Preliminary test of P1 primer set and detection limit determination. (A) Preliminary test of primers P1f/P1r using different concentrations of pUC18. Note that spurious bands formed by whole plasmid electrophoresis runs can occur when using high concentrations of pUC18 in the reaction. (B) Sensitivity of system P1 (uniplex PCR) determined by ten-fold serial dilution (in nanograms per microliter) of pure pUC18 DNA. NTC - no template control. MM: molecular marker, 100 bp Ladder DNA (GibcoBRL Life Technologies, USA).