Aeromonas and Plesiomonas in Water and Seafood

Aeromonas and Plesiomonas are aquatic bacteria found in fresh and brackish water, and they can contaminate seafood, produce washed in untreated water, and ready-to-eat foods. Both are associated with gastrointestinal illness and can grow at refrigeration temperatures. Good handling controls them: use safe water, keep cold food at or below 5C, cook seafood to 75C in the centre, and prevent cross-contamination between raw and ready-to-eat food. Key takeaways: Aeromonas and Plesiomonas are aquatic bacteria that live in fresh and brackish water and can contaminate seafood, produce and ready-to-eat foods.. Aeromonas species can grow slowly at fridge temperatures, so refrigeration alone does not stop them; time and temperature control still matter.. Cooking seafood so the centre reaches 75C reliably destroys both bacteria, making thorough cooking the strongest single control.. Safe water is central: use potable water for washing produce, making ice and rinsing equipment, and be cautious with product from untreated sources.. Preventing cross-contamination between raw seafood and ready-to-eat food, plus good chilling and hygiene, keeps risk low.. What are Aeromonas and Plesiomonas? Aeromonas and Plesiomonas are groups of bacteria that live naturally in aquatic environments. Aeromonas species, such as Aeromonas hydrophila, are widespread in fresh water, estuaries and the surfaces of fish and shellfish. Plesiomonas shigelloides is found in similar warm fresh and brackish waters and is often linked to seafood harvested from or exposed to these environments. Both are far less familiar than Salmonella or Listeria, but they are recognised as potential foodborne hazards. Because they are part of the natural aquatic microflora, these bacteria can be present on raw seafood without any obvious signs. They are not a marker of dirty or spoiled product on their own. Instead, they represent a background hazard that good handling, chilling and cooking are designed to control, in the same way you manage other bacteria that may arrive with raw ingredients. How do they get into food? The most common route is water. Aeromonas and Plesiomonas live in rivers, ponds, estuaries and untreated supplies, so anything that contact that water can carry them: fish and shellfish, produce irrigated or washed with untreated water, and ice made from unsafe water. Filter-feeding shellfish such as mussels and oysters can concentrate bacteria from the water they grow in, which is one reason raw and lightly cooked shellfish deserve extra care. Once in a kitchen, these bacteria can spread the same way any other contaminant does. Raw seafood juices dripping onto ready-to-eat food, shared cutting boards and knives, unwashed hands, or produce rinsed in contaminated water can all move bacteria onto food that will not be cooked again. Ready-to-eat items are the biggest concern, because there is no later cooking step to destroy anything transferred to them. Why do they matter for food safety? Both organisms are associated with gastrointestinal illness, typically presenting as watery diarrhoea, abdominal cramps and sometimes nausea. As with many foodborne bacteria, young children, older people, pregnant women and people with weakened immune systems are more vulnerable to significant illness. This guide describes what these bacteria can cause and how to prevent them; it is not a diagnosis, and anyone who is unwell should seek medical advice. What makes Aeromonas particularly worth understanding is that many strains are psychrotrophic, meaning they can grow slowly at refrigeration temperatures. Chilling still slows them and remains essential, but it does not guarantee they stop multiplying the way it does for some other pathogens. That is why refrigeration must be paired with limiting the time food spends in storage and applying strict time and temperature control throughout preparation. Temperature control and the danger zone Temperature is your primary defence. Keep cold, potentially hazardous food at or below 5C and hot food at or above 60C. The range between 5C and 60C is the temperature danger zone, where food-poisoning bacteria multiply fastest. Cook or reheat seafood and other high-risk foods so the centre reaches at least 75C, which reliably destroys both Aeromonas and Plesiomonas. Because some Aeromonas strains grow at fridge temperatures, do not treat chilled storage as indefinite safety. Rotate stock, use seafood promptly, and keep display and prep times short. When food does sit in the danger zone during preparation, apply the 2-hour/4-hour rule to the cumulative time between 5C and 60C. Under 2 hours total in the danger zone: use the food, or return it to refrigeration at or below 5C.. Between 2 and 4 hours total: use the food now, do not put it back in the fridge.. 4 hours or more total: throw the food out.. Cool cooked seafood using two-stage cooling: from 60C to 21C within 2 hours, then 21C to 5C within a further 4 hours.. Safe water, ice and produce washing Since these bacteria are waterborne, controlling water quality removes a major source of contamination. Use potable (drinking-quality) water for washing produce, rinsing equipment and hands, and for making ice that will contact food. Ice made from unsafe water is a frequently overlooked hazard, as is displaying seafood on ice made from a questionable supply. Be especially careful with produce and seafood that arrive from untreated or unknown water sources. Where you rely on rainwater, bores or other non-mains supplies, understand your risks and manage them appropriately. Buying from reputable, licensed suppliers who harvest and handle product under recognised controls is one of the simplest ways to reduce the likelihood of contamination arriving with your stock. Preventing cross-contamination in the kitchen Once raw seafood is in your kitchen, keeping its bacteria away from ready-to-eat food is critical. Store raw seafood below and separate from ready-to-eat items so drips cannot fall onto them. Use dedicated cutting boards, knives and containers for raw seafood, and clean then sanitise any surface or utensil before it touches ready-to-eat food. Personal hygiene closes the loop. Thorough handwashing after handling raw seafood, before handling ready-to-eat food, and after using untreated water prevents bacteria travelling on hands. For raw or lightly cooked seafood dishes such as ceviche, sashimi or oysters, remember there is no cook step to fall back on, so supplier controls, cold-chain integrity and clean handling carry the full weight of safety. Store raw seafood below and away from ready-to-eat foods.. Use separate, clearly identified boards and utensils for raw seafood.. Clean and then sanitise surfaces and equipment between raw and ready-to-eat tasks.. Wash hands thoroughly after handling raw seafood or untreated water.. Treat raw and lightly cooked seafood dishes as higher risk and keep them cold until service.. Where the Food Standards Code fits Australian food businesses manage aquatic bacteria within the same framework that covers all foodborne hazards. Standard 3.2.2, Food Safety Practices and General Requirements, sets the day-to-day rules for receiving, storing, protecting, processing and displaying food safely, including temperature control and protection from contamination. Standard 3.2.3 covers premises and equipment, which supports safe water use, cleaning and separation of tasks. Many food-service and retail businesses also fall under Standard 3.2.2A, which introduces food safety management tools such as a Food Safety Supervisor and food handler training. None of these standards single out Aeromonas or Plesiomonas by name, and specific requirements can vary by state, territory and business type. The point is that following the Code's general controls, good temperature management, safe water, cross-contamination control and hygiene, addresses these bacteria as part of everyday practice. Checklist: Seafood and produce come from reputable, licensed suppliers.. Cold seafood is stored at or below 5C and used promptly.. Cooked seafood reaches at least 75C in the centre.. Only potable water is used for washing, rinsing and food-contact ice.. Raw seafood is stored below and separate from ready-to-eat food.. Dedicated boards and utensils are used for raw seafood and sanitised before reuse.. Hands are washed after handling raw seafood or untreated water.. The 2-hour/4-hour rule and two-stage cooling are applied to seafood.. Common mistakes: Assuming refrigeration stops all growth, when some Aeromonas strains multiply slowly at fridge temperatures.. Making display or food-contact ice from an untreated or unknown water source.. Washing produce or rinsing equipment with non-potable water.. Using the same board or knife for raw seafood and ready-to-eat food.. Treating raw or lightly cooked seafood dishes as low risk instead of managing the cold chain and supplier controls.. Leaving seafood in the 5C to 60C danger zone for too long during preparation or display..