Campaign against ready made food, Stop ready meals and foodborne diseases |
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Bacillus cereus PROJECT
Foodborne pathogen, Bacillus cereus: growth in rice-based foods and inhibitory effects of Ocimum basilicum, Thymus vulgaris and Origanum vulgare and their essential oils.
I started this project after seeing many patients with IBS-related symptoms possibly triggered by food poisonings in the past. We all know how severe food poisonings triggered by Escherichia coli, Salmonella and Listeria monocytogenes can be.
Bacillus cereus causes in most cases only 'minor' upsets. But I believe, that even a minor food poisoning can be the cause and/or the trigger for several gastroinestinal problems/diseases.
For a wider spectrum of results on how B. cereus grows on rice, several different rice were used. Rice 6a is a long grain basmati species, which grows in the foothills of the Himalayas and has a nutty, perfumy taste. This rice was processed like other white rice by removing the bran. Rice 2 and 6b is wholegrain/brown rice, which is the original form of rice with intact bran, a natural fibre, which contains vitamins and minerals, including potassium, niacin, riboflavin, and thiamine. All other rice used in this experiment is white rice, where the bran is removed by polishing. It could not be determined if the white rice we used was fortified with minerals and vitamins.
THE RICE USED IN THIS RESEARCH
Rice 1:
Weight Watchers Chicken Tikka and Coriander Rice
Rice 2:
Waitrose-Food Doctor Thai Chicken with Sesame Seed Wholegrain Rice
Rice 3:
Sainsbury’s Chili Con Carne with Rice
Rice 4:
Marks & Spencer Chicken Balti
Rice 5a:
Chinese Take-Away with Boiled Rice
Rice 5b:
Chinese Take-Away with Egg-Fried Rice
Rice 6a:
Home Boiled White Rice
Rice 6b:
Home Boiled Wholegrain Rice
Ready meals sample dishes with wholegrain rice and white rice were purchased on three different occasions from the supermarket outlets. For comparison, home boiled rice and rice from three Chinese take-away outlets were also tested.
Fresh and dried Ocimum basilicum, Thymus vulgaris and Origanum vulgare have been obtained from markets. The fresh herbs were stored for 24h at room temperature and have been watered once with distilled water. Dried herbs were purchased in February 2007 with a “best before Jan 2009” label.
The ready meals containing the tested rice were obtained on three different occasions from different supermarket outlets. The take-away rice was obtained from three different shops and three different home-boiled rice packets have been used for the white and the wholegrain rice.
RESULTS (short version)
The Chinese take-away rice (5a and 5b) had the highest count of cfu (colony forming units)of bacteria. A stain showed also Gram positive bacteria. The ready meal with the overall highest amount of Bacillus cereus and/or other Gram positive bacteria was the Waitrose-Food Doctor Thai Chicken with Sesame Seed Wholegrain Rice.
The table - which food had the highest count -was similar whether B. cereus were added (to see how essential oils can inhibit the growth of bacteria) or not (to see a general bacterial growth).
It is difficult to establish exactly how many bacteria are necessary to cause a food poisoning! Some research show that 10,000,000 bacteria per gram of food are necessary. But when does food poisoning start and when does an 'upset stomach' stop?
Bacillus cereus is a spore-forming, Gram-positive anaerobic with large vegetative cells. It occurs naturally in most foods and grows over a temperature range of 8 to 55 C with an optimum growth around 25-37º C (within the pH range of 4.3 to 9.3). Growth and enterotoxin production in psychrotrophic strains in temperatures around 4 C are not uncommon. Bacillus cereus causes two different forms of food poisoning: the emetic illness, which is mediated by a highly stable toxin and the diarrhoeal illness, which is mediated by a heat and acid-labile enterotoxins.
Outbreaks of food poisoning due to Bacillus spp. have been described since the beginning of the century (Lund, 1990). The first confirmed outbreak of B. cereus food poisoning occurred in Norway in 1950. The food vehicle was vanilla sauce, which had been prepared a day in advance and stored at room temperature before serving. Consumption of contaminated vanilla sauce resulted in a diarrhoeal illness. The sauce was later found to contain 2.5 × 10^7 to 1.1 × 10^8 B. cereus. Four related outbreaks were described involving more than 600 people. To provide further evidence that B. cereus was the causative agent, several tests by the Norwegian microbiologist Hauge, who inoculated sterile sauce with B. cereus, incubated it for 24 hours and then consumed the sauce lead to a first recognition of B. cereus as an important cause of food poisoning worldwide (Johnson, 1984). Statistics regarding B. cereus food poisoning vary between 7.4% and up to 33% of all bacterial food-borne outbreaks. Low figures are due to constant underreporting and the mildness of the majority of cases (Crerar et al. 1996).
Francis Drobniewski (1993) states that Bacillus cereus elaborates several toxins, including a necrotizing enterotoxin, an emetic toxin, phospholipases, proteases and hemolysins. The incidence of non-food-poisoning-related infections is likely to increase because of greater recognition of B. cereus as a pathogen outside the gut. (see Fig. 3/Drobniewski Fig.1). The non-gastrointestinal diseases of B. cereus include severe keratitis, endophtalmitis, panophtalmitis and infection of wounds.
Bacillus cereus may be differentiated into 18 serotypes based upon flagellar (H) antigens. Eight of these serotypes are responsible for food-borne illness caused by this organism. Serotypes 1, 3, 4, 5, 8 and 12 have been associated with emetic illnesses, while serotypes 1, 6, 8, 9, 10, and 12 have been associated with diarrhoea (Jay, Gilbert and Parry 1997).
Bacillus cereus may be found in soil, dust and water that has run off soil. Raw food of plant origin is the major source of B. cereus (Burgess and Horwood, 2006). Most food-borne poisonings are triggered by rice, although not the spectacular ones with plenty of media attention like outbreaks of gastroenteritis and/or food poisonings triggered by Salmonella, Escherichia coli or Listeria monocytogenes. Many food poisoning cases have occurred where bulk rice is prepared in advance. Resistant spores (particularly serotype 1) may survive cooking to germinate, grow and produce emetic toxin during storage. In most cases of emetic toxin food poisoning illness occurs following ingestion of precooked food held for too long at unsatisfactory storage temperatures (Jenson and Moir, 1997).
The numbers of bacteria can double in 25 – 60 minutes in boiled rice held at 30º C. This rate is reported to be higher if protein sources such as chicken, beef or egg are present – a finding which makes ready-meals even more vulnerable to infections.
Bacillus cereus PROJECT #02
All tested rice showed the highest count of B. cereus colonies at 30º C, followed by 25º C and room temperature. 4º C can also show high counts when the strain used is psychrotrophic. Rice 5a and 5b (boiled and egg fried rice from take-away outlet) had the highest overall levels, Rice 6a and b (home cooked rice) the lowest. Commercial ready-to-eat/ready-to-reheat rice varied but consistently showed a higher count in rice 2 (Waitrose-Food Doctor Thai Marinated Chicken with Sesame Seed Wholegrain Rice).
The amount of B. cereus on rice tested in ready meals varies because of added protein sources. In rice 2, sesame seeds are an own source of possible contamination with other bacteria. (e.g. Salmonella). A cross contamination through other bacteria were not examined in this experiment.
It was also not examined, how many colonies would be necessary to trigger a food-poisoning reaction, like cramps, diarrhoea, nausea, vomiting.
The addition of herbs had a significant impact on fresh and prepared rice.
The essential water and steam distilled oils showed the highest level of inhibitory effects. Ocimum basilicum (basil) had a minor higher effect compared with Thymus vulgaris (thyme) and Origanum vulgare (oregano). A mixture of equal parts of all three oils did not increase the inhibitory effects. The higher the dosage of essential oils, the more the bacterial growth was restricted. The inhibition rate reached levels between 80 and 100% (at a level of 80 µl of essential oils).
Rice, mashed potatoes and other starchy foods as well as vegetable sprouts are the main carrier for the emetic illness triggered by Bacillus cereus. Diarrhoeal illness is not very often connected with rice, but cannot be excluded. The diarrhoeal toxin types are to be found in raw, processed and dried foods such as spices, flour, bakery products, desserts especially with custard and cream, turkey, beef, seafood, salads, noodles, sauces, soups, ready meals. The fact that it can be found in so many different food makes the bacterium so important. Rice is one of the main carriers for B. cereus and it is possible, that in countries where rice is not the staple diet, infections/toxico-infections may occur more regularly.
Because food poisoning symptoms by B. cereus are mild compared with other food-borne bacteria, there are no satisfactory epidemiology data available.
The endospores of B. cereus have a high resistance to hostile environments (heat, cold, chemical-resistant) and can survive in hot springs, arctic ice, fresh water, deserts, etc. The ability to withstand environmental stresses like cooking, freezing, high salt foods, dried or acidic foods make B. cereus an important bacterium, although its health implications are not yet properly researched and the food poisonings triggered by B. cereus are very rarely severe. The spore itself is not dangerous but once the conditions of the food are improved (addition of other ingredients, like spices, protein-rich foods, etc.), the spores turn into vegetative cells. Improper storage of food, re-heating, slow cooling processes, etc. will increase the conversion into vegetative cells, which then produce the toxin or grow to high enough numbers in the food to cause illness.
Control measures for food manufacturers and preparation outlets (e.g. take-aways) have to be increased.
Not a day goes by without new food-scares worldwide, be it a recall of pre-washed salads, ready meals, or tinned food… be it glass fragments in tortillas, plastic bits in flavouring sachets, metal pieces in garlic bread. But public policies dealing with the risk of foods are putting the burden of maintaining hygienic conditions more and more onto the individual.
There is an increased use of heat treatment of vacuum-packed foods (sous vide) or other kinds of minimal processing in restaurants and at home in the preparation of the food. Ready meals are used in hospitals and old age welfare services, which means that they are served to immuno-compromised persons. Considering that mainly small factories/companies produce these products, it is essential to ensure that the products are safe for the consumers.
We asked the question, if the addition of tasty herbs could be one way to avoid the growth of B. cereus. The answer is yes and the use of certain herbs during manufacturing and during the cooking/heating process at home or in homes would have positive health effects at low costs.
Once upon a time, ready meals, ready-to-reheat meals, take-away meals, etc. were an alternative exception for a “real meal” used rarely when in a hurry. After manufacturers and supermarkets discovered the profitability of ready meals compared with fresh food, ready meals were promoted as convenient for our busy and hectic life-style. Now, that the ready meals are part of our life, the industry does not campaign mainly because of the convenience, but is promoting ready meals as healthy options.
Here lies the real danger for public health. Many bacteria are able to survive food processing by altering their physiological makeup and increasing their tolerance. “Since some Salmonella survive the antibiotic treatment, they will also survive the treatment used in processing plants.” (Gregory Phillips from Iowa State University College). Newly resistant strains of bacteria will continue to emerge the more they can tolerate stress from heat and antibiotics. Salmonella and Listeria monocytogenes are already known as ‘the bacteria that never die’… and we have to add Bacillus cereus to the list of “survivor-bacteria”.
HOME SAFETY MEASURES:
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Ensuring adequate temperatures are reached during cooking of food mixes such as sauces, custards, and soups to inactivate the bacteria.
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Keeping cooked hot foods above 60º C (preferably 70º C) if not served immediately.
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Ensuring the rapid cooling of cooked food by dividing into smaller lots and refrigerating in shallow containers (less than 10cm deep).
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Storing cold foods at or below 4º C to prevent toxin being produced.
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Avoiding storing protein-containing foods with cooked rice because this stimulates the growth of Bacillus cereus.
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Reheating foods to 75º C or until steaming hot, as flash frying or brief rewarming/reheating is not adequate to destroy the toxin.
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Preventing cross-contamination from raw to cooked foods (by using separate preparation areas or sanitising between processes).
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Thoroughly washing fruit and vegetables with clean water of drinking standard before use. |
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