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Our group’s sample does not contain E.coli.
There is a difference existed among the results obtained from various methods is because the different uses of the methods. LST Broth
Presumptive E. coli – Gas and Fluorescense
Presumptive Coliforms – Gas and NO Fluoresense
Fluorescent colonies are presumptive E. coli
E. coli Petrifilm
Red Colonies and Purple – Total Coliforms
Purple Colonies with Gas – Presumptive E. coli
Comparison between MPN and E coli Petri film:
The use of E.coli petrifilm seems more reliable than MPN since the value of MPN is less than E.coli petrifilm in the same group. It showed that MPN method was underestimated the total coliform and E.coli numbers. The Most Probable Number test methods described in this Practical provide guidelines for detection and enumeration of bacteria of food and water origin. Then we can prevent food borne infections and diseases occurring more commonly. Disadvantages of MPN Techniques:

MPN procedure takes very long time for the confirmed test result. In MPN the results are probability calculations and cannot be accurate.MPN requires more glass wares and media. False positive results are of common occurrence. Advantages of MPN Techniques:

Interpretation of the results requires minimal experience and training as results can be got by simply observing for the presence of gas or no gas. Also, water samples with high turbidity can be analyzed, since there is no apparent deleterious effect. Furthermore, because of the dilutions used in the range of 1:0 or 1:100, toxic substances present in the sample can be diluted out. Finally, MPN technique is the effective method for analyzing samples such as muds, sludges, sediments etc.

Disadvantages of Petri film include:
There is no visual difference between the different kinds of bacteria growing on the Petri film and you can't do any testing on the colonies. No classifying as bacilli or cocci, no gram-staining, no isolating a...
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