Overview
ISO 21567:2004 - Microbiology of food and animal feeding stuffs - Horizontal method for the detection of Shigella spp. specifies a standardized, horizontal method for detecting Shigella species in food, animal feed and related environmental samples in food production and handling areas. The standard defines the overall workflow from sample preparation to biochemical and serological confirmation, and includes safety guidance requiring skilled personnel and appropriate containment.
Key Topics and Requirements
- Scope and applicability: Intended for products for human consumption, animal feeding stuffs, and environmental samples (with noted limitations for some product types).
- Safety: Work must be performed by trained personnel using good laboratory practice and appropriate containment; infectious waste disposal must follow national regulations.
- Sample preparation: Follow ISO 6887 series and ISO 8261 for representative sampling and initial dilutions. Analysis should start quickly because Shigella survival is poor.
- Enrichment: Use Shigella broth containing novobiocin (0.5 µg/ml); incubate anaerobically at 41.5 ± 1 °C for 16–20 h.
- Selective plating: Inoculate enrichment onto three selective differential agars - MacConkey (low selectivity), XLD (moderate) and Hektoen enteric (highest) - incubating at 37 ± 1 °C for 20–24 h.
- Colony selection and confirmation: Select typical or suspect colonies (recommendation to test up to five per plate), purify on nutrient agar, then perform biochemical and serological confirmation. Commercial ID kits validated by the user may be used.
- Documentation and annexes: Annexes provide a test procedure diagram, media compositions and preparation, and descriptions of Shigella colony morphology for identification and quality control.
Applications and Who Uses It
ISO 21567:2004 is used by:
- Food microbiology laboratories for routine testing and outbreak investigations
- Regulatory authorities for surveillance and compliance testing
- Food manufacturers and quality teams for supplier verification and product safety monitoring
- Veterinary diagnostic and feed testing labs
- Environmental monitoring teams in food production and handling facilities
Practical recommendations include plating larger surface areas or duplicate plates when low-level contamination is suspected (e.g., during outbreak investigations) and re-incubating plates if initial growth is weak.
Related Standards
- ISO 6887 (sample preparation and dilutions)
- ISO 7218 (general microbiological examination rules)
- ISO 8261 (milk and milk products sampling guidance)
- ISO/TS 11133-1 and 11133-2 (culture media preparation and quality/performance)
Keywords: ISO 21567:2004, detection of Shigella spp., horizontal method, food microbiology, selective enrichment, MacConkey, XLD, Hektoen enteric, novobiocin, food safety.
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