Warmer waters: EFSA warns of the spread of “fleshing-eating” bacteria in seafood

23 Jul 2024 --- According to the European Food Safety Authority’s (EFSA) latest assessment, the prevalence of Vibrio spp. bacteria in seafood will increase globally and in Europe because of climate change, especially in low salinity or brackish waters. Antimicrobial resistance (AMR) in seafood is another major concern affecting this bacteria’s spread. Resistance to last-resort antibiotics is increasingly found in some species.

“Our latest opinion on Vibrio focuses on the public health aspects of Vibrio spp. related to the consumption of seafood in the EU. The opinion thus dealt with human infections due to consumption of seafood. Human infections deriving from environmental, recreational and/or occupational exposure to vibrios were not considered,” an EFSA spokesperson, tells Nutrition Insight.

EFSA’s experts recommend carrying out a baseline survey for relevant Vibrio spp. on important seafood products at the primary production and retail levels. Gathering information and harmonizing data is a top priority at present. The survey can be used as a reference to study the effects of climate change on the presence of these bacteria in seafood.

Vibrios are aquatic bacteria found in seafood. Some strains are pathogenic and can cause gastroenteritis or severe infections. In a previous report, EFSA’s experts analyzed the possible effects climate change could have on a wide range of food safety-related issues, including Vibrio bacteria in seafood.

Threat of waterborne bacteria
Vibrios live in marine coastal waters and brackish areas where rivers meet the sea. The bacteria thrive in temperate and warm waters with moderate salinity. Vibrios can cause gastroenteritis or severe infections, such as ear infections. People become infected by consuming raw or undercooked seafood or shellfish like oysters. 

“The scientific opinion provides an overview of the prevention and control measures along the seafood chain for the relevant Vibrio spp. In particular for bivalve mollusks, of note are depuration under controlled conditions and relaying, yielding variable reductions. Further, maintaining the cold chain is required to prevent vibrios’ growth in seafood,” the spokesperson says. 

The assessment shows that AMR was detected in studies on Vibrio spp. isolates found in seafood and from Vibrio spp. isolates causing foodborne infections in Europe. Due to the limited evidence, experts recommend conducting a survey to gather comparable data.

They recommend maintaining the cold chain during processing and transportation to prevent and control Vibrio in seafood. In addition, storage is crucial for seafood intended for raw consumption.European regions with brackish and low-salinity waters are most at risk of the rapid spread of Vibrio bacteria in seafood.

The spokesperson notes: “This is particularly critical for seafood intended to be consumed raw. A mild thermal treatment of oysters in water at 50°C with or without thermal shock, (flash) freezing followed by long-term frozen storage, HPP using industrially feasible conditions or irradiation reduce vibrios in seafood.”

Possible measures to reduce Vibrio are high-pressure processing, irradiation and (flash) freezing followed by long-term frozen storage. Depuration, which involves placing live mollusks in tanks with clean, circulating seawater to filter out microbes, is recommended under controlled conditions for live oyster consumption.

The experts recommend that consumers, especially vulnerable individuals, handle and cook seafood properly and avoid consuming raw or undercooked products.

Species that cause infection
According to the spokesperson, the scientific opinion provided an overview of the Vibrio spp. of highest relevance for public health in the EU through seafood consumption, their occurrence and concentration in seafood, available analytical methods for detection and enumeration, pathogenicity to humans and virulence factors, as well as antimicrobial resistance and persistence mechanisms in different environments.

The Vibrio bacterial group comprises several species that can cause Vibriosis. In the EU, Vibrio parahaemolyticus, Vibrio vulnif icus and Vibrio cholerae have the highest relevance for public health regarding seafood consumption. 

V. parahaemolyticus can cause gastroenteritis in healthy individuals, while V. vulnif icus and V. cholerae expressing O1 and non-O139 antigens can lead to severe infections, sepsis and death in vulnerable individuals.

Vibrio parahaemolyticus was found in approximately 20% of the tested seafood samples, with one out of five positive samples containing pathogenic strains. Vibrio vulnif icus was detected in 6% of the tested seafood samples. All V. vulnif icus strains are considered potentially pathogenic.

Non-choleragenic V. cholerae was found in about 4% of the tested seafood samples. Vibrio bacteria can thrive in various aquatic environments, especially warm environments, with an ideal salt concentration. The low salinity of brackish waters, where rivers meet the sea, are a higher risk.

Effects of extreme weather
Europe has seen an increase in Vibrio infections in the last two decades due to extreme weather events such as heat waves. Warmer coastal waters have expanded the areas where Vibrio bacteria can multiply, resulting in a higher risk of infections from consuming contaminated seafood. 

European regions that are at a higher risk due to the brackish nature of the water or low salinity waters include the Baltic Sea, Baltic and North Sea transitional waters and the Black Sea, as well as coastal areas with large river inflows.

In the EFSA’s recent assessment, experts anticipate that the occurrence and levels of Vibrio in seafood will increase globally and in Europe, especially in these types of waters, due to the effects of climate change, including coastal warming and heat waves.

In other industry news, researchers from the Salk Institute, US, analyzed how plants manage iron deficiency, found it eliminates IMA1, the molecular signal for iron shortfall in roots at risk of bacterial attack. At the same time, the same molecule can make leaves more resistant to these attacks. The research suggests that the iron deficiency signaling pathway and plant immune system are “deeply intertwined.”

By Inga de Jong