Overview
ISO 7932:2004/Amd 1:2020 is an international standard for the microbiology of food and animal feeding stuffs that specifies a horizontal colony‑count technique at 30 °C for the enumeration of presumptive Bacillus cereus. Amendment 1 (2020) supplements the original method by adding optional tests (informative Annexes C–F) for more precise identification and complementary epidemiological investigations of isolates from the B. cereus group.
Key topics and technical requirements
- Primary method: Culture-based colony-count (horizontal method) for enumeration of presumptive B. cereus at 30 °C.
- Terminology update: The amendment prefers the term “B. cereus group” (reflecting species diversity) rather than “presumptive B. cereus”.
- Optional molecular and phenotypic tests (Annexes C–F):
- PCR detection of cytK-1 / cytK-2 gene variants (Annex C) to detect cytotoxin K variants and to identify B. cytotoxicus (cytK-1 is specific to B. cytotoxicus). The annex provides validated PCR conditions, recommended controls and performance data (single-laboratory validation; high inclusivity/specificity).
- PCR detection of ces gene (Annex D) to screen for strains capable of producing cereulide, the heat-stable emetic toxin (see ISO 18465 for quantification).
- Motility test for B. anthracis screening (Annex E) - a rapid phenotypic screen with noted limitations.
- Microscopy of parasporal crystals (Annex F) to identify B. thuringiensis.
- Molecular method references and controls: Annexes reference ISO 22174, ISO 20837 and ISO 20838 for molecular biology practices and controls. PCR sensitivity ranges and control strain recommendations are included.
Practical applications and users
- Food and feed testing laboratories performing routine enumeration and risk assessment for B. cereus group in foods and animal feeding stuffs.
- Quality assurance and HACCP teams in food manufacturing and processing, for monitoring contamination and compliance.
- Public health and epidemiology labs using the optional molecular tests for outbreak investigation and strain characterization.
- Regulatory bodies and certification auditors that require standardized methods for microbiological testing and reporting.
- The standard supports food safety, contamination source-tracing, and targeted screening for toxigenic strains (e.g., cereulide producers, B. cytotoxicus).
Related standards
- ISO 18465 - cereulide quantification method
- ISO 22174 - guidance on nucleic acid amplification methods
- ISO 20837 / ISO 20838 - laboratory practices and requirements for molecular biology techniques
Keywords: ISO 7932, Bacillus cereus, colony-count, microbiology of food, PCR, cytK, ces, cereulide, B. cytotoxicus, food safety, enumeration at 30 °C.