Disinfectant efficacy

How do we know if a disinfectant is working? What do we make out of the numbers told to us as a sales pitch? 99.9% germs killed, 99% germs killed? What does this mean? The effectiveness of a disinfectant is tested and determined in the lab. These studies show the efficacy of surface disinfectants against viruses, bacteria, fungi, etc.

How is it tested?

To understand the way disinfectant studies are conducted, it is important to know how the log reduction system works. 

Log reduction

In the context of infection control, log reduction portrays how effective the disinfectant is in eliminating the bacteria. The effectiveness is determined by the number of bacterial colonies destroyed in a given time and concentration.

Mathematically, log represents a number whose power can be raised to 10. In other words, a log reduction of 1 is equivalent to a 10-fold reduction.

The difference in the number of bacterial cells before the application of the disinfectant vs after the application of the disinfectant determines the efficacy of the product. For instance, if we take a culture of 1106 cells of E.coli at the beginning of the experiment and apply 10% dilution of the disinfectant for 10 mins, there may be a reduction in the number of cells of E.coli. If the cells are reduced by log 2, the disinfectant is 99% effective. So when a product is known to be 99% effective, it means that there are still 1104 cells of bacteria left on the surface.

The thumb rule is that for every log reduction, you add a 0.9% of effectiveness. The table below shows the same.

Now that we know what log reduction means, let’s look at procedures in the lab.

Several environmental conditions affect the potency of an antimicrobial agent and it’s effectiveness. 3 of such conditions include concentration of the disinfectant, the environment temperature and the length of exposure to the disinfectant. 

These tests determine right concentration and to time reach optimum efficacy. Praanapoorna products have been tested for their disinfectant efficacy against E.coli, S.aureus and the Adenovirus.

For test, a certain number of cells of bacteria or a virus is taken and a particular dilution and quantity of disinfectant is applied and left to react for a set amount of time. After, the number of bacteria cells are compared and the right concentration and time is determined for optimum efficacy the product.

The chart below shows the results of tests on range of Praanapoorna products.

To put this table in perspective,  if the cells reduce to Log 0, then no colonies remain. If it reduces from Log 6 to Log 1, 10 colonies remain, Log 2- 100 colonies remain, Log 3- 1000 colonies remain, and so on.

Even though 99% efficacy seems like a huge reduction in bacteria, it certainly also means that many more bacteria colonies left to destroyed. So, the next time you choose disinfectant, remember the difference that 0.9% additional efficacy makes in product.

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Reference links:

  1. https://www.endurocide.com/knowledge-base/blogs/log-reductions-a-beginners-guide-2/
  2. https://www.sciencedirect.com/science/article/abs/pii/S0964830598000249?via%3Dihub
  3. http://www.koshic.org/event/file/2013_17/3_02.pdf
  4. https://www.americanpharmaceuticalreview.com/Featured-Articles/364046-Disinfectant-Efficacy-How-Can-We-Make-It-Effective/

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