AATCC 174 – Antimicrobial Activity Assessment of Carpets

Assessment of Antimicrobial Finishes on Carpet

The American Association of Textile Chemists and Colorists (AATCC) 174 method, titled “Antimicrobial Activity Assessment of Carpets”, is designed to test the antimicrobial activity of new carpet materials. Within the official standard method, there are 3 procedures – qualitative and quantitative assessments of the antibacterial activity (Tests I and II) and a qualitative antifungal assessment (Test III). Test I is similar to the AATCC 147 or a Zone of Inhibition test except that the test sample is placed on a single streak of bacteria instead of multiple streaks or a lawn. Test II is similar to the AATCC 100 with an adjusted inoculum volume. Test III is similar to test III of the AATCC 30 with a plate for the carpet facing up and another with it facing down.


Summary of the AATCC 174 Test I

 

  • Prior to initiating the test, molten agar is poured into a sterile petri dish and allowed to fully solidify.
  • The suspension of test microorganism is diluted 1:10 in sterile distilled water.
  • Using a sterile inoculating loop, one loopful of the diluted test microorganism is streaked in a single line approximately 75mm long in the center of the plate.
  • Test samples are cut into 25mm x 50mm rectangles and placed transversely across the inoculum streak.
  • Gentle pressure is applied to the test samples to ensure contact of the entire test sample to the surface of the agar.
  • Treated and untreated (control) samples, on the inoculated agar, are incubated for 18-24 hours at the temperature appropriate for the test microorganism.
  • After the duration of the contact time, the plates are removed from the incubator and examined for any interruption of growth around the sample.
  • If present, the clear zone is measured and recorded and a method specified formula is used to calcuate the zone of inhibition.

Summary of the AATCC 174 Test II
  • The test microorganism is prepared by growth in a liquid culture medium. Per the original method, S. aureus 6538 and K. pneumoniae 4352 are tested.
  • The suspension of test microorganism is standardized by dilution in a nutritive broth (this affords microorganisms the potential to grow during the test) or sterile saline solution.
  • Control and test carpet fibers are pre-wetted and then inoculated with microorganisms, in triplicate, ensuring that the inoculum is only in contact with the fibers.
  • Initial microbial concentrations are determined at “time zero” by elution then dilution and plating of control samples immediately after inoculation.
  • Additional inoculated control and test samples are allowed to incubate undisturbed in sealed containers at body-temperature for 24 hours.
  • After incubation, final microbial concentrations are determined. Reduction of microorganisms relative to initial concentrations and the control sample is calculated.
  • Controls are run to ensure that the neutralization/elution method effectively neutralizes the antimicrobial agent in the test sample.

Summary of the AATCC 174 Test III

 

  • The test microorganism is prepared by growth on an agar slant. Per the original method, A. niger 6275 is used.
  • The suspension of test microorganism is created by adding scrapings from a ripe slant of test microorganism to sterile water and glass beads. The concentration of spores is adjusted to 1×106 in sterile distilled water.
  • Prior to initiating the test, molten agar is poured into a sterile petri dish and allowed to fully solidify.
  • The agar is inoculated with the fungal spores.
  • Control and test samples are prewetted, placed on the agar and then inoculated with the fungal spores. Test substances should be inoculated with the carpet fibers face up and with the carpet fibers face down.
  • The petri dishes are sealed and incubated for 7 days at the appropriate temperature for the test microorganism.
  • After the contact time, the inoculated test sample is evaluated and rated based on the growth-free zone around the portion of the sample in contact with the agar and the fungal growth (if any) that is present on the face up portion of the sample.

Strengths of the AATCC 174 Test

 

  • The method evaulates the antibacterial and antifungal activity of carpets.
  • Test I is fast and inexpensive relative to other laboratory tests for antimicrobial activity.
  • Test II is quantitative and results tend to be reproducible.
  • In test III, the test substance comes into contact with a high number of spores.

Weaknesses of the AATCC 174 Test

 

  • The method does not specify passing criteria, meaning that whether or not the carpet is “antimicrobial” is ultimately decided by the company sponsoring the study.
  • Test I has some natural variability, and zones of microbial inhibition do not always have clear or regular boundaries.

Microchem Laboratory is a leading laboratory for the testing of antibacterial, antifungal and anti-algal surfaces and coatings.