Can you explain what the MPN (Most Probable Number) method is?

Hi,

Can you explain what the most probable number method is? What means in the table e.g. 0 1 0?

Regards

A method used to estimate viable microbes in a sample by means of performing serial dilutions.

Hi Lilii

Please refer the link, 0 1 0 means MPN index per 100ml is 2.

https://support.hach...r-(mpn)-method-

Mahantesh

Back in the days of lab technician we used to call MIN Most Improbable Number as limits of variation are so large.

Still its a reasonable indicator of levels in water but time consuming to make media and pipette out multiple doses of each serial dilution.  

We have 3 tubes 10-1, 3 tubes 10 -2, 3 tubes 10-3

2 positive (10-1), 1 positive (10 -2), 0 positive (10-3)

2 1 0 this i understand, the number of positive tubes decreases with each dilution.

How the cod is posible e.g. 3 0 1?

Dear Lilii,

Thats why this method is called as Most probable number, these numbers are arrived based on the study. The above code (3 0 1) is possible even 5 0 0, 5 0 1 also possible (in case you use 5 tubes) since the dilution in the first 3 tubes is lesser than the other two dilutions i.e. first 3 tubes are one time diluted, second 3 tubes are 10 times and third 3 tubes are 100 times diluted. The last 3 tubes though 100 times diluted there is chances of getting positive since the presence of coliforms is unpredictable, it is the probability that it may also contain coliforms.

This what my understanding.

Regards

Mahantesh

Hi,

 

 

Can you explain what the most probable number method is? What means in the table e.g. 0 1 0?

 

 

Regards

Hi lilii,

Here is the expert answer -

https://www.fda.gov/...erial-dilutions

 

Thanks for the answer :)

I still have a question whether the result from MPN will be the same as from plate culture?

 

Hi lilii,

It's a simple question but the answer is less so -

(1) If by "same" you mean a numerically close number, the likelihood is "variable". A purely statistical cause for variations is illustrated here  -

dat1 - CFU-MPN.pdf   161.69KB   7 downloads

(2) If "same" implies a usefully correlated relationship, the results may again depend on the situation. This large study of  an  MPN Procedure for Enterobacteriaceae versus various alternative methodologies demonstrated no significant differences of paired MPN-CFU data  -

dat2-evaluation of MPN technique for Enterobacteriaceae.pdf   300.01KB   3 downloads

In contrast, the opposite case is illustrated in this abstract  -

Evaluation of the relationship between two different methods for enumeration fecal indicator bacteria: colony-forming unit and most probable number. (Cho KH et al)

Abstract

Most probable number (MPN) and colony-forming unit (CFU) estimates of fecal indicator bacteria (FIB) concentration are common measures of water quality in aquatic environments. Thus, FIB intensively monitored in Yeongsan Watershed in an attempt to compare two different methods and to develop a statistical model to convert from CFU to MPN estimates or vice versa. As a result, the significant difference was found in the MPN and CFU estimates. The enumerated Escherichia coli concentrations in MPN are greater than those in CFU, except for the measurement in winter. Especially in fall, E. coli concentrations in MPN are one order of magnitude greater than that in CFU. Contrarily, enterococci bacteria in MPN are lower than those in CFU. However, in general, a strongly positive relationship are found between MPN and CFU estimates. Therefore, the statistical models were developed, and showed the reasonable converting FIB concentrations from CFU estimates to MPN estimates.

 

Regardless of the above caveats it is not unusual to find microbial limits and Procedures for either  "CFU/gm" or "MPN/gm" being regarded as  interchangeable .  Strictly such micro. data should only be compared when based on the "same", appropriately validated, Procedures. Failure to follow such routines is a common cause of disagreements between laboratories.