Study: Antimicrobial Paints Do Not Protect Against Certain Bacteria

Northwestern University researchers conducted a study in which drywall samples coated with antimicrobial paints were able to ward off all bacteria except Bacillus timonensis (pictured). Image courtesy of Northwestern University–McCormick School of Engineering.

Researchers at the Robert R. McCormick School of Engineering, a constituent school at Northwestern University (Evanston, Illinois, USA), recently published the results of a study that concluded antimicrobial paints offered limited resistance against Bacillus timonensis, a spore-forming bacterium that commonly inhabits soil but can also be found in indoor environments.

The study, which was led by Erica Hartmann, an assistant professor at the McCormick School of Engineering, tested common household bacteria on samples of drywall coated with antimicrobial, synthetic latex paints. Hartmann and her team found that all bacteria within a 24-hour period except for Bacillus. One possible reason for this is the bacterium’s resilience. “If you attack bacteria with antimicrobial chemicals, then they will mount a defense,” says Hartmann. “Bacillus is typically innocuous, but by attacking it, you might prompt it to develop more antibiotic resistance.”

Bacteria tend to thrive in warm, moist environments—by contrast, indoor spaces, which are generally dry and cold, are not conducive to their development. However, Bacillus and other spore-forming bacteria can become dormant for a time to protect themselves from hostile environments, only to reactivate once those conditions improve. For this reason, Hartman questions the efficacy of antimicrobial paints, as they only seem to allow bacteria like Bacillus to not only survive, but even thrive. Therefore, Hartmann says that “we should be judicious in our use of antimicrobial products to make sure that we’re not exposing the more harmless bacteria to something that could make them harmful.”

According to the researchers, a key problem with many antimicrobial products is that while they test well against pathogenic bacteria such as E. coli, they are not resistant to common bacteria. With that in mind, Hartmann said the goal of the project was “to see how the authentic indoor bacteria would respond to antimicrobial surfaces.”

The results of the study conducted by Hartmann and her team was published online in an article entitled “Impacts of Indoor Surface Finishes on Bacterial Viability” in the journal Indoor Air.  

Source: Northwestern University – McCormick School of Engineering,