INTERNATIONAL FOOD SAFETY CONSULTANCY
DR WILLEM MARSMAN
Bacteria are everywhere – in the soil, water, dust and even our bodies. They cannot be eliminated totally.
Not all bacteria are harmful. For examples, some help to make cheese and yoghurt.
Bacteria need warmth, food, moisture and time to multiply.
Food poisoning bacteria grow best between 5-63°C.
Most bacteria are killed at temperatures of 70°C; and bacteria do not grow or grow on slowly below 5°C. At very low temperatures some bacteria will die, but many survive and grow again if warm conditions return.
Food poisoning bacteria can be dangerous and can kill – although this is rare.
The symptoms of food poisoning can last for days and include abdominal pains, diarrhoea, vomiting, nausea and fever. The symptoms usually come on suddenly, but can occur days after eating contaminated food.
Food poisoning bacteria are very hard to detect; they do not usually affect the taste or smell of the food.
Young children, the elderly, the sick and pregnant women are particularly vulnerable to food poisoning.
Use the links below to discover more about some of the causes of food poisoning:
Source: Salmonella has been found in raw meat, poultry and eggs, raw unwashed vegetables, unpasteurised dairy products and many other types of food. It is found in the gut and excreta of animals and humans.
Characteristics: Salmonella remains dormant when refrigerated but is destroyed by thorough cooking and pasteurisation.
Usually large numbers of the bacteria are needed to cause infection but outbreaks have been reported where the infective dose has been low.
Symptoms: The incubation period for Salmonella food poisoning is between 12 and 72 hours.
Symptoms include fever, diarrhoea, vomiting and abdominal pain.
Infection is usually mild, although it can on occasion be very severe and on rare occasions may be fatal.
Symptoms may last up to seven days.
Source: Campylobacter can be found in raw meat, poultry and excreta, untreated water and raw milk.
Milk can be contaminated by birds pecking bottle tops on the doorstep.
Pets with diarrhoea can be a source of infection.
Characteristics: The infective dose can be low.
Thorough cooking and pasteurisation will destroy Campylobacter.
Symptoms: Symptoms include a period of fever, headache and dizziness for a few hours, followed by severe abdominal pain and diarrhoea which may be bloody.
Symptoms can take 1-11 days to appear and last between two and seven days and can recur over a number of weeks.
Source: Staphylococcus aureus may be found on skin, in cuts and in the nose. It may also be found in unpasteurised milk.
It can be transferred to food from the hands or from droplets from the nose or mouth.
Characteristics: Food poisoning from Staphylococcus aureus follows the consumption of heavily contaminated food, where bacteria have multiplied and produced a toxin which causes illness when the food is consumed.
Staphylococcus aureus is dormant when refrigerated. The bacterium is destroyed by pasteurisation and normal cooking, however, the toxin may not be destroyed.
Symptoms: Onset of symptoms varies between 1-7 hours.
Symptoms are severe vomiting, abdominal pains, lower than normal termperature and occasionally diarrhoea.
Source: Bacillus cereus is found in soil and in dust.
The main source of Bacillus cereus are contaminated cooked foods subjected to inadequate post-cooking temperature control during cooling and storage.
It is frequently found in rice dishes, occasionally pasta, meat or vegetable dishes, dairy products, soups, sauces and sweet pastry products.
Characteristics: Bacillus cereus can form spores when conditions are unfavourable for growth.
The spores are not easily destroyed by heat and will survive cooking. If the food is cooled slowly or kept warm for some time before serving they will germinate producing bacteria which multiply rapidly at these temperatures and produce a very heat resistant toxin which will not be destroyed by subsequent heating.
Symptoms: The incubation period for Bacillus cereus food poisoning is between 1 to 5 hours.
Symptoms include nausea, vomiting, diarrhoea and abdominal pain.
Onset of symptoms can be very sudden, but it is usually over fairly quickly. It is unlikely to be fatal.
Source: Listeria is an environmental organism and can be found in soil, vegetation, raw milk, meat, poultry, cheeses (particularly soft-ripened varieties) and salad vegetables. One type is Listeria monocytogenes.
It is found in the gut of animals and humans, in sewage and throughout the environment.
Characteristics: Listeria, unlike most other food poisoning bacteria, can grow at low temperatures even in the fridge.
Proper/thorough cooking and pasteurisation will destroy Listeria.
Symptoms: Onset of symptoms can be from 3 to 70 days.
Symptoms range from mild flu-like illness to meningitis, septicaemia and, in pregnant women, abortion, miscarriage or birth of an infected child.
As well as pregnant women other susceptible groups are those whose immune systems are compromised, the very young and the very old.
Source: SRSVs are the commonest foodborne viral infection and are usually spread person to person.
Characteristics: SRSVs are transmitted person to person via the faecal-oral route, from aerosols caused by projectile vomit, environmental contamination eg toilets and contaminated water and food (especially bivalve molluscs).
Outbreaks occur most frequently in nursing homes and hospitals due to person to person spread.
Symptoms: SRSvs cause an acute self-limiting gastro-enteritis and are the commonest cause of epidemic viral gastro-enteritis.
Symptoms include vomiting and diarrhoea.
The incubation period is 24-48 hours and infectivity lasts for 48 hours after the resolution of symptoms.
Source: E Coli is a widespread organism and there are many different types. It is normally found in the bowels of animals and humans.
One uncommon type which can cause serious illness is Verocytotoxin producing E coli 0157 which has been found in raw and under-cooked meats, unpasteurised milk and dairy products, raw vegetables and unpasteurised apple juice.
Characteristics: The infective dose is low and a small number of organisms can cause this illness.
It can survive refrigeration and freezer storage but thorough cooking and pasteurisation will kill these bacteria. Mince, sausages, burgers and poultry should be cooked until they are piping hot throughout, the juices run clear and not pink bits remain.
Symptoms: The incubation period is 1-6 days.
Symptoms include diarrhoea, which may be bloody, and can leads to kidney failure, and in some cases death.
The very young (under 6) and elderly are particularly vulnerable.
Source: Clostridium perfringens can be found in soil, excreta, raw meat and insects.
Characteristics: Clostridium perfringens can multiply during slow low temperature cooking, warming up or long cooling periods, and is particularly associated with gravies, cooked meat dishes, stews and pies and very large joints of meat and poultry.
Clostridium perfringens produce spores which may be killed during cooking and reheating. Food that is not to be eaten immediately following cooking must be cooled rapidly then refrigerated to prevent the spores germinating.
Symptoms: Symptoms are mainly abdominal pain, diarrhoea and nausea after an 8-22 incubation period.