To determine the analytical sensitivity of the assay, the
limit of detection was identified using a plasmid containing part of the 18 S rRNA gene from P. knowlesi.
Ten-fold serial dilutions of this plasmid were prepared
and served as the template in both the Plasprobe and Pk
probe real-time PCR assays (Table 1). Based on the cycle threshold (Ct) values, the Pk probe was more sensitive in detecting the target DNA sequence compared
with the Plasprobe. This was observed in all dilutions
tested. Despite this, the limit of detection was 10 copies
of template per PCR reaction for both real-time assays
and the efficiencies of the two PCR reactions were very
similar (94% for Plasprobe and 95% for Pk probe). Both
assays were linear between 10 and 106 copies of template DNA The dynamic range of the assay was determined using
serial dilutions of genomic DNA extracted from a
patient sample infected with P. knowlesi (Table 1). As
observed with the plasmid DNA, the Pk probe reaction
had lower Ct values, yet the overall sensitivity of the
two assays was similar. Both real-time PCR assays
detected P. knowlesi template over a dynamic range of 5
log dilution