Abstract: A method for testing causative bacterial species of food poisoning which is characterized by using two oligonucleotide primers that hybridize to opposite strands of bacterial DNA specifically, and flank a unique region in the target DNA and amplifying the specific fragment of the bacterial DNA, comprising the steps of:(a) hybridizing the primer to specific gene sequence of bacteria in a sample, extending the hybridized primer with deoxynucleotide triphosphates (dATP, dCTP, dGTP, and dTTP), and resultantly making the double strand nucleotide;(b) where the primer extension products are cleaved into each single strand of nucleotide by certain external force such as heat, pH and so on, one single strand functioning as a template for nucleotide extension with a primer of the other strand;(c) repeating a series of cycles involving cleavage of primer extension products, primer hybridizing, extension of the hybridized primers to amplify the specific fragment of DNA, and detecting the amplified DNA fragment; and(d) as