettuce | 2/3 (66.7) | 2/3 (66.7) | 0/3 (0) | 0/3 (0) | 2/3 (66.6) | 0/3 (0) | 0/3 (0) |
| Chinese f. cabbage | 2/3 (66.7) | 2/3 (66.6) | 0/3 (0) | 0/3 (0) | 2/3 (66.6) | 0/3 (0) | 0/3 (0) |
| Japanese parsley | 1/3 (33.3) | 0/3 (0) | 0/3 (0) | 1/3 (33.3) | 1/3 (33.3) | 0/3 (0) | 0/3 (0) |
| Bean sprout | 0/3 (0) | 0/3 (0) | 0/3 (0) | 0/3 (0) | 0/3 (0) | 0/3 (0) | 0/3 (0) |
| Mint | 0/3 (0) | 0/3 (0) | 0/3 (0) | 0/3 (0) | 0/3 (0) | 0/3 (0) | 0/3 (0) |
| Sweet basil | 0/3 (0) | 0/3 (0) | 0/3 (0) | 0/3 (0) | 0/3 (0) | 0/3 (0) | 0/3 (0) |
| Total | 47/178 (26.4) | 42/178(23.6) | 1/178 (0.6) | 5/178 (2.80) | 40/178 (22.5) | 0/178 (0) | 7/178 (3.93) |
The EN ISO 11290-1 method is the reference method. True positive: Samples are considered true positive when the sample is positive by all the detection methods. False-positive: Samples considered as false positive when the sample is positive either by 3M™ MDA or 3M ™ petrifilm EL plate, but negative by the reference method; False negative: Samples are considered as false negative when the sample is negative by 3M™ MDA or 3M™ petrifilm EL plate but positive by the reference method
NB the value inside the brackets is the percentage