Need help understanding an anti-microbial result test

[marquinhos]

Dear all,

 

i need help to understand a result and will be very glad if someone could explain to me the result. the test was made in 26 pieces of bamboo coz i wanted to know how good is the bio agent bamboo kun against bacteria.

 

I heard that it can kill off 99% of the bacterias without any treatment thanks to the natural agent bamboo kun. i got the result in logarithm data and the tester can not or is refusing to say how good is the anti bacteria in percentage.

 

All i want to know is in percentage how was the bacteria reduction? like 80% 90%? in some cases i see 99.99%. I did the JIS Z 2801:2000 test, a japanese standard.

 

anyway, the test is below and i hope someone can help me here, and did any of u ever heard of bamboo kun?

 

thanks all

 

Marcus

 

http://s121.photobucket.com/albums/o219/mvardi/?action=view&current=test.jpg

[CharonY]

I have not heard from bamboo kun before but from what I read it is supposed to be a bacteriostaticum. That is, it prevents bacterial growth, but does not actively kill. Based on that it is kind of weird that the titer is going down after 24 hours. So according to this result it rally killed bacteria. To get the percentage you need simply to calculate:

(surviving bacteria/initial bacteria)*100.

The antimicrobial activity is simply another way of easily expressing this ratio. Here the difference of the log10 values before and after treatment is indicated. It is a simplification because the titers are usually so high that it is easier to operate with log values.

[marquinhos]

Thanks Charon for the kind reply

 

however, i am awful for maths.

 

see if it is correct

 

(190.000 / 560.000 ) * 100 = Percentage

 

is that correct?

 

Thanks once again

 

Marcus

[CharonY]

Nope. I may have phrased it wrongly. Initial bacteria in this case are the bacteria in your untreated control (the amount that live without bamboo kun).

(190000) and the survivors are those that still live after treatment (10).

So it is 10/190000*100.

[marquinhos]

oh, I see, so its basically 99.98% efficient, correct? since it killed almost all.

 

 

thanks for the great help, much appreciated.

 

Marcus

Edited February 6, 2009 by marquinhos

[CharonY]

Ack I noticed that I was still ambiguous. The ratio you get is the percentage of survivors. To get the kill rate you will have of course to subtract that value from 100%.

I suppose that is what you calculated above but the value should be even higher. That is another reason why often the logs are used. Something like 99.995% suggests a higher accuracy than the test could possibly give. Looking at the log distances gives a better idea.

[marquinhos]

thanks very much for the help Charon, much appreciated for clearing things up.

 

thanks a lot

 

Marcus

[jorge1907]

the property marq porposes fpr bamboo kun is that it's a bacteriostat (there is no word "bacteriostaticum") and it is the property to inhibiting growth of bacteria. A bactericide kills bacteria and that is what you are apparently investigating.

 

as charon informed -

(survivor #/original #) x 100 = % surviving.

but charon was completely wrong in the computation "10/190000*100 is completely wrong by the estimated counts you offered

190,000/560000 X 100 = about 33% survival or ~ 67% kill. Importantly this level of kill falls into the standard error one typically sees in such assays and says the stuff really doens't work well to kill bacteria - if at all.

 

charon - please be careful not to mislead

[marquinhos]

Thats a reply from the SGS guy in China

 

Average of the number of viable cells of bacteria on the untreated test piece after 24h is 1.9х105 ( B)

Average of the number of viable cells of bacteria on the antimicrobial test piece after 24h is <10 ©

Log value of antimicrobial activity=Log(B/C) = >4.28

Compared B with C, do not Compared Concentration of bacteria with B

 

 

Marq.

[jorge1907]

The numbers have changed in your messages marc. Indeed if you went from ~10E5 to < 10 - you have a much more substantial reduction than within the range in your prev message (190,000 from 450,000). Assume multiple reps.

 

Tell us about your treatment and control.

[CharonY]

jorge, yes, I mistranslated the German word.

However, check the OP. 10 survivors are indicated there. In his subsequent post he erroneously compared the original numbers E. coli with those of S. aureus.

[marquinhos]

Charon and Jorge

 

just talked to the guy from SGS and here is the final result and how it was conducted.

 

In my bamboo piece without any chemical (just the bamboo piece) they placed 25 ml of liquid bacteria which has 10.000 units approximately.

 

they used a film to wrap it and incubation for 24 hours

 

after that, they counted the bacteria left which were less than 10 (<10)

 

so in other words, there was 99.9% reduction as far as i know ^^

 

anyway, guess thats the final result and exactly what i wanted to know, thanks for the help and i hope u guys have learnt something new about this "Bamboo kun" which kills bacteria and is natural

 

the reason for this test is that i am releasing a new line of bamboo kitchenware and i want to explain to customers that it has a natural anti bacteria.

 

Thanks all

 

Marq.

[GDG]

What kind of bacteria are you testing? There are many, many different species, and there are widely varying environmental requirements and susceptibilities. If your bamboo kills only an innocuous lab strain, and has no effect on more pathogenic bacterial...

[CharonY]

The test in question is an (Japanese) industrial standard test, using E. coli and S. aureus.

 

It is of course virtually impossible to create a standardized test that can account for any potentially pathogenic bacteria, so for his purpose it is perfectly reasonable to use a standardized tests.

[GDG]

The test in question is an (Japanese) industrial standard test, using E. coli and S. aureus.

 

It is of course virtually impossible to create a standardized test that can account for any potentially pathogenic bacteria, so for his purpose it is perfectly reasonable to use a standardized tests.

 

My understanding is that the industrial standard requires only one strain of bacteria (either E. coli NCIMB 8545 or Staph A. ATCC 6538p).

 

While I agree that one cannot make a standardized test to cover every possible pathogen, I question the validity of testing an article against only a single strain (or even two), and on that basis labeling it "antibacterial".

[CharonY]

Well technically this is the way it is done for any antibacterial compound. In fact you could add the label "with the exception of resistant strains and species" to all but the the harshest antibacterial compounds.