How to control Listeria monocytogenes in an Australian food business: why it grows in the fridge, the ready-to-eat foods at risk, vulnerable groups, and…
Listeria monocytogenes is a dangerous foodborne bacterium because, unlike most pathogens, it keeps growing at fridge temperatures and mainly contaminates ready-to-eat (RTE) foods that are never reheated before serving. Thorough cooking to 75°C destroys it, but recontamination after cooking is the real problem. Controls focus on strict cleaning and sanitising, short shelf life, cold-chain discipline and protecting vulnerable groups. Always confirm requirements with your state or territory food regulator and local council. Key takeaways: Listeria monocytogenes grows slowly at normal fridge temperatures (5°C or below), so cold storage slows it but does not stop it — time and cleanliness matter as much as temperature.. The main risk is ready-to-eat food that is contaminated after cooking, because it is eaten without further heating; thorough cooking to 75°C reliably destroys the bacteria.. Listeriosis is uncommon but serious, causing severe outcomes and, in vulnerable people, death; pregnant women, newborns, older people and immunocompromised customers are most at risk.. Control it through rigorous cleaning and sanitising (Listeria forms biofilms in drains, cold rooms and slicers), short shelf life for RTE foods, and strict cold-chain management.. Businesses serving vulnerable groups — aged care, hospitals, childcare — should apply extra controls and confirm requirements with their state or territory food regulator.. How temperature affects Listeria: Condition, Effect on Listeria. Cooking to 75°C — Reliably destroys it. Fridge at 5°C or below — Slows growth but does not stop it. Colder storage (lower end of the fridge range) — Slows growth further. Freezing — Stops growth but does not reliably kill it; can resume on thawing. What is Listeria and why is it different? Listeria monocytogenes is a bacterium found widely in the environment — in soil, water, vegetation, and on raw foods. It causes listeriosis, an illness that is uncommon but far more severe than most foodborne infections. Two features make it a distinct challenge for food businesses. First, it can grow at refrigeration temperatures, so the cold storage that stops most pathogens only slows Listeria down. Second, it is hardy: it tolerates salt, survives in cool damp environments, and can establish itself in a premises for months or years if cleaning is not thorough. Because listeriosis can have a long and variable incubation period — from a few days to several weeks between eating contaminated food and becoming ill — outbreaks can be hard to trace back to a source. Grows at fridge temperatures (down to around 0°C), unlike most food-poisoning bacteria. Tolerates salt and survives in cool, moist areas of a kitchen. Long and variable incubation period, which complicates tracing. Widespread in the environment and on raw produce, so it is easy to introduce. Why the fridge doesn't stop Listeria Refrigeration is a core food safety control because keeping food at 5°C or below slows the growth of most food-poisoning bacteria. Listeria is the important exception: it continues to multiply slowly even at correct fridge temperatures. This is why simply storing ready-to-eat food cold is not enough on its own. The colder the storage the slower the growth, so keeping your cold chain tight (ideally near the lower end of the fridge range) genuinely helps — but the other essential control is time. The longer an RTE food is stored, the more opportunity Listeria has to reach a hazardous level. That is why short, well-managed shelf life is one of the most effective Listeria controls available to a food business. 5°C or below slows Listeria growth but does not prevent it. Colder storage slows growth further, so tighten your cold chain. Shorter shelf life limits how high numbers can climb. Freezing stops growth but does not reliably kill Listeria — it can survive and resume growing on thawing. Ready-to-eat (RTE) foods are the main risk Thorough cooking destroys Listeria, so the highest-risk foods are those eaten without any further heating — ready-to-eat foods. The danger usually comes from contamination after cooking (for example, a cooked chicken sliced on a contaminated board, or a salad assembled with dirty hands or equipment) rather than from the raw ingredient itself. Foods that are moist, have a longer refrigerated shelf life and support bacterial growth are the classic vehicles. Soft and semi-soft cheeses (particularly unpasteurised or surface-ripened, such as brie and camembert). Cold cooked and cured meats, pâté and deli-sliced smallgoods. Cold-smoked and ready-to-eat seafood such as smoked salmon. Pre-prepared salads, coleslaws and pre-cut fruit and vegetables (including rockmelon and raw seed sprouts). Soft-serve ice cream and unpasteurised (raw) milk and dairy products. Cold cooked chicken and other cooked RTE proteins stored for later use. Who is most at risk? Healthy adults who eat food contaminated with Listeria often experience only mild symptoms or none at all. The serious harm falls on specific vulnerable groups, for whom listeriosis can cause blood infection (septicaemia), meningitis, miscarriage, stillbirth or death. Because outcomes can be so severe, health authorities advise these groups to avoid higher-risk foods, and businesses that serve them should treat Listeria control as a priority. Pregnant women and their unborn babies — infection can cause miscarriage, premature labour or stillbirth even when the mother is only mildly unwell. Newborn babies. Older people, whose immune response declines with age. People with weakened immune systems — for example those undergoing chemotherapy, organ transplant recipients, or people with diabetes, kidney disease or HIV. How to control Listeria in your premises Because Listeria is introduced on raw foods and can establish itself in the fabric of a kitchen, control rests on stopping contamination after cooking and preventing the bacteria from setting up a home in your equipment. Listeria is notorious for forming biofilms — protective communities of bacteria — in floor drains, condensate trays, cold-room seals, and hard-to-clean equipment such as slicers, dicers and vacuum-packers. Routine cleaning that misses these harbourage points allows a persistent strain to survive and repeatedly recontaminate food. Separate raw and ready-to-eat foods rigorously — dedicated boards, equipment, storage and, ideally, preparation areas. Clean then sanitise all RTE contact surfaces; cleaning removes soil, sanitising then reduces bacteria. Deep-clean known harbourage points: drains, slicers, seals, condensate trays and cold-room floors. Fix leaks, pooling water and condensation — Listeria thrives in cool, wet niches. Practise good personal hygiene, especially handwashing before handling RTE food. Consider environmental swabbing of surfaces and drains to verify your cleaning is working. Shelf life and cold-chain management Because Listeria keeps growing in the fridge, controlling how long RTE food is held is essential. Set and enforce a realistic shelf life for made-on-site RTE items, label them with a use-by date where appropriate, and rotate stock so older product is used first. Keep the cold chain unbroken from delivery through storage, preparation and display, and monitor fridge and cold-display temperatures. For higher-risk RTE foods, the combination of correct cold storage and a short shelf life keeps any Listeria present well below hazardous levels. Follow supplier storage instructions and use-by dates, and never extend the life of an RTE product beyond what your food safety program allows. Give RTE foods a short, defined shelf life and, where appropriate, a use-by date. Store and display at 5°C or below and monitor temperatures. Rotate stock (first in, first out) and discard product past its use-by date. Keep the cold chain intact at receiving, storage, prep and service. Serving vulnerable groups Businesses that prepare food for aged-care residents, hospital patients, young children in childcare, or pregnant women carry a higher duty of care because their customers are the people most likely to become seriously ill. Some settings adopt a specific Listeria management approach that goes beyond general RTE controls. This can include avoiding the highest-risk foods altogether (for example soft cheeses, pâté, cold deli meats and pre-prepared salads for at-risk residents), shortening shelf life further, and tightening cleaning verification. Aged care in particular is subject to additional food safety requirements under the Food Standards Code (Standard 3.3.1 applies food safety programs to businesses serving vulnerable populations). Requirements and recommendations vary by setting and jurisdiction, so aged care, healthcare and childcare providers should confirm the current expectations with their state or territory food regulator and follow any sector-specific guidance that applies. Worked examples: Reviewing an aged-care menu: An aged-care kitchen serving vulnerable residents reviews its menu for Listeria risk. It avoids the highest-risk items such as soft cheeses, pâté and cold deli meats for at-risk residents, shortens the shelf life of made-on-site ready-to-eat foods, and adds drains and cold-room seals to its deep-clean schedule. Cooked chicken sliced on a dirty board: A cook slices cooked chicken for sandwiches on a board that was not cleaned after raw prep. Because the chicken is ready-to-eat and won't be reheated, any Listeria transferred can grow in the fridge. Using a dedicated, sanitised board and giving the chicken a short, dated shelf life would have controlled the risk. Checklist: Ready-to-eat foods identified and their post-cook contamination points known. Dedicated equipment, boards and storage separating raw and RTE food. RTE contact surfaces cleaned and then sanitised at correct strength and contact time. Drains, cold-room seals, condensate trays and slicers on a deep-clean schedule. RTE foods held at 5°C or below with monitored fridge and display temperatures. Short, defined shelf life on made-on-site RTE items, with stock rotation. Product past its use-by date discarded, not extended. Extra controls in place for vulnerable groups (aged care, hospitals, childcare). Cleaning, temperature and any swabbing results recorded. Common mistakes: Assuming a correctly working fridge stops Listeria — it only slows it, so shelf life still matters. Focusing only on cooking temperature and ignoring recontamination of ready-to-eat food afterwards. Cleaning food-contact surfaces but neglecting drains, seals and condensate where Listeria persists. Using the same board, slicer or knife for raw and ready-to-eat foods. Extending the shelf life of RTE products past their use-by date to reduce waste. Serving high-risk foods such as soft cheese, pâté or cold deli meats to vulnerable residents without extra controls. Treating freezing as a kill step — Listeria can survive freezing and grow again on thawing.
How to control Listeria in a food business
Identify your ready-to-eat foods and the points where they could be contaminated after cooking — slicing, portioning, salad assembly, cooling and cold storage. These are the steps to control most tightly.
Use dedicated equipment, boards, utensils and storage for RTE food, and where possible a separate preparation area or time. This stops raw-food bacteria reaching food that will not be reheated.
Cook potentially hazardous food to 75°C in the centre (or a documented equivalent time-and-temperature combination). Thorough cooking reliably destroys Listeria — the priority afterwards is preventing recontamination.
Clean to remove food soil, then apply an appropriate sanitiser at the correct concentration and contact time. Target slicers, boards, benches and utensils that touch ready-to-eat food.
Regularly clean drains, cold-room seals and floors, condensate trays and equipment that is hard to dismantle. These are where persistent Listeria strains and biofilms survive routine cleaning.
Hold RTE food at 5°C or below, give it a short defined shelf life, rotate stock and discard anything past its date. Colder storage and shorter time keep any Listeria present in check.
Monitor and log fridge and display temperatures, and consider environmental swabbing to confirm cleaning is working. Records demonstrate your controls to an authorised officer and flag problems early.
Frequently asked questions
Does keeping food in the fridge stop Listeria?
No. Listeria monocytogenes is unusual because it keeps growing slowly at normal fridge temperatures of 5°C or below. Refrigeration slows it down but does not stop it, which is why short shelf life, stock rotation and clean equipment are just as important as cold storage for ready-to-eat foods. Colder storage slows growth further, so keep your cold chain tight.
Which foods are most likely to carry Listeria?
The highest-risk foods are ready-to-eat items eaten without reheating, especially moist foods with a longer refrigerated shelf life. These include soft and unpasteurised cheeses, cold cooked and cured meats, pâté, cold-smoked seafood, pre-prepared salads, pre-cut fruit, soft-serve ice cream and raw milk. Contamination usually happens after cooking, through dirty hands or equipment.
Does cooking kill Listeria?
Yes. Thorough cooking to 75°C in the centre (or a documented equivalent time-and-temperature combination) reliably destroys Listeria monocytogenes. The main risk is not undercooking but recontamination afterwards — for example slicing cooked meat on a board that also handled raw food. That is why controlling ready-to-eat food handling and cleaning is the priority.
Who is most at risk from listeriosis?
Healthy adults usually have mild or no symptoms, but listeriosis can be severe or fatal for pregnant women and their babies, newborns, older people, and anyone with a weakened immune system. In pregnancy it can cause miscarriage or stillbirth even when the mother feels only mildly unwell, so health authorities advise these groups to avoid higher-risk foods.
How do I stop Listeria establishing in my kitchen?
Prevent it from finding a permanent home. Listeria forms biofilms in cool, wet niches such as floor drains, cold-room seals, condensate trays and equipment like slicers. Clean and then sanitise food-contact surfaces, deep-clean harbourage points on a schedule, fix leaks and pooling water, and consider environmental swabbing to verify your cleaning is actually working.
What extra care is needed in aged care or hospitals?
These settings serve the people most likely to become seriously ill, so they carry a higher duty of care and may be subject to additional food safety program requirements. Many apply extra controls such as avoiding the highest-risk foods for at-risk residents, shortening shelf life and tightening cleaning verification. Requirements vary by setting and jurisdiction, so confirm current expectations with your state or territory food regulator.
Can I rely on freezing to kill Listeria in ready-to-eat food?
No. Freezing stops Listeria growing but does not reliably kill it; the bacteria can survive and resume multiplying once food thaws. Only thorough cooking to 75°C reliably destroys Listeria. For ready-to-eat foods that are never reheated, control depends on preventing contamination after cooking, keeping the cold chain tight, and using a short, well-managed shelf life.
How does a short shelf life help control Listeria?
Because Listeria keeps growing slowly even at 5°C or below, the longer a ready-to-eat food is stored, the higher numbers can climb. A short, defined shelf life limits that time so any Listeria present stays below hazardous levels. Combine it with correct cold storage, stock rotation (first in, first out) and discarding product past its use-by date.