PCR Testing for Clostridia in Canned and Processed Foods
Canned, semi-preserved and ready-to-eat foods require microbiological controls tailored to the characteristics of both the product matrix and the manufacturing process. Among the hazards to be considered are botulinum neurotoxin-producing clostridia, microorganisms found in the environment mainly in the form of spores.
The risk arises when the conditions within the food allow the spores to germinate, the vegetative cells to multiply and, subsequently, the toxins responsible for botulism to be produced.
This topic is explored in an article by Fulvia Larini, Microbiology and Molecular Biology Manager at Tentamus Agriparadigma, published in the latest issue of T‑Magazine by Tentamus Italia. The article explains how testing is performed using Real-Time PCR and clarifies a key distinction for the correct interpretation of results: detecting genes associated with the production of botulinum neurotoxins does not mean that the toxin itself is present in the food.
Which products require particular attention?
Testing is especially relevant for:
- non-acidified or non-fermented canned and semi-preserved foods;
- processed plant-based products;
- preserved meat and fish products;
- packaged sauces and food preparations;
- refrigerated ready-to-eat foods;
- products without preservatives or subjected to mild heat treatments;
- vacuum-packed foods or products packaged under other anaerobic conditions.
For these products, safety does not depend on a single parameter. pH, water activity, heat treatment, storage temperature, packaging and shelf life must be assessed together.
Does a positive result mean that the toxin is present?
No. This is one of the most important aspects to understand when interpreting the test report correctly.
ISO/TS 17919:2013 covers the PCR detection of genetic sequences associated with botulinum neurotoxins of types A, B, E and F. The method therefore identifies clostridia carrying the genes responsible for toxin production, not the toxins themselves.
| Result | Meaning |
| Negative PCR result | The targeted genetic sequences were not detected under the conditions and within the limits of the method |
| Positive PCR result | Sequences associated with clostridia potentially capable of producing toxins were detected |
| Presence of the toxin | Requires a specific test separate from the PCR detection of the microorganism |
A positive result does not demonstrate that toxin production has occurred, but it does indicate a potential concern. The result must be assessed alongside the food’s physicochemical properties, the history of the batch and the process parameters.
How the analysis is performed
The method includes:
- enriching the sample in a growth broth and incubating it under anaerobic conditions;
- applying heat treatment to a second portion to promote the germination of any spores present;
- extracting DNA from the enriched suspensions;
- amplification using Real-Time PCR;
- detecting the specific genetic sequences.
This approach makes it possible to determine the potential presence of botulinum neurotoxin-producing clostridia in the sample and obtain useful data for process control.
From analytical results to process decisions
When a positive result is obtained, the possible points at which the microorganism may have entered or developed must be investigated. The assessment may include:
- checks on raw materials and suppliers;
- verification of pH and water activity;
- review of the heat treatment;
- monitoring of processing and storage temperatures;
- assessment of the packaging system;
- shelf-life verification;
- review of critical control points and corrective actions.
The analytical result must therefore be interpreted within the context of the product, rather than as an isolated piece of information.
Testing at Tentamus Agriparadigma
Tentamus Agriparadigma is accredited for the detection of botulinum neurotoxin-producing clostridia in accordance with ISO/TS 17919:2013. The service forms part of its microbiological and molecular biology testing activities dedicated to food safety.
The laboratory specifically supports the canned-food industry and processed-food manufacturers in defining control programmes suited to the product matrix, manufacturing technology and storage conditions.