Test Method ISO 22196 Explained

Our BioLabTests team often get enquiries about the testing standards we employ to carry out efficacy microbiological testing against bacteria and fungi. This is why we decided to introduce the various test methods in our blog section, starting with ISO 22196.

What is the purpose of ISO 22196?

To put it simply, ISO 22196 is a test method that quantitatively measures the antibacterial activity on 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 a 24 hours period. It is a fairly sensitive assay, able to detect low levels of antibacterial activity and with reproducible results, based on the Japanese Industrial Standard (JIS) Z 2801.

How does the testing work?

ISO 22196 is performed in triplicates by inoculating control and test surfaces with bacteria. The sample surfaces are then covered with a sterile coverslip to prevent evaporation, before being incubated for 24 hours in a humid environment. 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 is then enumerated from this liquid by cultivating it on to a nutrient rich solid media called agar. Once this has grown it is then counted giving us a colony forming unit as a result. This allows us to calculate the reduction of the bacteria on the treated surfaces against the control sample result or the initial amount put onto the sample. All of these steps allow us to establish whether the tested surfaces are bacteriostatic, bactericidal or support bacterial growth.

What bacteria can be tested?

Two bacteria 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 client’s needs, being able to test against more product and commercially relevant microorganisms such as MRSA, Pseudomonas aeruginosa, Campylobacter spp or Salmonella spp.

How credible are the results?

The method has some limitations and some people argue that it is not an accurate representation of contamination events and 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 may be run in laboratory conditions over ‘real-life’. Yet the method gives the bacteria the ideal growth conditions and allows us to control conditions which may otherwise interfere and mask the performance of the materials. In ‘real-life’ you cannot control or know how much bacteria went on and what it was therefore reduced to or know if the control was treated identically to your test sample. As a result, the ISO 22196 offers a realistic alternative to assess whether a product offers a reduction in bacteria.

It is also possible to make modifications, like different environmental conditions, to suit the client’s needs, such as inoculum concentration, UV exposure or reduction of contact time. This allows different conditions to be simulated but with the controlled environment of a laboratory test, thus ensuring a repeatable result.