TABLE 2.
Limit of detection of the automated PMS-phage assay applied to Middlebrook 7H9 broth and whole milk spiked with low numbers of M. avium subsp. paratuberculosis
| M. avium subsp. paratuberculosis strain | Sample matrix | Mean plaque count (PFU/ml)a ± SD at the following spiking level (PFU/ml) before AMS: |
LOD50 (PFU/ml) (95% confidence limit)b | ||
|---|---|---|---|---|---|
| 100-1,000 | 10-100 | 1-10 | |||
| ATCC 19698 | Broth | 111.8 ± 22.1 (4/4)a | 10.2 ± 4.0 (4/4) | 0.3 ± 0.5 (1/4) | 2.9 (0.8-11.5) |
| Milk | 28.9 ± 18.2 (4/4) | 4.5 ± 3.7 (3/4) | 0.3 ± 0.5 (1/4) | 5.0 (0.8-31.0) | |
| NCTC 8578 | Broth | 241.0 ± 48.1 (4/4) | 27.3 ± 14.8 (4/4) | 1.5 ± 1.3 (3/4) | 1.7 (0.3-9.6) |
| Milk | 34.0 ± 15.9 (4/4) | 4.0 ± 3.0 (4/4) | 0.3 ± 0.5 (1/4) | 8.4 (1.5-46.9) | |
| 796PSS | Broth | 302.0 ± 29.3 (4/4) | 28.3 ± 15.2 (4/4) | 3.5 ± 1.7 (4/4) | 1.0 (0.3-2.8) |
| Milk | 27.2 ± 16.3 (4/4) | 2.3 ± 2.6 (2/4) | 0.3 ± 0.5 (1/4) | 8.6 (2.5-28.8) | |
a
For four replicate samples. The number of samples yielding plaques after AMS per number of samples tested at that spiking level is given in parentheses.
b
Calculated using the Limit of Detection Program for Qualitative Microbiology Methods (AOAC, 2010).