Food Safety Focus (213rd Issue, April 2024) – Article 1
Bongkrekic Acid – Uncommon but Fatal Toxin in Certain Foods
Reported by Dr. Ken CHONG, Scientific Officer
Risk Assessment Section, Centre for Food Safety
In late March 2024, Taiwan's health authority reported a food poisoning outbreak at a restaurant in Taipei, resulting in 34 illnesses and two fatalities. Clinical specimens of 33 individuals were tested positive for the toxin bongkrekic acid. It was reported that a chef’s hands were tested positive for the toxin, suggesting that the food handled by the chef might have been contaminated. Suspected incriminated food included flat rice noodles and Char Kway Teow. In this article, we will get to know more about this fatal toxin and ways to reduce the risk.
What is Bongkrekic Acid
Bongkrekic acid is a heat-stable toxin produced by the bacterium Burkholderia gladioli pathovar cocovenenans (B. cocovenenans), which is ubiquitous in soil and plants. The temperature range for bacterial growth is between 30 and 37ºC and that for toxin production is between 22 and 30ºC. Cases of bongkrekic acid poisoning were originally reported as a result of consuming fermented corn and coconut-based products. Certain fatty acids, particularly those found in coconut and corn, can facilitate growth of the bacteria and production of the toxin.
Target organs of the toxin mainly include the liver, the brain and kidneys, causing symptoms including a lack of energy, dizziness, drowsiness, abdominal pain and vomiting. The incubation period for the illness is reported to be between 30 minutes and 12 hours. In severe cases, death can occur within 1 to 20 hours after the onset of symptoms. According to the review of national surveillance conducted in the Mainland, previous outbreaks have resulted in a high mortality rate of up to 60 percent.
Food Items with Emerging Risk
In recent years, outbreaks of bongkrekic acid poisoning due to the consumption of certain soaked mushrooms and wet rice noodles have been reported in Guangdong and Zhejiang. The mushrooms implicated in these outbreaks were silver ear fungus (snow fungus) and black fungus, with more cases involving the latter reported . Typically, these mushrooms were found to be soaked for more than two days in these outbreaks, while it was generally believed that bongkrekic acid would unlikely be formed when these mushrooms were soaked for only a short period of time under normal conditions.
Wet starch products or wet rice noodle products (using rice as the main raw material) is another type of food linked to outbreaks in the past few years. Similarly, the main cause of toxin production was believed to be prolonged storage at room temperature, specifically, storage for longer than 24 hours. In certain instances, the illegal use of a preservative called sodium dehydroacetate was uncovered. This preservative can inhibit the growth of some fungus and spoilage bacteria but not B. cocovenenans, resulting in a potential risk of bacterial growth without sensory changes when the noodles are spoiled.
Figure 1: Flat rice noodles and black fungus
Good Hygiene Practices for Prevention
Bongkrekic acid is produced in certain high-risk food items when they are left at room temperature for an extended period of time, typically more than a day. For prevention, it is important to maintain time and temperature control of these high-risk food items, even before cooking. For silver ear fungus or black fungus, they should be soaked under refrigeration, if it is necessary to soak them overnight. Wet rice noodle products should be kept at refrigeration temperature during transportation, storage, and sale, if the shelf life is more than one day. This becomes particularly important during warmer months when the temperature is favourable for the growth of B. cocovenenans. Additionally, to minimise the risk of contamination with microorganisms, it is crucial to practice good food hygiene at all times.
Key Points to Note
- Bongkrekic acid is a heat-stable toxin produced by the bacterium B. cocovenenans, originally reported in fermented corn and coconut-based products. The consumption of these products has been associated with outbreaks that have a high fatality rate.
- Outbreaks due to the consumption of black fungus and wet rice noodles have been reported in the past few years, which were typically caused by leaving these food items under ambient condition for more than a day.
- To prevent this uncommon but fatal toxin, apart from maintaining good food hygiene, it is important to maintain time and temperature control of the high-risk food items, even before cooking, to minimise the growth of B. cocovenenans that may be present due to contamination.
Advice to the Trade
- Ensure that wet rice noodles or like products are properly covered or packaged when they are delivered to premises.
- Wet rice noodles or like products should be kept under refrigeration during transportation, storage and sale, if the shelf life is more than one day.
- For delivery at room temperature, make sure the delivery has not taken longer than the agreed transportation time. It is also advisable to store any stock that is not intended for immediate use in the refrigerator.
Advice to the Public
- Wet rice noodles or like products, especially those that are loosely packed, are recommended to be consumed within the day of purchasing or stored under refrigeration.
- If there are leftover wet rice noodles or like products from a meal, they should be refrigerated as soon as possible or discarded.
- Discard wet rice noodles or like products and soaked mushrooms that smell or taste abnormal.