| Treatment of the specimen before DNA amplification | No. of cysts per ml of suspension (before DNA extraction) | ||||
| 1000 (I) | 100 (II) | 30 (III) | 10 (IV) | 3 (V) | |
| PCR results (three different series of experiments) | |||||
| None | +++ | + − − | − − − | − − − | − − − |
| 95°C for 10 min* | +++ | + − − | − − − | − − − | − − − |
| NaOH 0.1 M† | +++ | + − − | − − − | − − − | − − − |
| ProtK for 10 min‡ | +++ | + − − | + − − | − − − | − − − |
| ProtK for 60 min‡ | +++ | + − − | + − − | − − − | − − − |
| ProtK for 240 min‡ | +++ | −+− | ++− | − − − | − − − |
| QIAmp® manual§ | +++ | +++ | ++−¶ | −¶ −¶ −¶ | −¶ −¶ −¶ |
| ProtK for 10 min+QIAmp‡ | +++ | +++ | +++ | + −¶ −¶ | −¶ −¶ −¶ |
| ProtK for 60 min+QIAmp‡ | +++ | +++ | +++ | + −¶ −¶ | −¶ −¶ −¶ |
| ProtK for 240 min+QIAmp‡ | +++ | +++ | +++ | + −¶ −¶ | −¶ −¶ −¶ |
| NaOH 0.1 M†+ QIAmp | +++ | +++ | ++− | + − − | − − − |
| MagNA Pure ®** | +++ | +++ | +++ | + −¶ −¶ | −¶ −¶ −¶ |
| ProtK for 10 min+MagNA Pure‡ | +++ | +++ | +++ | +++ | + −¶ −¶ |
| ProtK for 60 min+MagNA Pure‡ | +++ | +++ | +++ | +++ | + −¶ −¶ |
| ProtK for 240 min+MagNA Pure‡ | +++ | +++ | +++ | + −¶ + | −¶ −¶ −¶ |
| NaOH 0.1 M†+MagNA Pure | +++ | +++ | + − − | −+− | − − − |
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(I) to (V): concentrations corresponding to 50, 5, 1.5, 0.5 and 0.15 cysts/PCR reaction tube.
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*Specimens in microtubes were placed in a dry heater for 10 min at 95°C and kept at 20°C for 30 min before amplification; †samples were treated with NaOH (0.1 M final concentration) at 95°C for 5 min; ‡ProtK at 56°C and heat inactivation at 95°C; §QIAmp® DNA Mini Kit (Qiagen)—manual method; ¶true negative values (no delays were observed for the phHV Cts while comparing each result to those obtained with the controls for phHV, indicating the absence of inhibitors; samples showing delays or more than two Cts in comparison with controls were considered inhibited); **MagNA Pure® (Roche)—automatic extraction robot.
