What Are Log Kills? The Difference Between 99.9% and 99.9999%

Common knowledge has us understanding that a detergent cleaner will remove more bacteria than water alone and that using a sanitizer or disinfectant is more effective than just soap and water. But do we really understand how products are measured for their effectiveness?
When dealing with issues like food production and safety, we really should take the time to make ourselves aware of how these bacteria kill levels are calculated. Because to put it simply, log kills matter.

What Are Log Kills?

When disinfecting a surface or decontaminating a facility, the efficacy of a product is measured by its log reduction, also commonly known as log kills. The term comes from the logarithm scale, which is used to indicate the percentage of bacteria killed. The term “log reduction” indicates a 10-fold reduction, which means that with every step, the number of bacteria present is reduced by 90 percent.

As an example, if there are one million bacteria present on a surface, a 1-log reduction would reduce the number of bacteria by 90 percent, or 100,000 bacteria remaining. A 2-log reduction removes 99 percent, leaving behind 10,000 bacteria, 3-log removes 99.9 percent to leave behind 1,000 bacteria, and so on through a 6-log kill, which leaves behind only one cell in one million. With this knowledge, log kills on a sanitizer label take on new meaning. The difference between a single digit can have a major impact, which is critical for food safety professionals to understand when selecting the sanitizing products that will be used in a facility.

How Log-Kill Tests Are Performed

Log kills are measured in a laboratory using time-kill tests. To determine the log reduction, the product is brought into contact with known pathogens for a certain period of time. At specified intervals, samples are removed and neutralized, then the colonies are counted. An untreated sample is also used for comparison, and typically water is applied in lieu of a sanitizer. Specimens of the untreated sample are also neutralized at the same time, and the bacterial colonies are counted for comparison purposes. The difference between the number of bacteria in the untreated sample versus the treated sample indicates the log-reduction capability of the product being tested. BouMatic sends all our teat dips to a third-party testing agency to provide us with our log kill rate data.

The Significance of Teat Dip Log Kill Rates

Because the logarithm scale is being used, the difference in log kills can be dramatic. As an example, a 2-log reduction leaves 100 times more bacteria behind than a 4-log reduction.

We have found that typically Hydrogen Peroxides teat dips generate a 5-log rate. Iodine dips on general will have a 6-log rate and Chlorine Dioxides will typically reach a 6-log or 7-log rate.

Log Kills Matter

We don’t all need to be microbiologists to implement effective sanitation protocols. We do need to understand the importance of log kills when selecting the products, we will use in our cleaning protocols on our dairies.

Source: https://blog.decon7.com/blog/what-are-log-kills