5 replies to this topic

[Tricia22]

Hi, I'm wondering what does <.0.3 MPN/item for E.coli mean. Can I say that my samples were positive on E.coli. And I also need help on solving the log cfu/cm². Thank you! :)

[Charles.C]

Hi, I'm wondering what does <.0.3 MPN/item for E.coli mean. Can I say that my samples were positive on E.coli. And I also need help on solving the log cfu/cm². Thank you! :)

Hi Tricia,

 

^^^(red) - No you can't. The opposite is nearer an answer.

 

<0.3 MPN/gram  "typically" means that using a specific Standard Procedure involving a 3x3 array of detection tubes as, for example, described in BAM,  has resulted in no positive detections. The associated mathematics then enables you to (statistically) claim that the Most Probable Number (MPN) of E.coli in the original sample is < 0.3 cfu per gram. (Other numbers/units are possible depending on the specific procedure).

 

^^^(blue) - Please clarify what help is required. You probably need to provide more context.

[Evans X.]

Greetings Tricia,

 

Need further clarification for a better explanation, such as this result is from a laboratory or is it a general question found in literature? In the second case it doesn't mean much. In the first case it propably means that 0.3 is the enumaration limit or LOQ of the laboratory, meaning that under that they can't produce a safe statistical result taking into consideration uncertainty of measurement etc, hence the < 0.3 MPN/item (though I believe it should be /mL or /g). Afterwards you compare this result with your legislation or own set limits from your company HACCP or anything similar. In general though this number in most cases should account as a non-detected so you should be good.

 

The log is the multiple of 10 (were log = 1), so log1 = 10, log2 = 100 or 10², log3 = 1000 or 10³ etc. For example if you are given a result of log3 4.2 this is the equal of 4.2 x 10³ which is 4200 cfu/cm². There are a couple more things to clear out but then it will be a wall of text, so use this to further expand on.

And a backward example to solve for better understanding. What log is a 14000 cfu result?

 

Regards!

 

PS: 14000 cfu = 1,4 x 10⁴ = log4 1,4.

[Charles.C]

Greetings Tricia,

 

Need further clarification for a better explanation, such as this result is from a laboratory or is it a general question found in literature? In the second case it doesn't mean much. In the first case it propably means that 0.3 is the enumaration limit or LOQ of the laboratory, meaning that under that they can't produce a safe statistical result taking into consideration uncertainty of measurement etc, hence the < 0.3 MPN/item (though I believe it should be /mL or /g). Afterwards you compare this result with your legislation or own set limits from your company HACCP or anything similar. In general though this number in most cases should account as a non-detected so you should be good.

 

The log is the multiple of 10 (were log = 1), so log1 = 10, log2 = 100 or 10², log3 = 1000 or 10³ etc. For example if you are given a result of log3 4.2 this is the equal of 4.2 x 10³ which is 4200 cfu/cm². There are a couple more things to clear out but then it will be a wall of text, so use this to further expand on.

And a backward example to solve for better understanding. What log is a 14000 cfu result?

 

Regards!

 

PS: 14000 cfu = 1,4 x 10⁴ = log4 1,4.

Hi Evans,

 

IIRC the relevant formula has no solution for all negative tubes. So the < 0.3 is derived from the mathematical result for a case where precisely 1 tube is positive. Hence the "<" interpretation. Logic vs maths

 

PS - yr logs may be a bit mixed up, eg log₁₀(1) = 0, similarly log₁₀(100,1000) =2, 3  respectively

 

<<<< The format of log is log_a(b) = n

[a in this is the base, or what we're getting the power of. b is the result. n is the power to which we have to solve a to find b].

So a⁽ⁿ⁾ = b.

Therefore, log1 means a⁽ⁿ⁾ = 1.

Anything to the power 0 = 1.

Therefore, in any case, we get 0. >>>>

[Tricia22]

Well, I have already found an article for the limit of APC so I guess I don't need to convert the CFU/swab into log cfu/cm². But I still don't know how to interpret the <0.3 MPN/swab, like I have 12 samples and all my results for E.coli are <0.3 MPN/swab. Thank you again and have a nice day!:)

 

RESULTS

V1S1

APC= 97,000 cfu/swab

E.coli= <0.3 MPN/swab

[Charles.C]

Well, I have already found an article for the limit of APC so I guess I don't need to convert the CFU/swab into log cfu/cm². But I still don't know how to interpret the <0.3 MPN/swab, like I have 12 samples and all my results for E.coli are <0.3 MPN/swab. Thank you again and have a nice day!:)

 

RESULTS

V1S1

APC= 97,000 cfu/swab

E.coli= <0.3 MPN/swab

Hi Tricia,

 

Sorry the Science was confusing.

The basic answer to yr query is that E.coli was not detected. Period.

 

It is impossible to convert CFU/swab into logcfu/cm² unless you have information about the swabbed area.