ISO 22196 Test for Antimicrobial Activity of Plastics

"Measurement of Antibacterial Activity on Plastics Surfaces"

Welcome to Antimicrobial Test Laboratories' ISO 22196 Test Method Resource Page.

Below, you will find a summary of the ISO 22196 method, along with some of its strengths and weaknesses. The ISO 22196 method is designed to quantitatively test the ability of plastics to inhibit the growth of microorganisms or kill them, over a 24 hour period of contact.

Please note that ISO 22196 was modeled after JIS Z 2801, and the two methods are essentially the same.

Note: The information below is presented for educational purposes only. The current, detailed ISO 22196 test method can be purchased from ISO and other vendors.

Summary of the ISO 22196 Test:

The test microorganism is prepared, usually by growth in a liquid culture medium.
The suspension of test microorganism is standardized by dilution in a nutritive broth (this affords microorganisms the potential to grow during the test).
Control and test surfaces are inoculated with microorganisms, in triplicate, and then the microbial inoculum is covered with a thin, sterile film. Covering the inoculum spreads it, prevents it from evaporating, and ensures close contact with the antimicrobial surface.
Microbial concentrations are determined at "time zero" by elution followed by dilution and plating.
A control is run to verify that the neutralization/elution method effectively neutralizes the antimicrobial agent in the antimicrobial surface being tested.
Inoculated, covered control and antimicrobial test surfaces are allowed to incubate undisturbed in a humid environment for 24 hours.
After incubation, microbial concentrations on are determined. Reduction of microorganisms relative to initial concentrations and the control surface is calculated.

Strengths of the ISO 22196 Test:

The method is quantitative and results tend to be reproducible, provided the inoculum does not spill off of the target area after being covered with the thin film.
The method tests for both bacteriostatic (growth-inhibiting) and bactericidal (bacteria-killing) properties.
Microbial concentrations are standardized, and bacteria are provided with nutrients during the incubation period, which provides them with ample opportunity to grow if surfaces aren't sufficiently antimicrobial. This is in contrast to certain other antimicrobial tests, where microbes are "incubated" in non-nutritive suspensions, which itself may be stressful over long periods.
The method stipulates triplicate experimentation, which helps researchers estimate the precision of the individual tests and increases overall experimental accuracy.
The method includes a "pass/fail" criterion for the calculated levels of antimicrobial activity observed in test samples, making determinations of antimicrobial activity less discretionary.

Weaknesses of the ISO 22196 Test:

The ISO 22196 method is not necessarily representative of actual surface contamination events, since a relatively dilute liquid microbial inoculum is spread over a considerable surface area, and then is kept wet (usually for a period of 24 hours). Most of the time, microbial contaminants dry quickly onto surfaces. This limits the time that an aqueous medium is available to facilitate interaction between the antimicrobial surface and microorganisms. This means that ISO 22196 is a "best-case" sort of test for many products.

Though the ISO 22196 test is somewhat "best-case," it is an excellent way to quantify the antimicrobial activity level of an antimicrobial surface, especially one that is hydrophobic. Among the various tests for antimicrobial activity of surfaces, this has emerged as one of the industry standards. For more information about the ISO 22196 test for antimicrobial surfaces, Contact the Lab Today!