Tehran University of Medical Sciences Journal of Medical Bacteriology 2251-8649 5 1-2 2016 12 31 21 28 EN Masoumeh Ahmadi Jalali Moghadam Cellular and Molecular Research Center, Guilan University of Medical Sciences, Rasht, Iran. Hamidreza Honarmand Department of Microbiology, Guilan University of Medical Sciences, Rasht, Iran. Sajad Asfaram Meshginshahr Department of Microbiology, Lahijan Branch, Islamic Azad University, Lahijan, Iran. 2016 12 31 2016 12 31 Background: River and underground waters are main sources of tap water in Guilan, Iran. Overland wastes move into rivers during periods of heavy or extended rain that is very common in the area.Pseudomonas aeruginosa, Legionella pneumophila, and Escherichia coli are main human pathogens with water source. This study is designed to determine the load of these bacteria in main water suppliesof the area. Methods: Samples were collected directly into sterile containers, concentrated by centrifuge,inoculated in enrichment medium and incubated for 3-4 days. DNA was extracted by using commercial kit. Several rounds of PCR was performed to search P. saeroginosa, integron I, Metallo-β-lactamases gene, L. pneumophila, mip gene, and E. coli. Results: About 92.0% of the samples showed bacterial contamination as revealed by PCR with primers of 16S rRNAgene, 9.5% of the samples had L. pneumophila, and 11,1% had Pseudomonas aeruginosa,but Escherichia coli was not detected. We found the mip gene in 66.6% of the samples with L. pneumophila. Metallo-β-lactamasesgene was found in 11.1% of all samples. We also found Integrin 1 in 28.5% of the samples with P. aeruginosa. Conclusion: This study indicates that in spite of chlorination, total bacterial contamination of pot waters in the area is high and contamination with L. pneumophila and P. aeroginosa is considerable. Itmight be related to the biofilm formation and the growth of water microflora. It seems that free residual chlorine is ineffective. We suggest a more effective decontamination procedure based on modern technology. https://jmb.tums.ac.ir/index.php/jmb/article/view/227 https://jmb.tums.ac.ir/index.php/jmb/article/download/227/161