Abstract: This invention is directed to a novel method for PCR amplification wherein PCR is carried out at a higher pH than the pH widely used in the art. Specifically, the buffer solution is adjusted to pH 9.0 to 11.0 at 25.degree. C. Using the present invention, DNA amplification can be successfully carried out following a simple pretreatment. In the present invention whole blood is mixed with a hypotonic solution so that a selective lysis of red blood cells takes place. The residual leukocytes are then collected. The leukocytes are mixed with a polymerization agent, primers and other necessary reagents and PCR is carried out. When the PCR solution is placed at a high temperature for DNA denaturation, the leukocytes are lysed so that the leukocyte DNA is released and can access the primers and the other necessary reactions for PCR in the solution.Cell membranes and proteins are present in the PCR reaction solution due to the lack of a protein extractive step during the pretreatment.

Abstract: A synthetic oligonucleotide which is complementary to a nucleotide sequence of a gene selected from the group consisting of the Shiga toxin gene of Shigella species, the ipaH gene of Shigella species and EIEC, the invE gene of Shigella species and EIEC, the araC gene of Salmonella species, the Verocytotoxin-1 gene of EHEC or VTEC, the Verocytotoxin-2 gene of EHEC or VTEC, the toxic shock syndrome toxin-1 gene of Staphylococcus aureus, the ctx gene of Vibrio cholerae, and the enterotoxin gene of Clostridium perfringens; a method for detecting a bacterial strain by amplifying a region of the above gene by PCR using the above oligonucleotides as primers and detecting the amplified region; and a kit for the detection of the bacterial strain.