ISO 22196

Antimicrobial Testing (Non-Porous)

ISO 22196 is a test method that quantitatively measures the antibacterial activity of plastics and other non-porous surfaces. It is a standard method established to test the ability of treated surfaces to kill (bactericidal) or prevent growth (bacteriostatic) of bacteria over 24 hours. It is a sensitive assay, able to detect low levels of antibacterial activity and achieve reproducible results, based on the Japanese Industrial Standard (JIS) Z 2801.

The ISO 22196 procedure

ISO 22196 is performed in triplicate by inoculating control and testing surfaces with bacteria.

1. sample preparation & Incubation

The sample surfaces are covered with a sterile coverslip to prevent evaporation, before being incubated for 24 hours in a humid environment at 35°C.

2. Determining Antibacterial Efficacy

Following the incubation, the antibacterial efficacy is determined. This involves recovering any remaining bacteria through rinsing the surface with a liquid neutralisation medium. The bacteria are then enumerated from this liquid by cultivating it onto a nutrient-rich solid media called agar.

3. Calculation of Bacterial Reduction

Once any remaining bacteria have grown, they are then counted, giving us the number of colony-forming units as a result. This allows us to calculate the reduction of bacteria on the treated surfaces against the control sample result or the initial number of bacteria put onto the sample.

All these steps allow us to establish whether the tested surfaces are bacteriostatic, bactericidal or support bacterial growth.

Two bacterial species are specified in the standard ISO 22196 method, which states that samples should be tested against Staphylococcus aureus and Escherichia coli. However, these can be substituted depending on the client’s needs, being able to test against more product and commercially relevant microorganisms such as MRSA, Pseudomonas aeruginosa, Campylobacter spp. or Salmonella spp.

Things to note 

Credibility of result

The method has some limitations, and some people argue that it is not an accurate representation of contamination events. While a treated surface might meet the requirements of ISO 22196, it may not show the same result in ‘real-life’ studies.

It is worth considering that the ISO 22196 test is run in laboratory conditions instead of ‘real-life’. However, the method gives bacteria their ideal growth conditions and allows us to control conditions that may otherwise interfere and mask the performance of the materials.

In ‘real-life’, you cannot control the number of bacteria that went on to the product and therefore cannot quantify the exact reduction of a set time frame. As a result, the ISO 22196 test offers a realistic alternative to assess whether a product offers a reduction in bacteria.

It is also possible to make modifications to suit the client’s needs, like different environmental conditions, inoculum concentration, UV exposure and changes to the standard 24-hour contact time. This allows different conditions to be simulated but in a controlled laboratory setting, thus ensuring a reproducible result.

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