ASTM E2149 Test for Irregularly Shaped Antimicrobial Surfaces

"Determining the Antimicrobial Activity of Immobilized Antimicrobial Agents Under Dynamic Contact Condition"

Welcome to Antimicrobial Test Laboratories' ASTM E2149 test method Resource Page.

Below, you will find a summary of the ASTM E2149 test method method, along with some of its strengths and weaknesses. The ASTM E2149 test method is designed to measure antimicrobial activity of "immobilized antimicrobial agents" under "dynamic contact conditions." Put more simply, it is designed to measure antimicrobial activity of non-leaching (non-water soluble) antimicrobials when they're shaken around in a germy liquid solution.

Antimicrobial Test Laboratories finds the method to be a bit far fetched as a model system, but we use it regularly anyway. Why? Because it's one of the ONLY ways to test an irregularly shaped antimicrobial object, such as a thread, powder, 3D molded plastic. If an antimicrobial object can be tested as a flat panel, we recommend JIS Z 2801 / ISO 22196 instead of ASTM E2149.

ASTM E2149 was designed for non-leaching (immobilized and not water-soluble) antimicrobial products or surfaces, so as part of the test, products are analyzed for leaching antimicrobial agent using standard assays. If leaching antimicrobial is detectable, then a different test method should be used, such as JIS Z 2801 or ASTM E2180.

Note: The summary presented below is for educational purposes only - to purchase a copy of the full, current ASTM E2149 test method from ASTM, visit http://www.astm.org/Standards/E2149.htm

Summary of the ASTM E2149 test method:

The test microorganism is grown in liquid culture.
The concentration of the test microorganism is standardized.
The microbial culture is diluted in a sterile buffer solution.
For each product to be tested, 50 mL of the standardized microbial culture is placed into 3 containers (sterile glass jars work well).
One jar receives only bacterial suspension, another receives the antimicrobial test object, and the last receives a control object (an untreated object substantially similar to the test object, without the active ingredient).
Microbial concentrations in the liquid from all jars are enumerated at "time zero."
All jars are shaken in a wrist action shaker for some period, usually 1-24 hours.
After the object is shaken in the microbial suspension for the contact period, a small volume of the suspension is re-analyzed for "leached" antimicrobial and then microbial concentrations in all jars are determined once again.
Concentrations of microorganisms in the jar that contained the antimicrobial product are compared to either the jar that contained only microbial suspension or the jar that contained the control object, depending on certain circumstances specified by the method.
A product is said to be "antimicrobial" if it produces a substantial reduction relative to either the inoculum or object controls.
If either the pre-test or the post-test shows the presence of "leaching antimicrobial," then the results are invalidated.

Strengths of the ASTM E2149 Test Method:

The ASTM E2149 method clearly specifies the target initial microbial concentration, allowing for a fairly reproducible comparison of different antimicrobial products.
The ASTM E2149 method is written to allow experimental flexibility, which allows researchers to adapt the method to test antimicrobial products of various shapes and sizes.

Weaknesses of the ASTM E2149 Test Method:

Although this method is routinely used by manufacturers of antimicrobial surfaces, it is removed from actual usage of most antimicrobial products.
The types of products commonly tested by this method include antimicrobial countertops, antimicrobial toilet seats, antimicrobial pens, antimicrobial films, and the like.In Antimicrobial Test Laboratories' experience, many products that "pass" the ASTM E2149 test do not produce an appreciable antimicrobial effect in more realistic situations (such as when a dilute suspension of bacteria is placed directly on the product and then re-analyzed an hour later - often there is no difference between the "antimicrobial" sample and a negative control sample).
Results of the ASTM E2149 method are highly dependent on the contact time chosen for the study. An antimicrobial surface that "passes" at one hour of contact is almost certainly more effective than a surface that "passes" at 24 hours contact, but most products are tested with a 24 hour contact.
The methods used to detect "leaching antimicrobial" are not sufficiently sensitive, meaning that it's possible for reductions in microbial concentrations to be brought about by "leached" antimicrobial in the shaking solution that is not detectable by the "leaching test" methods of ASTM E 2149.
There is no clear criteria set by the method with respect to what constitutes "antimicrobial activity." For borderline products, such a decision usually falls to the study sponsor.

Antimicrobial Test Laboratories takes great care to carry out the ASTM E2149 test method as put forth by ASTM and also in accordance with the spirit of the method. Though the ASTM E2149 method has some drawbacks, it is relied upon heavily in the industry and can serve to benchmark your company's products against those offered for sale by other companies.

One aspect of testing "treated articles" (which are normally exempt from EPA data review) is that there is ample opportunity to develop scientifically defensible and realistic test models to verify antimicrobial efficacy. If your company's antimicrobial product or antimicrobial technology is particularly efficacious, we would love to talk with you about setting up a custom test that will help to differentiate your company's product in the marketplace.

For more information about the ASTM E2149 Test, Contact the Lab Today!