The ASTM E2149 method, titled “Determining the Antimicrobial Activity of Immobilized Antimicrobial Agents Under Dynamic Contact Conditions” is a sensitive test, often used to measure the antimicrobial activity of non-leaching, irregularly shaped or hydrophobic surfaces. Put simply, it measures the antimicrobial activity of antimicrobial surfaces when they’re shaken around in a microbially contaminated solution.
Microchem Laboratory finds the method to be far fetched as a model system, but we conduct it regularly anyway. Why? Because it’s one of the only ways to test an irregularly shaped antimicrobial object, such as a thread, powder, or 3D molded plastic in a standardized fashion. If an antimicrobial object can be tested as a flat coupon, 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 of antimicrobial agents using standard assays. If leaching of an antimicrobial agent is detectable, neutralization of the active ingredient must be confirmed before results can be confirmed.
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 substance (1g or 4in2), and the last receives a control object (an untreated object substantially similar to the test object, without the active ingredient).
- Microbial concentration from the bacterial suspension only jars are enumerated at “time zero.”
- All jars are shaken in a wrist action shaker for a specified contact time, usually 1 hour.
- After the object is shaken in the microbial suspension for the specified contact time, the microbial concentration in all jars is determined.
- Concentration 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 untreated control, 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 untreated controls.
- A Solution Test is conducted per the method to determine leaching of the antimicrobial agent.
- If the post-test shows the presence of a “leaching antimicrobial,” then the results are deemed unreliable until it confirmed that the active ingredient was successfully neutralized.
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, or antimicrobial films. In Microchem Laboratory’s 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.
- 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.
Microchem Laboratory 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.