Mushrooms And Campylobacter: A Dangerous Duo?

Mushrooms are a popular food item and offer nutritional and therapeutic benefits. However, they can also be a source of foodborne illnesses, with bacteria such as Salmonella, Listeria, and Staphylococcus linked to mushroom-related food poisoning outbreaks. One particular concern is the presence of Campylobacter spp., a significant cause of foodborne illnesses worldwide, which has been found in Agaricus mushrooms. This bacterium can cause gastroenteritis and, while it usually resolves without treatment, it can lead to bacteremia and sepsis in some cases. The contamination of mushrooms can occur during various stages, from growth on compost to handling and storage, emphasizing the need for proper food handling and preparation techniques to minimize the risk of foodborne illnesses associated with mushroom consumption.

White button mushrooms can transmit Campylobacter

Mushrooms are a part of the fungal kingdom, similar to yeast and moulds. They are a significant nutritional and therapeutic species utilized in the human diet. However, they can be a source of bacterial infections, including Salmonella, Listeria, and Staphylococcus. While fresh mushrooms do not naturally contain harmful bacteria, they can become contaminated through various means, such as improper handling, growth on untreated compost, or cross-contamination with raw meat, poultry, or seafood.

White button mushrooms (Agaricus) are a commonly consumed variety and have been implicated in transmitting bacterial infections. Campylobacter species are frequently found on Agaricus mushrooms and are a leading cause of foodborne illnesses worldwide. Campylobacter can cause gastroenteritis and attach to intestinal mucosa cells, leading to potential health risks.

A study in Iran examined the prevalence of Campylobacter spp. in 740 Agaricus mushroom samples collected from markets. The investigation aimed to determine the frequency of virulence genes and antibiotic susceptibility in the identified Campylobacter species. The results confirmed the presence of Campylobacter spp. in the mushroom samples, highlighting the potential for these fungi to transmit the bacteria.

The transmission of Campylobacter through white button mushrooms poses a risk to human health. Campylobacter infections can result in gastroenteritis, and in some cases, the bacteria can infiltrate intestinal mucosa cells. While most Campylobacter diseases are self-limiting and resolve without treatment, severe cases may require antimicrobial therapy.

To minimize the risk of Campylobacter infection from white button mushrooms, proper food handling and preparation techniques are essential. Mushrooms should be washed thoroughly, and cross-contamination with raw meat, poultry, or seafood should be avoided. Additionally, storing mushrooms correctly, such as in a refrigerator, can help inhibit the growth of harmful bacteria.

Salmonella in mushrooms

Mushrooms are part of the fungal kingdom and are similar to yeast and moulds. Salmonella, Listeria, and Staphylococcus have all been linked to mushrooms, highlighting the need for vigilance in the industry when producing, handling, and processing this macroorganism. Salmonella Kedougou, for instance, was discovered in a batch of mushrooms in the UK in 2001 during an E. coli investigation. Surprisingly, no cases of food poisoning were attributed to this issue.

In 2018, a rare type of Salmonella was linked to the way mushrooms were being grown by suppliers in Northern Ireland. Investigations were expanded to all growers and fertiliser suppliers in Britain to assess the problem's extent. The UK Food Standards Agency advised consumers to wash and peel mushrooms if eaten raw and to cook them before consumption.

In 2020, there were two notable instances of Salmonella linked to mushrooms. The first involved dried wood ear mushrooms imported from China and distributed to restaurants in the United States. This outbreak affected at least 41 people across 10 states, with four hospitalisations. The product was recalled, and the US Food and Drug Administration recommended reconstituting dried mushrooms in boiling water to kill pathogens.

The second incident in 2020 involved Enoki mushrooms imported from Korea, which caused an outbreak of Listeriosis, a serious foodborne illness. This outbreak resulted in 36 cases, 31 hospitalisations, and four deaths.

While mushrooms can be carriers of Salmonella, it is important to note that proper handling, preparation, and cooking techniques can significantly reduce the risk of food poisoning. Consumers should always follow food safety guidelines when preparing mushrooms and other fresh produce.

Staphylococcus in canned mushrooms

Mushrooms are part of the fungal kingdom and are similar to yeast and moulds. Salmonella, Listeria, and Staphylococcus have all been linked to mushrooms, highlighting the need for vigilance in producing, handling, and processing. In 1989, an outbreak of staphylococcal food poisoning in the USA was linked to canned mushrooms from China. Staphylococcal enterotoxin, a heat-resistant toxin, was found to be the cause. This toxin can survive the canning process, which typically inactivates bacteria and spores through high temperatures.

The US authorities investigated the incident and concluded that the extensive handling of the mushrooms before canning likely created an opportunity for contamination. The mushrooms were then stored at room temperature in brine, providing an ideal environment for the toxin to persist. Nearly 100 people were affected by the outbreak, with several hospitalizations. This incident emphasizes the critical importance of stringent hygiene standards at all stages of food production to prevent bacterial contamination.

Staphylococcus is not the only pathogen associated with mushrooms. Salmonella Kedougou was detected in mushrooms in the UK in 2001, although no cases of food poisoning were attributed to this. More recently, in 2020, Salmonella Stanley was linked to dried mushrooms imported from China to the USA, affecting 55 people. Additionally, Listeria monocytogenes was found in Enoki mushrooms imported from Korea to North America in 2020, resulting in 36 cases, 31 hospitalizations, and four deaths.

Agaricus mushrooms, commonly known as white button mushrooms, are a popular variety in the human diet. However, they are fragile due to their lack of a protective cuticle and high moisture content. This makes them susceptible to mechanical degradation and pathogen attack, including Campylobacter, a common cause of foodborne illness. Campylobacter can cause bacteremia gastroenteritis and is frequently found in animal digestive tracts.

To minimize the risk of bacterial contamination, it is recommended to wash and peel mushrooms before consumption, especially if they are to be eaten raw. Additionally, dried mushrooms should be reconstituted in boiling water to kill any potential pathogens. These precautions are essential to ensure the safe consumption of mushrooms and prevent foodborne illnesses.

Preventing mushroom contamination

Mushrooms are highly susceptible to bacterial and fungal contamination. Fungi, bacteria, and yeasts can all ruin mushroom cultures. A single mould spore can contaminate an entire mushroom culture. Fungi sporophores often appear as a dust or powder-like layer on top of the substrate. They can also give the mycelium or grains a slimy appearance. The most common form of bacterial contamination in mushroom cultivation is "wet spot" or "sour rot", which appears as a dull grey slime with a sour-smelling odour.

Mushrooms are ideal hosts for a wide range of pathogens, including Campylobacter, Salmonella, Listeria, and Staphylococcus. In fact, Campylobacter species are the most common cause of foodborne illness across the world. Salmonella Kedougou was found in a batch of mushrooms in the UK in 2001, and Salmonella Stanley was found in dried mushrooms imported from China to the USA in 2020. In the same year, Listeria monocytogenes was found in Enoki mushrooms imported from Korea to North America. In 1989, canned mushrooms from China were associated with an outbreak of staphylococcal food poisoning in the USA.

To prevent mushroom contamination, it is important to maintain a sterile environment and a sterile process. Before cultivation, grains can be soaked for 12 to 24 hours at room temperature to allow endospores to germinate and be eliminated during sterilisation. During cultivation, it is important to maintain a clean and sanitised growing environment with increased air circulation and ventilation. Regularly monitor your operation for signs of contamination, such as discoloration, off-odours, abnormal growth, the presence of moulds, or the presence of insects. If contamination is detected, remove and dispose of the contaminated substrate immediately and wash affected tools with a bleach solution or alcohol.

To prevent Campylobacter infection more generally, the CDC recommends washing your hands regularly with soap and water, being careful when preparing raw meat, poultry, and seafood, drinking treated water and pasteurised milk, and being mindful when playing with or taking care of pets.

Storing mushrooms safely

Mushrooms are a popular food item with a unique earthy, umami-like flavour and meaty texture. However, they can be tricky to store due to their high water content and susceptibility to moisture, which can cause them to become slimy, discoloured, and mouldy. Here are some tips for storing mushrooms safely to maintain their freshness and quality:

Avoid Moisture

Moisture is the biggest enemy when it comes to storing mushrooms. Mushrooms have a high water content (80-90%) and are susceptible to absorbing additional moisture, which can lead to spoilage. Avoid washing mushrooms before storing them, and do not store them in a crisper drawer, as these environments tend to have high humidity levels.

Use Paper Bags or Paper Towels

To absorb excess moisture, store mushrooms in a brown paper bag or wrap them in a paper towel and place them in a bowl or a paper towel-lined zip-top plastic bag. The paper will help absorb moisture, keeping the mushrooms dry and fresh.

Refrigerate

Store mushrooms in the refrigerator, preferably on a shelf rather than in the crisper drawer. The ideal temperature for prolonging their shelf life is around 4°C, which can give them a storage life of up to seven days.

Avoid Strong Odours

Mushrooms tend to absorb odours, so avoid placing them near strong-smelling food items. Keep them in a well-ventilated area of the refrigerator to prevent them from absorbing unwanted flavours.

Freeze or Dry for Long-Term Storage

If you want to store mushrooms for an extended period, you can freeze or dry them. Freezing involves cooking the mushrooms, then placing them in a freezer-safe bag for up to 12 months. Drying mushrooms involves using a dehydrator or air-drying, then storing them in an airtight glass jar. Dried mushrooms have an intense umami flavour and can be reconstituted for use in soups, stews, or stir-fries.

Wash Before Consumption

It is recommended to wash mushrooms just before preparing, cooking, or eating them. Washing them earlier can increase their moisture content and shorten their shelf life. Peeling and washing mushrooms before consumption may also help reduce the risk of bacterial contamination, as some mushrooms have been associated with foodborne illnesses caused by Salmonella, Listeria, and Staphylococcus.

Frequently asked questions