ASTM E1428 “Pink Stain Test”
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The ASTM E1428 standard is used to evaluate the ability of synthetic polymeric materials containing antimicrobial agents to resist such staining, using the indicator staining organism Streptoverticullium reticulum.
Some materials may become discolored or stained when microorganisms grow on them in the environment.
The ASTM E1428 method is straightforward and reproducible when conducted in a consistent fashion.
Summary of the ASTM E1428 Test
- Cells of S. reticulum are harvested from a culture plate and swabbed over the entire surface fresh agar plates.
- Test specimens are transferred to inoculated plates by placing test surfaces face down.
- Test containers are covered to ensure high humidity and incubated for 14 days.
- After the desired incubation period, specimens are inspected for staining.
Strengths of the ASTM E1428 Test
- The method can be used to test virtually any flat polymeric material.
- Pink staining is easy to visually examine.
- Staining can be evident in as few as 7 days, and tests are completed in 14 days.
- Leachable biocides generate visual zones of inhibition on plates.
Weaknesses of the ASTM E1428 Test
- Staining cannot easily be determined on dark materials.
- Non-pink staining can occur, which can make rating materials challenging to laboratory staff.
- The method doesn’t account for the possibility of staining from other organisms.