Viroxy's microbiologist using the vortex shaker to mix the test suspension.

EN 1656:2019

Quantitative suspension test for the evaluation of bactericidal activity of chemical disinfectants and antiseptics used in the veterinary area.

EN 1656 is a phase 2 step 1 suspension test for disinfectants intended for use in the veterinary area. The test evaluates the efficacy of the product against bacteria.


Test Conditions


The standard refers to the parameters to be observed when testing products for teat disinfection and general disinfection. This includes the test microorganism, test temperature, contact time and interfering substance.

Refer to the table below for the minimum and additional test conditions.


Test Method


In a phase 2 step 1 suspension test, 8 parts of the test product is added to 1-part test microorganism and 1-part interfering substance. The mixture is allowed to interact for the duration of the contact time. One part of the mixture is added to 8 parts of neutralizer and 1-part water for 5 minutes to halt bactericidal activity. The final mixture is then acquired and incubated for 2 days to allow surviving bacteria (if any) to proliferate. The bacterial colony is counted and compared against the original culture size.

Diagram 1: EN 1656 test method


Log Reduction


Log reduction refers to the extent to which a product is capable of reducing the number of microbes. For example, 4-log reduction means the number of microorganisms on a surface has been reduced by 10 000 times. A product that is 99.9% effective against a certain microbe is said to have achieved 3-log reduction against that microbe.

For a product to pass EN 1656, it must be able to achieve 5-log reduction against the respective test microorganisms listed in Table 1. In other words, the product must be able to kill 99.999% bacteria while meeting all the other requirements of the European standard.

Difference between test product that pass & fail EN 1656 for S. aureus

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