Overview
EN ISO 21567:2004 - "Microbiology of food and animal feeding stuffs - Horizontal method for the detection of Shigella spp." - is a CEN-endorsed ISO standard that specifies a harmonized, horizontal laboratory method for the detection of Shigella species in food, animal feed and environmental samples related to food production and handling. The method is intended for routine food microbiology testing and requires competent personnel working under appropriate containment and health & safety rules.
Key topics and technical requirements
- Scope and applicability: Detection (presence/absence) of Shigella spp. in products intended for human consumption, animal feeding stuffs and environmental samples in food production/handling areas.
- Four-step principle:
- Enrichment in selective liquid medium (Shigella broth with novobiocin 0.5 µg/ml), incubated anaerobically at about 41.5 ± 1 °C for 16–20 h.
- Plating onto three selective differential agars: MacConkey (low selectivity), XLD (moderate selectivity) and Hektoen enteric agar (highest selectivity), incubated at 37 °C for 20–24 h.
- Colony selection and purification on nutrient agar.
- Biochemical and serological confirmation of suspected colonies.
- Media, reagents and quality: Annex B details composition and preparation; commercial dehydrated media are recommended for consistent performance. Excessive heating or improper preparation can reduce selectivity.
- Colony morphology: Annex C describes expected colony appearances on selective agars for identification and quality control.
- Safety: The standard includes an explicit warning that the method must only be carried out by skilled personnel using good laboratory practice and suitable containment.
- Reporting: The standard defines expression of results and required test report elements.
Practical applications and users
- Ideal for food microbiology laboratories, public health and regulatory agencies performing routine surveillance for Shigella contamination.
- Used by food manufacturers, quality assurance teams and contract testing labs for batch release, environmental monitoring and outbreak investigation.
- Applicable in veterinary and feed testing where feedstuffs are assessed for human-animal food chain safety.
- Useful during incident response (foodborne outbreaks) to confirm presence/absence of Shigella in implicated matrices.
Related standards
- ISO 6887 series (sample preparation and dilutions)
- ISO 7218 (general rules for microbiological examinations)
- ISO/TS 11133-1 and -2 (culture media preparation and performance testing)
- The EN ISO 21567:2004 text is endorsed by CEN as EN ISO 21567:2004 and includes normative Annexes for media and procedures.
Keywords: EN ISO 21567:2004, Shigella spp., detection method, food microbiology, horizontal method, enrichment, selective media, serological confirmation.