Detection of Total Coliforms and Escherichia coli in drinking water by Membrane Filtration Using MI Medium in Urmia City

Background: Coliform bacteria are described and grouped, based on their common origin or characteristics, as either Total or Fecal Coliform. The Total group includes Fecal Coliform bacteria such as Escherichia coli (E .coli), as well as other types of Coliform bacteria that are naturally found in the soil. Fecal Coliform bacteria exist in the intestines of warm blooded animals and humans, and are found in bodily waste, animal droppings, and naturally in soil. The coliform group has been used extensively as an indicator of water quality and has historically led to the public health protection concept. The aim of this study was described a sensitive and differential membrane filter (MF) medium, using MI agar, for detection and enumeration of both total coliforms (TC) and Escherichia coli (E. coli) in water samples in 24 hours or less on the basis of their specific enzyme activities. Two enzyme substrates, the fluorogen 4-Methylumbelliferyl-β-D-galactopyranoside (MUGal) and a chromogen Indoxyl-β-D-glucuronide (IBDG), are included in the medium to detect the enzymes β-galactosidase and β-glucuronidase, respectively, produced by TC and E. coli, respectively.Methods: An appropriate volume of a water sample (100 mL for drinking water) is filtered through a 47-mm, 0.45-μm pore size cellulose ester membrane filter that retains the bacteria present in the sample. The filter is placed on a 5-mL plate of MI agar and the plate is incubated at 35°C for up to 24 hours. The bacterial colonies that grow on the plate are inspected for the presence of blue color from the breakdown of IBDG by the E. coli enzyme β -glucuronidase and fluorescence under longwave ultraviolet light (366 nm) from the breakdown of MUGal by the TC enzyme β –galactosidase.Result: A total of drinking water samples were analyzed using MI Medium. Total coliforms produced fluorescent colonies upon exposure to longwave ultraviolet light after primary culturing on MI agar. Escherichia coli produced blue colonies under ambient light after primary culturing on MI agar.Conclusion: MF technique is the method most widely used for the enumeration of coliforms in drinking water. This technique, simple to perform and inexpensive, requires at least an overnight incubation period and a confirmation test after the initial typical colony investigation.

کلیدواژه ها:

Escherichia coli ، drinking water ، Membrane Filtration