Overview
EN ISO 20645:2004 - Textile fabrics - Determination of antibacterial activity - Agar diffusion plate test (ISO 20645:2004) specifies a standardized laboratory method to evaluate the antibacterial effect of treatments on woven, knitted and other flat textile materials. It is intended for hydrophilic, air‑permeable substrates or fibres with incorporated antibacterial agents where the active substance can diffuse into agar. The method gives qualitative (comparative) and semi‑quantitative information on antibacterial performance and is not suitable for treatments that chemically react with agar.
Key topics and requirements
- Test principle: Two‑layer agar plates (sterile lower layer, upper layer inoculated with bacteria). Test specimens are placed in contact with the inoculated surface and incubated; antibacterial activity is assessed by growth under the specimen and any surrounding inhibition zone.
- Test organisms: Prescribed strains include a gram‑positive (Staphylococcus aureus ATCC 6538 or equivalent) and one gram‑negative (Escherichia coli ATCC 11229 or Klebsiella pneumoniae ATCC 4352) from recognized culture collections.
- Specimen preparation: Circular specimens (25 ± 5 mm) - four specimens tested per material, tested on both sides; use unsterilized specimens unless otherwise stated; condition specimens in sterile Petri dishes for 12–24 h prior to testing.
- Culture media & reagents: Uses standard nutrient broths and agars (examples like Tryptic Soy Agar are cited); media compositions and sterilization procedures are specified.
- Apparatus & incubation: Standard microbiology equipment (incubator at 37 ± 1 °C, autoclave, water bath, stereomicroscope ×20); incubation 18–24 h.
- Assessment & evaluation: Measure inhibition zone (standard provides a calculation method) and examine contact zone under ×20 magnification. Results are classified (e.g., no growth, slight, moderate, heavy) and assessed against criteria for “good effect”.
- Safety: Tests use viable bacteria; trained personnel and appropriate biosafety procedures are required.
Applications and who uses this standard
- Textile manufacturers developing antimicrobial / hygienic finishes for medical textiles, sportswear, bedding, and PPE.
- Independent testing and certification laboratories performing comparative and quality control assessments.
- R&D teams validating new antibacterial treatments or concentrations.
- Purchasing/specification professionals who require standardized evidence of antibacterial performance.
- Useful for product claims verification, formulation optimization, and comparative benchmarking.
Related standards
- ISO 20645:2004 is the original ISO document implemented by CEN as EN ISO 20645:2004.
- The standard references microbiology practice standards for strain preservation (e.g., EN 12353) and requires use of strains from recognized culture collections.
Keywords: EN ISO 20645:2004, agar diffusion plate test, antibacterial activity, textile antibacterial testing, antimicrobial finishes, hygienic textiles.