[An efficient and accurate method for counting target molecules in phage-display peptide library].

The phage titer of samples representing the low, intermediate and high phage number was respectively determined by the double-layer agar plate (DLAP) method and real-time PCR assay. The two methods accurately measured the titer of samples. The plaques from about 1/3 double-agar layer plates could be used to determine the phage titer. The DLAP experiment should repeat 10 times with 10 microl sample each time, while the within-assay coefficient variation (CV) was 4.93%-30.38%. At the same time, the real-time PCR assay only repeated 3 times with 1 microl phage each time, while CV for within-assay ranged from 0.02% to 0.25%. Results indicated that real-time PCR is a simple and quick method for determining bacteriophage titer.