Table 3

PCR efficiency without treatment and with the DARE procedure and detection thresholds

SamplePCR efficiencya with:DTb (no. of spores)
No treatmentDARE
5 × 106 spores5 × 103 spores
Control (no sample)+++5 × 103
Baking powder+5 × 103
Baking soda+5 × 103
Bentonite++5 × 103
Cement−*+1 × 104
Chalk+++2.5 × 104
Coffee−**−**+5 × 103
Cornstarch+++5 × 103
Dust+++5 × 103
Flour
    All purpose++5 × 103
    Whole wheat++5 × 103
Laundry detergent+5 × 103
Milk powder (skim)+++5 × 103
Nondairy creamer+++5 × 103
Plaster+3 × 104
Probiotics+++5 × 103
Salt+5 × 103
Silica+−*+5 × 103
Soil+−*+5 × 103
Sugar
    Granulated+++5 × 103
    Powdered+++5 × 103
Talcum+−*+5 × 103
Tea+5 × 103
Tobacco+5 × 103
  • a +, all replicates showed positive PCR signals statistically comparable to those for positive controls; −, all replicates showed negative PCR signals; −*, one PCR replicate or more showed a negative PCR signal; −**, some replicates showed discrepant results (positive real-time PCR signals and negative results based on agarose gel analysis).

  • b DT, detection threshold of B. atrophaeus spores producing positive results with the DARE procedure.