ISO 20851:2017

Overview

ISO 20851:2017 defines a simplified, practical method for the microbiological examination of synthetic rubber latices. The standard specifies how to detect the presence and obtain an approximate count of viable aerobic and facultative anaerobic microorganisms in latex. Identification of organisms is explicitly outside the scope. The method uses a ready-made medium slide (typically containing TTC, agar and proteinaceous nutrients) that is dipped into the latex, incubated and compared to a model chart to report microbial load in CFU/ml.

Key topics and technical requirements

• Scope: Examination for viable aerobic and facultative anaerobic microorganisms in synthetic rubber latices; no identification.
• Principle: Dip a prepared medium slide in the latex; incubate both sides; compare colony density against a model chart to estimate count in colony forming units per millilitre (CFU/ml).
• Reagents: Ready-made medium slides (TTC/agar/tryptone or peptone formulations) and 1% sodium hypochlorite for disinfection.
• Apparatus: Standard lab equipment plus incubator (examples in the standard: 28 °C ± 2 °C for ~48 h or 36 °C ± 2 °C for ~24 h) and autoclave for sterilization.
• Sampling & procedure:
  • Sample agitation and sterile sampling per ISO 123.
  • Withdraw slide without touching media, inspect for defects, dip ~5 s (dilute viscous samples and record dilution factor F), blot excess, reseal tube.
  • Prepare a blank (expose a slide to air for the time of handling), incubate blank and sample together.
• Examination & reporting:
  • Compare both sides (n = 2) to the model chart supplied by the slide manufacturer; report the higher count and account for any dilution factor.
  • Include incubation time/temperature, dilution factor, CFU/ml and other identifying test details in the test report.
• Safety and disposal: Used slides/tubes must be decontaminated (e.g., 1% sodium hypochlorite immersion) or autoclaved; follow laboratory safety guidance.

Applications and users

• Quality control in synthetic rubber and latex manufacturing.
• Incoming inspection and storage monitoring for latex warehouses and processors.
• R&D and technical laboratories evaluating latex stability and preservative (biocide) effectiveness.
• Users: latex producers, rubber product manufacturers, QC/QA laboratories, and regulatory/compliance teams concerned with latex contamination and shelf-life issues.

Related standards

• ISO 123 - Rubber latex - Sampling (sampling procedures referenced)
• ISO 7218 - Microbiology of food and animal feeding stuffs - General requirements and guidance for microbiological examinations (laboratory practices and sterilization)

Keywords: ISO 20851, synthetic rubber latex, microorganisms, microbial count, CFU/ml, latex contamination, microbiological examination, medium slide, TTC, incubation.