Vibrio spp. have been detected in a laboratory test. Is this result alone sufficient to assess product safety? Not always. When assessing the risks associated with Vibrio, it is important not only to identify the microorganism but also to evaluate the pathogenic characteristics of the species and strain detected.
This issue is particularly relevant to the fishery products sector, including businesses that produce, import, process or use shrimp, molluscs, fish and other seafood products.
Vibrio parahaemolyticus: Why Is Detection Alone Insufficient?
Vibrio parahaemolyticus is one of the Vibrio species associated with foodborne infections. However, not all strains of this species exhibit the same pathogenic characteristics.
In its 2024 scientific opinion, the European Food Safety Authority (EFSA) highlighted the significant association between V. parahaemolyticus pathogenicity and two haemolysins:
- TDH (thermostable direct haemolysin), encoded by the tdh gene;
- TRH (TDH-related haemolysin), encoded by the trh gene.
According to data reviewed by EFSA, approximately one in five seafood samples testing positive for V. parahaemolyticus contained potentially pathogenic strains carrying the tdh and/or trh genes.
Therefore, a laboratory result stating “Vibrio parahaemolyticus – detected” does not, by itself, establish whether the identified strain possesses these pathogenicity-associated characteristics.
Additional molecular testing, such as polymerase chain reaction (PCR) targeting the tdh and trh genes, can provide valuable information for risk assessment.
Vibrio cholerae: The Importance of Serogroups and Toxin-Associated Characteristics
A similar approach applies to the assessment of Vibrio cholerae, although different characteristics are relevant to this species.
Particular attention is given to the O1 and O139 serogroups, which are associated with epidemic cholera, and the ctx gene, which is associated with cholera toxin production.
When V. cholerae is detected, further testing can help determine whether the bacterium belongs to serogroup O1 or O139 and whether it carries the ctx gene.
It is important to note that V. cholerae strains belonging to other serogroups can also cause illness. Consequently, the absence of O1 or O139 serogroup markers or the ctx gene does not automatically exclude all risks associated with V. cholerae.
How Is Vibrio spp. Assessment Regulated in the European Union?
Currently, there are no harmonised EU microbiological criteria established specifically for Vibrio spp. in fishery products.
This means that there is no single, EU-wide microbiological criterion for Vibrio spp. against which every laboratory result can automatically be classified as compliant or non-compliant.
However, the absence of harmonised criteria does not mean that the risks associated with these bacteria are disregarded.
The European Commission’s document, “Suggested line to take when performing analytical test for the research of Vibrio spp. during official controls on fishery products”, provides non-binding technical recommendations for competent authorities. Its purpose is to support a harmonised, risk-based approach to official controls on fishery products.
The document recommends that, when relevant Vibrio species are identified using culture-based methods, testing should be supplemented by molecular and/or immunological methods:
- When V. parahaemolyticus is confirmed, the presence of the tdh and trh genes should be assessed.
- When V. cholerae is confirmed, the presence of the ctx gene and/or O1 and O139 serogroup markers should be assessed.
These investigations may involve PCR, immunological methods or whole-genome sequencing (WGS).
The Commission’s document indicates that the detection of the relevant pathogenicity-associated markers suggests a potential risk to human health. Under the recommended approach to official controls outlined in the document, food products with such findings should be considered unsafe for human consumption.
Article 14 of Regulation (EC) No 178/2002 provides the legal basis for action concerning unsafe food, establishing that food must not be placed on the market if it is unsafe. Where necessary, appropriate measures may be taken to prevent products from being marketed or to ensure their withdrawal or recall.
It is therefore essential to distinguish between non-binding technical recommendations on analytical testing and the legally binding general requirement to ensure food safety.
What Does This Mean for a Company’s Laboratory Testing Plan?
Vibrio spp. provide a useful example of why laboratory testing plans should be designed with consideration not only of which microorganisms are being tested for, but also of what decisions the test results are intended to support.
Depending on the product, its intended use, the risk assessment and applicable requirements, companies should consider the following questions:
- Does the selected analytical method detect only the Vibrio genus, or can it identify individual species?
- If a positive result is obtained, is further characterisation of pathogenicity-associated markers necessary?
- Can the laboratory perform the required confirmatory or supplementary testing?
- How will the results be used when making decisions about product safety?
This does not mean that every batch of fishery products must undergo all available molecular tests. The need for testing and its scope should be determined through a product-specific risk assessment.
From Microorganism Detection to Risk Assessment
The value of laboratory testing extends beyond a simple “detected” or “not detected” result.
When assessing Vibrio spp., a broader sequence of information may be essential for informed decision-making:
WHAT HAS BEEN DETECTED → WHAT CHARACTERISTICS DOES IT POSSESS → WHAT RISK COULD IT REPRESENT?
A well-designed laboratory testing programme provides not only microbiological data but also the information needed to support scientifically informed, risk-based food safety decisions.
