ISO 20645:2004

ISO 20645:2004 - Overview

ISO 20645:2004 specifies a laboratory method - the agar diffusion plate test - for qualitatively assessing the antibacterial activity of treatments applied to woven, knitted and other flat textile materials. The method is intended mainly for hydrophilic, air‑permeable materials and for products in which the antibacterial agent can diffuse into agar. It provides a reproducible way to compare hygienic finishes and antimicrobial textile treatments, but is not suitable for treatments that chemically react with the agar.

Key topics and technical requirements

• Test principle: Two‑layer agar plates (sterile lower layer, bacteria‑inoculated upper layer). Textile specimens are placed on the agar; antibacterial activity is assessed by bacterial growth under the specimen and any inhibition zone surrounding it.
• Specimens: Circular samples, typically 25 ± 5 mm diameter; tests performed on both sides; minimum of four specimens.
• Apparatus & conditions: Incubator at 37 ± 1 °C; sterile petri dishes (9 cm); microscope (20×) for contact‑zone inspection.
• Culture media & preparation: Defined nutrient broth and agar formulations are given; pour volumes for layers are specified (lower layer ~10 ml, upper inoculated layer ~5 ml per plate). Use standardized reagents and follow sterile technique.
• Test bacteria: Typical strains specified include Staphylococcus aureus (ATCC 6538) and one gram‑negative strain such as Escherichia coli (ATCC 11229) or Klebsiella pneumoniae (ATCC 4352) from recognized culture collections.
• Incubation & assessment: Plates incubated 18–24 h after specimen placement. Measure inhibition zone width H using: H = (D − d) / 2 (where D = total diameter of specimen + inhibition zone, d = specimen diameter). Also inspect contact zone microscopically for growth.
• Safety: Work with bacteria requires trained personnel and appropriate biosafety precautions.

Applications and who uses it

• Textile R&D teams validating antimicrobial finishes and treated fibres.
• Quality control and certification laboratories performing textile testing for healthcare, sportswear, technical and home textiles.
• Manufacturers comparing the relative performance of antibacterial treatments and concentrations.
• Regulatory bodies and procurement specialists requiring standard test data for product claims.

Limitations and related guidance

• Requires that the antibacterial agent diffuses into agar; not suitable for non‑diffusible or agar‑reactive chemistries.
• For microbial strain handling, the standard references preservation procedures (e.g., EN 12353) and recommends using recognized culture collections for reproducibility.
• For quantitative or alternative antimicrobial test methods, consult the current ISO catalogue and related standards for antimicrobial textiles.

Keywords: ISO 20645, agar diffusion plate test, antibacterial activity, textile testing, antimicrobial textiles, hygienic finishes, test method.