The Assessment of Antibacterial Finished Products
The International Standard (ISO) 20743 method, titled “Textiles – Determination of Antibacterial Activity of Antibacterial Finished Products”, is designed to test the ability of fabrics that have been treated with antimicrobial agents to prevent microbial growth and to kill microorganisms, over an 18-24 hour period. Within the official standard method, there are 3 types of quantitative tests – “Absorption Method”, “Printing Method” and “Transfer Method”. The “Transfer Method” involves inoculating the surface of an agar plate and then weighing down a piece of test sample on the inoculated agar for 60 seconds after which the sample is incubated in humid conditions for 18-24 hours before determining the final concentration of viable bacteria. The “Printing Method” uses membrane filtered bacteria that are printed onto the sample before the sample is incubated in humid conditions for 1-4 hours. The “Absorption Method”, is similar to another popular antimicrobial textile test method, AATCC 100 and is the focus of this page.
This method is based off of the Japenese Industrial Standard (JIS) method, and was adopted because there was a great need for an ISO method to determine antibacterial activity of textiles.
Summary of the ISO 20743 Test Method
- The test microorganism is prepared 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). The level of nutrition present in the nutritive broth is important, and is specified by the method. Growth of the microorganism is required on the control fabric for the test to be valid.
- Control and test fabrics are inoculated with microorganisms, in triplicate, ensuring that the inoculum is only in contact with the fabrics.
- Initial microbial concentrations are determined at “time zero” by elution then dilution and plating of control fabrics immediately after inoculation.
- Additional inoculated control and test fabrics are allowed to incubate undisturbed in sealed containers at body temperature for 18-24 hours.
- After incubation, final microbial concentrations are determined. Reduction of microorganisms relative to initial concentrations and the control fabric is calculated.
- Controls are run to ensure that the neutralization/elution method effectively neutralizes the antimicrobial agent in the test fabrics.
Strengths of the ISO 20743 Test Method
- The method parameters are more carefully spelled out than an alternative antimicrobial fabric method called AATCC 100.
- The method is quantitative and results are generally reproducible.
- The method tests for both bacteriostatic (growth-inhibiting) and bactericidal (bacteria-killing) properties on a given antimicrobial fabric.
- Microbial concentrations are standardized, and bacteria are provided with nutrients during the incubation period, which provide them with ample opportunity to grow if the test fabrics aren’t sufficiently antimicrobial.
- The method stipulates triplicate experimentation, which helps researchers estimate the precision of the individual tests and increases overall experimental accuracy.
Weaknesses of the ISO 20743 Test Method
- The relationship between product performance in the ISO 20743 method and actual outcomes, such as odor inhibition or infection control, is not well understood.
- The method is generally not accepted by U.S. EPA for so-called “health claims.”
- Test fabrics that are hydrophobic can be difficult to test with this method.
- The method does not list success criteria, meaning that whether or not the tested fabric is “antimicrobial” is ultimately decided by the company sponsoring the study.
Microchem Laboratory has a great deal of experience running ISO 20743 studies for both R&D and claims validation purposes.