2. Brief Review of Risks

Enoki Mushrooms and Listeria monocytogenes

25/05/2023

Abstract

 

  • Listeria monocytogenes is a pathogen almost ubiquitous in nature and may contaminate enoki mushrooms through soil, fertilisers or surroundings;
  • Human infection with Listeria monocytogenes is usually caused by drinking or eating water or food contaminated with it. Unlike many other foodborne pathogens, Listeria monocytogenes can grow in low-temperature environments, such as cold drinks, frozen desserts and refrigerators. Foods susceptible to contamination by Listeria monocytogenes include milk and dairy products, salad, seafood and ice cream;
  • Typical symptoms include fever, headache, nausea, vomiting, and gastrointestinal distress, while new-borns, the elderly, and people with a weak immune system may experience serious complications, such as sepsis and meningitis, and may even die. Critically ill pregnant women may suffer miscarriage, stillbirth, or premature delivery;
  • Listeria monocytogenes is not heat-resistant and can be easily killed by normal cooking, so the risk of infection from eating thoroughly cooked enoki mushrooms is very low;
  • The public should purchase enoki mushrooms from reputable sellers. They should also pay attention to personal hygiene and environmental hygiene when preparing enoki mushrooms and cook them thoroughly before eating.

 

Introduction

 

In recent years, there have been occasional food incidents overseas related to enoki mushrooms contaminated with Listeria monocytogenes. In some incidents, related products were removed from shelves and recalled, and large-scale investigations into outbreaks of listeriosis were carried out. As enoki mushrooms are a very common food item in Macao, relevant media information has drawn the attention of Macao residents.

 

Listeria monocytogenes and Consumption Risks

 

Listeria monocytogenes, a gram-positive, non-spore-forming, facultative anaerobic bacterium, is the only pathogenic species of the genus Listeria. Being widespread in nature, it can be found in soil, water and animal digestive tracts, and may contaminate enoki mushrooms through soil, fertilisers or surroundings. Listeria monocytogenes can grow in the temperature range of -1.8°C to 45°C. Unlike many other foodborne pathogens, Listeria monocytogenes can grow in low-temperature environments, such as cold drinks, frozen desserts and refrigerators.

 

Human infection with Listeria monocytogenes is usually caused by drinking or eating water or food contaminated with it. The incubation period ranges from 3 to 70 days. Foods susceptible to contamination by Listeria monocytogenes include milk and dairy products, meat products, vegetables, salad, seafood and ice cream. Typical symptoms include fever, headache, nausea, vomiting, and gastrointestinal distress, while severe infections may lead to complications, such as meningitis and sepsis, and even death. The bacterium can be transmitted from an infected pregnant woman to the foetus via the placenta or to the new-born via the infected birth canal. Critically ill pregnant women may suffer miscarriage, stillbirth, or premature delivery.

 

In terms of the risks of infection with Listeria monocytogenes via consumption of enoki mushrooms, consumption of contaminated enoki mushrooms not thoroughly cooked or cross-contamination due to improper practices when preparing related food will increase the risk of infection with the bacterium. However, as dishes containing enoki mushrooms are usually thoroughly cooked before consumption in Macao, and Listeria monocytogenes is not heat-resistant and can be easily killed by normal cooking, the risk of infection from eating thoroughly cooked enoki mushrooms is very low. There is no need for concern.

 

Eating habits may vary from place to place and person to person. Some may eat fresh enoki mushrooms raw, for example in salad. However, enoki mushrooms on the market in Macao are generally not ready-to-eat, and uncooked enoki mushrooms are absolutely not suitable for consumption unless grown under specific conditions or specially processed. When purchasing related products, the public should carefully check the packaging labels to obtain relevant information.

 

Regulation

 

In accordance with relevant laws and regulations of Macao, imported fresh enoki mushrooms must undergo mandatory hygiene inspection and quarantine to ensure the safety of related products on the market. The Municipal Affairs Bureau (IAM) will also monitor on worldwide food safety information or official food recall information on a daily basis, and email the information to members of the trade who have registered for the use of international information e-service. In this way, they can be kept informed of the ongoing food recalls around the world, so that appropriate prevention and control measures, such as suspension of import, suspension of sale and recalls, can be taken promptly when necessary, preventing further entry of affected food products into the local market.

 

In 2015, IAM released the “Microbiological Guidelines for Ready-to-eat Food”, setting standards for Listeria monocytogenes in food to facilitate surveillance of the microbiological content of various ready-to-eat foods and giving recommendations on specific control measures according to the assessment results. The guidelines stipulate that ready-to-eat food products which do not support growth of Listeria monocytogenes are unsatisfactory if more than 100 cfu/g are detected, and that ready-to-eat food which support growth of Listeria monocytogenes and those ready-to-eat infant food are unsatisfactory if Listeria monocytogenes is detected in 25g/ml of the sample. The food products reaching the above-mentioned levels are potentially injurious to health and/or unfit for human consumption.

 

Advice to the trade and the public

 

  • The trade should purchase enoki mushrooms from reputable suppliers to ensure the supplies come from reliable sources;
  • The public should purchase enoki mushrooms from reputable sellers;
  • Enoki mushrooms must be checked before cooking and should not be consumed if rot, mould, or discolouration is found;
  • Pay attention to personal hygiene and environmental hygiene when preparing enoki mushrooms and cook them thoroughly before eating;
  • Raw and cooked food should be kept separately, and different utensils should be used for raw and cooked or ready-to-eat food to avoid cross-contamination;
  • Refrigerated ready-to-eat food should not be stored for too long and should be used as soon as possible.

 

References:

1.     Listeria monocytogenes in ready-to-eat (RTE) foods: attribution, characterization and monitoring (Food and Agriculture Organization of the United Nations, World Health Organization). 14 December 2022

https://www.who.int/publications/i/item/9789240034969

 

2.       Listeriosis (World Health Organization). 20 February 2018

https://www.who.int/news-room/fact-sheets/detail/listeriosis

 

3.      “How to Eat Safer - Consumption Tips and Risk Analysis for Food Safety” (State Administration for Market Regulation, Chinese Institute of Food Science and Technology). June 2019

https://www.samr.gov.cn/spcjs/sjdt/202106/W020210609366991518992.pdf

 

4.       Listeria Monocytogenes (Health Bureau of the MSAR Government). January 2011

https://www.ssm.gov.mo/sam/docs/1719/1719_cf555cbd112640848fe4b6f26492d7e3_000.pdf

 

5.       Explanation of Listeria Monocytogenes in Food Safety Standards (Administration for Market Regulation of Hunan Province). 21 May 2020

http://amr.hunan.gov.cn/amr/ztx/cjxxx/202005/t20200521_12148089.html

 

6.       Listeria Monocytogenes and Its Control (Centre for Food Safety of the HKSAR Government). July 2007

https://www.cfs.gov.hk/english/multimedia/multimedia_pub/multimedia_pub_fsf_12_01.html

 

BRR 004 DAR 2023