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What is multiple tube technique?

What is multiple tube technique?

2.1 The multiple-tube fermentation technique is a three-stage procedure in which the results are statistically expressed in terms of the Most Probable Number (MPN). 1 Presumptive Stage: A series of lauryl tryptose broth primary fermentation tubes are inoculated with graduated quantities of the sample to be tested.

How is MPN calculated?


  1. Using Table 4 MPN Index, it is possible to estimate the number of organisms from any combination of positive and negative test results.
  2. The MPN Table (Table 4) is based on 3 dilutions of decreasing decimal increments.
  3. Calculation Equation= MPN Index per 100mL value x the Lowest dilution factor.

What is the difference between faecal coliforms and E. coli?

Therefore, the difference between the use of E, coli and fecal-coliform bacteria is that E. coli can be used to establish standards based on an acceptable level of risk of swimming-associated illness, whereas fecal-coliform bacteria cannot.

Are MPN and CFU the same?

CFU refers to “colony forming units”, whereas MPN refers to “most probable number”. The difference is that CFU/100ml is the actual count from the surface of a plate, and MPN/100ml is a statistical probability of the number of organisms (American Public Health 2012).

What happens if you drink water with coliform bacteria?

Coliform bacteria will not likely cause illness. However, their presence in drinking water indicates that disease-causing organisms (pathogens) could be in the water system. Most pathogens that can contaminate water supplies come from the feces of humans or animals.

What is the purpose of multiple tube fermentation?

Analytical Method Multiple Tube Fermentation IntroductionThis method is prescriptive. It describes the statistical estimation of total coliform density in environmental water sources such as fresh water, surface water, ground water, etc. This test can also be applied to wastewater and effluent samples.

How many ml of water should be in a multiple tube?

Water in or entering the distribution system may generally be assumed to contain little or no pollution. In this case, it is recommended that one 50-ml plus five 10- ml volumes of water sample should be inoculated into the tubes; five tubes should each contain 10ml and one tube 50ml of double-strength medium.

How are multiple tubes used to test for coliforms?

In the multiple-tube method, a series of tubes containing a suitable selective broth culture medium is inoculated with test portions of a water sample. After a specified incubation time at a given temperature, each tube showing gas forma- tion is regarded as “presumptive positive” since the gas indicates the possible presence of coliforms.

Do you know the math for the strip tube method?

This method is a bit tricky to give you all the math for as the HST yield will vary drastically depending on your strip length and half square triangle size. However, I can tell you how wide your strips should be based on your desired HST size. As per the last three weeks, the first and second columns show your finished and unfinished HST size.