A Ahani Azari - Department of Microbiology, Faculty of Veterinary Medicine, University of Tehran, Tehran, Iran
T Zahraei Salehi - Bacis and Molecular Epidemiology of Gastrointestinal Disorders Research Center, Shahid Beheshti Universityof Medical Sciences, Tehran, Iran
B. Nayeri Fasaei - Department of Microbiology, Faculty of Veterinary Medicine, University of Tehran, Tehran, Iran
O Madadgar - Department of Microbiology, Faculty of Veterinary Medicine, University of Tehran, Tehran, Iran

BACKGROUND: Among all common techniques in sitedirected mutagenesis, λ Red recombinase system has been widely used to knock out chromosomal genes in bacteria. In this method, there is always the risk of DNA Linear digestion by host's restriction enzymes that leads to the low frequency of recombination. OBJECTIVES:To overcome this, we constructed a recombinant vector to disrupt phoP gene in Salmonella typhimurium. METHODS: The SOEing PCR method and restriction enzymes were used to construct the vector. RESULTS: The resulting plasmid, pTAAZ92, contains a Kanamycin cassette with two long homologous arms flanking of the phoPgene. CONCLUSIONS: After electrotransformation of the pTAAZ92 into the Salmonella typhimurium , the phoP gene is replaced by the Kanamycin cassette through homologous recombination. According to the high homology of the phoP gene in many of Salmonella species the pTAAZ92 can be used to disrupt the phoP gene in most of these species.

gene disruption, Kanamycin cassette,Salmonella typhimurium, sitedirectedmutagenesis