Determination of the total number of bacteria in water is to determine the total number of aerobic bacteria, parthenogenetic anaerobic bacteria and heterotrophic bacteria in water. The total number of bacteria in the water can be used as a marker to determine the degree of organic pollution of the water sample, the more bacteria, the greater the organic content of the water, generally by plate colony counting method to determine the total number of bacteria in the water. The purpose of this experiment is to learn and master the collection of water samples and the determination of the total number of bacteria in water samples and to understand the importance of water quality and bacterial count in drinking water.

Operation method

plate colony count

Principle

Determination of the total number of bacteria in water is to determine the total number of aerobic bacteria, parthenogenetic anaerobic bacteria and heterotrophic bacteria in water. The total number of bacteria in the water can be used as a symbol to determine the degree of organic matter contamination of the tested water samples, the more the number of bacteria, the greater the content of organic matter in the water. In this experiment, the total number of bacteria in water was determined by plate counting technique. The total number of bacterial colonies grown in 1 ml of water sample in nutrient agar medium at 37 ℃ for 24 h, as a sign of the degree of bacterial contamination of the water body, China's regulations 1 ml of tap water in the total number of bacteria shall not exceed 100.

Materials and Instruments

Water Beef paste peptone agar medium
Beef paste, peptone, sodium chloride, agar, distilled water, sodium hydroxide.
Triangular flasks with glass stoppers Petri dishes Pipettes Test tubes

Move

I. Collection and preservation of water samples
Tap water: Sterilize tap water by cauterizing it with flame for 3 min, then drain it for 5-10 min, and finally take water samples in sterile containers and send them back to the laboratory for testing.
II. Determination of total bacterial count in water
Tap water: 1 ml of water sample was sucked up with a sterile pipette and added into a sterile petri dish (3 petri dishes were repeated for each water sample), and then about 15 ml of beef paste peptone agar medium that had been melted and cooled to 45-50 ℃ was added into each of the above petri dishes, and gently rotated and shaken to make the water sample and medium mix well, and the test plate was formed after condensation. Then the plate was inverted and incubated at 37 ℃ for 24 hours.
III. Counting colonies
Remove the plate from the 24-h incubation and count the number of bacterial colonies on the plate by visual observation (when counting, colonies that look similar and are close together but not touching should be counted one by one). (When counting, colonies that appear similar, close together but not touching should be counted one by one.)

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