name of the course is microbiology in public health practice

name of the course is microbiology in public health practice

the name of the subject is water treatment

What are the three parts of the standard tests for coliform presence and quantification? In which test the Lauryl tryptose broth medium is used?

Solution

The three parts of the standard tests for coliform presence and quantification are the presumptive test,the confirmed test and the completed test.

In presumptive test,the water sample is examined with the multiple tube fermentation test or membrane filteration test.In multiple tube fermentation test,a series of water samples with different volumes are used to inoculate lauryl tryptose tubes.Tubes which show acid or gas production are considered as positive and further used for the confirmed test.Lauryl tryptose broth contains sodium lauryl sulphate as selective agent for coliforms and lactose is used as nutrient source for them.If coliforms are present ,they will ferment the lactose which produces acid and gas and further decrease in pH.

In memebrane filteration test ,the typical and atypical coliform colonies are counted and then based on that the concentartion of coliform in the water sample is calculated.Then the coliforms are tested in cofirmed test.

Confirmed test:In this test,tubes of brilliant green lactose bile broth are inoculated with the coliform colonies which obtained from the presumptive test.Production of gas in the durham tubes shows positive results.

Completed test: In this a sample from each positive brillaint green tube streaked on a plate of Macconkey agar or LES endo agr medium and incubated at 35 degrees Celcius for 24 hours.To obtain purifies isolates,isolated colonies were chosen and typical and atypical coliforms are streaked onto lauryl tryptose tubes and nutrient gar slants.The lauryl tryptose tubes show gas production in Durham tubes and the nutreint slant is used for gram staining of the microorganisms which shows gram negative bacilli.