Method for quantifying number of cells of bacterium in sample

The present invention addresses the problem of providing a method whereby it becomes possible to quantify the number of cells of a bacterium in a sample rapidly and with high accuracy by employing PCR method. A method which can solve the problem is a method in which the identification and quantification of bacterial cells in a sample are performed through the following steps: (1) a first PCR step of carrying out PCR method using nucleic acid derived from the sample as a template and also using a universal primer pair for the amplification of 16S rRNA gene in the bacterium to obtain a first amplification product; (2) a second PCR step of carrying out nested PCR method using a primer pair for the amplification of an internal sequence in a sequence occurring in the first amplification product obtained in the first PCR step to produce a second amplification product; and (3) a cell number quantification step of determining the number of cells of the bacterium in the sample from the quantity of the second amplification product obtained in the second PCR step using data for calibration use. In addition to the steps (1) to (3), the following steps (4) and (5) may be additionally carried out: (4) a bacterial species identification step of identifying the species of the bacterium in the sample; and (5) the bacterial cell number correction step of employing the number of cells, which has been obtained in the cell number quantification step, as a provisional number of the cells of the bacterium, and correcting the provisional number of cells on the basis of the number of copies of a 16S rRNA operon of each of the control bacterium and the bacterial species identified in the bacterial species identification step to determine the number of the cells in the sample.