Overview
ISO 8784-1:2014 specifies a standardized laboratory method for the microbiological examination of dry market pulp, paper and paperboard. It describes a disintegration-based poured-plate procedure to determine the total number of colony-forming units (CFU) of bacteria and bacterial spores per gram of material. Results are reported either on an “as received” or dry-mass basis (dry-mass per ISO 638). The method defines sample preparation, culture media, diluents, equipment, incubation and reporting requirements.
Key technical topics and requirements
- Scope and principle
- Enumeration of aerobic bacteria and bacterial spores following fiber disintegration and plating in agar; results expressed as CFU/g.
- Sample preparation
- Representative sampling referenced to ISO 186 (paper/board) and ISO 7213 (pulp). Typical test sample ~2–3 g to prepare an ~1% fibre suspension.
- Option to report on a dry-mass basis - determine dry matter per ISO 638.
- Disintegration and heat treatment
- Use a sterilizable disintegrator or high-speed blender to prepare fibre suspensions in Ringer’s solution.
- For spore counts, heat the suspension at 80 °C for 10 minutes prior to plating.
- Culture media and diluents
- Plate Count Agar (PCA) composition is specified (per litre: Tryptone 5.0 g, Yeast extract 2.5 g, Dextrose 1.0 g, Agar 15.0 g; pH 7.0 ± 0.2).
- Ringer’s solution preferred as diluent; addition of Tween 80 (20 μl/L) is recommended to aid cell release.
- Media preparation and QA guidance referenced to ISO/TS 11133.
- Incubation and enumeration
- Incubate plates at 32 °C for 48 h, then enumerate colonies (total bacteria or spores).
- Use appropriate colony-counting/magnification equipment; report culture medium and diluent details.
- Equipment and asepsis
- Sterile handling, autoclave sterilization, incubator (32 ± 2 °C), water bath (80 ± 2 °C), wide-mouth pipettes, balance (0.01 g) and sterile Petri dishes.
Applications and users
- Quality control and production monitoring in pulp and paper mills to detect and quantify bacterial contamination.
- Supplier qualification and product release testing for paper and board, especially where microbial load affects product performance or downstream processing.
- Failure investigation and process troubleshooting (e.g., slime, odor, biodeterioration).
- Contract and environmental testing laboratories, microbiologists, R&D teams and regulatory/QA personnel needing reproducible CFU data.
- Useful where bacterial spores are a concern (storage stability, recycling processes, specialty papers).
Related Standards (if applicable)
- ISO 4833 - General colony count by pour plate methods (basis for the approach)
- ISO 186 - Sampling to determine average quality (paper/board)
- ISO 7213 - Pulps - Sampling for testing
- ISO 638 - Determination of dry matter content
- ISO/TS 11133-1/-2 - Guidelines for preparation and QA of culture media
Keywords: ISO 8784-1, microbiological examination, pulp paper board, bacteria enumeration, bacterial spores, CFU, disintegration method, plate count agar, Ringer’s solution, Tween 80.