Archives Des Sciences Vol 65, No. 4;Apr 2012 29 ISSN 1661-464X Comparison of PCR Technique with MPN Method in Identification of Coliform Bacteria in Water Hossein Aghababaee Department of Environmental engineering, Science and Research, Branch, Islamic Azad University, Tehran, Iran. Mohammad Ahmadi Jebelli (Corresponding author) Department of microbiology, Tehran University of Medical Sciences, Tehran, Iran. Tel: +989196658640 E-mail: m.ahmadijebelli@yahoo.com Hassan Izanloo Department of Environmental Health Engineering and Research center for Environment Pollutants, Qom University of Medical Sciences, Qom, Iran Saeed Tekyeh Water and wastewater Company, Qom, Iran Abstract Microbial pathogens are among factors posing significant threats to hygiene issues for water and wastewater. Thus indicator bacteria are used for detection of relative risk of fecal contamination and potential presence of pathogens in water. However, indicator organisms bear some disadvantages decreasing their effectiveness as ideal indicators of microbial pathogens in water. In addition, conventional methods for detection of these pathogenic viruses, bacteria, protozoa and worms tend to be inaccurate, time consuming and expensive. Polymerase Chain Reaction (PCR) technique has been recommended as a diagnostic technique which has been tested and brought about impressive results. In this paper, following designing primer related to genomic segment of Lac Z it is duplicated using PCR technique in order to isolate bacteria from samples of drinking water. This genomic segment encodes -galactosidase enzyme in Colifrom bacteria. Then results are compared with multiple-tube fermentation technique by MPN method. Sampling was performed in 18 wells of drinking water in Qom’s villages and samples were tested using PCR and MPN techniques. Of the total samples tested, 3 samples responded positively to MPN technique and 8 samples responded positively to PCR technique. Findings suggest higher accuracy in PCR compared to MPN. Keywords: Drinking water, Polymerase Chain Reaction (PCR), VBNC condition, -galactosidase 1. Introduction Coliform bacteria are used as indicator for fecal contamination of water and for determining potential presence of enteric pathogens in order to monitor bacteriologic health of water supply resources (Seema Tharannum et al., 2009; Bej et al. 1990). Conventional methods used for detection of Coliform bacteria are based on optional culture media. Such media allow gram negative bacteria growth and are able specifically to identify lactose consuming bacteria which can grow in EMB, m-Endo, MacConkey or brilliant green culture media (Sherfi et al., 2007; Rompré et al., 2002). Using these culture media and heating at 37 °C, total Coliforms including members of Escherichia, Enterobacter, Citrobacter, Kelebsiella genera are counted. Fecal Coliform bacteria, especially E.coli are counted in increased heating temperature up to 44.5 °C. Since E.coli is mainly seen in human feces, it is used as fecal contamination indicator of water and it is considered as a suitable indicator for monitoring water resources and potential presence of enteric