Bacteria – the silent killers in food

Most of us have at some time or the other eaten something that made us feel uneasy. This miserable condition often goes by the name of food poisoning. Mostly bacteria causes food poisoning.

Food Poisoning

Food poisoning is a term used to express any type of disease, illness or malaffect after consuming food. The most serious type of food poisoning is bacterial food poisoning, which may be due to bacterial infection or food intoxication secreted by the bacterial cells on food. The appearance of symptoms of food poisoning depends upon quantity, type and toxicity of the toxin. The gastrointestinal symptoms typically appear after 1-6 hours whereas the neurological and haematological effects may appear after a longer time. In most cases of food-borne illness, symptoms resemble intestinal flu and may last a few hours or even several days. Symptoms can range from mild, moderate to severe and include abdominal cramps, nausea, vomiting, diarrhoea, fever and dehydration and in severe cases, even death. Like any other organism, bacteria need temperature, moisture, nutrients and time to grow. The presence or absence of oxygen, salt, sugar, acidity and the microflora in the environment are other important factors for the growth of bacteria in the gastrointestinal tract. Given appropriate conditions, one bacterium may multiply by binary fission to become four million in eight hours. Since bacteria and toxins can neither be smelt nor seen with the naked eye, the best way to ensure that food is safe is to follow principles of good food hygiene. Every year, more than 90% cases of food poisoning are caused by Clostridium botulinum, Clostridium perfringens, Staphylococcus aureus, Salmonella, Vibrio parahaemolyticus, Bacillus cereus, Listeria monocytogenes, Campylobacter jejuni, Yersinia enterocolitica and entero-pathogenic Escherichia coli. Since food-poisoning bacteria are often present on many foods, knowing the characteristics of such bacteria is essential for effectively controlling the malady. Bacteria can cause food poisoning in two different ways. Some bacteria infect the intestines, causing inflammation and problems with normal absorption of nutrients and water leading, to diarrhoea. Other bacteria produce chemicals (known as toxins) on foods that are poisonous to the human digestive system. When eaten, these chemicals can lead to nausea, vomiting, kidney failure, and even death. Generally bacteria never grow below 40°F and are destroyed by normal cooking. Let us take a look at some of these deadly pathogens.Clostridium botulinum

• Characteristics: Produces spores and requires low oxygen atmosphere. Produces a heat-sensitive toxin.
• Habitat: Soils, plants, marine sediments and fish.
• Source: Home-canned foods.
• Symptoms: Blurred vision, respiratory distress and possible death.
• Cause: Improper methods of home-processing foods.
• Temperature sensitivity: Type E and Type B can grow at 38°F. Bacteria get destroyed by cooking and boiling for 5 to 10 minutes. Heat-resistant spores can survive.

Clostridium perfringens

• Characteristics: Produces spores and prefers low oxygen atmosphere.
• Habitat: Dust, soil and gastrointestinal tracts of animals and man.
• Source: Meat and poultry dishes, sauces and gravies.
• Symptoms: Cramps and diarrhoea within 12 to 24 hours. No vomiting or fever.
• Cause: Improper temperature control of hot foods and recontamination.
• Temperature sensitivity: No growth below 40°F. Normal cooking kills bacteria but heat-stable spores can survive.

Staphylococcus aureus

• Characteristics: Produces a heat-stable toxin.
• Habitat: Nose and throat of 30 to 50 percent of healthy population, sometimes skin and superficial wounds.
• Source: Meat and seafood salads, sandwich spreads and high salt foods.
• Symptoms: Nausea, vomiting and diarrhoea within 4 to 6 hours of infection. No fever.
• Cause: Poor personal hygiene and subsequent temperature abuse.
• Temperature sensitivity: No growth below 40°F. Can be destroyed by normal cooking but toxin is heat-stable.

Salmonella

• Characteristics: Produces an intestinal infection.
• Habitat: Intestinal tracts of animals and human beings.
• Source: High protein foods – meat, poultry, fish and eggs.
• Symptoms: Diarrhoea, nausea, chills, vomiting and fever within 12 to 24 hours of infection.
• Cause: Contamination of ready-to-eat foods, insufficient cooking and contamination of cooked foods.
• Temperature sensitivity: No growth below 40°F. Can be destroyed by normal cooking.

Vibrio parahaemolyticus

• Characteristics: Requires salt for growth.
• Habitat: Fish and shellfish.
• Source: Raw and cooked seafood.
• Symptoms: Diarrhoea, cramps, vomiting, headache and fever within 12 to 24 hours.
• Cause: Recontamination of cooked foods or eating raw seafood.
• Temperature sensitivity: No growth below 40°F. Bacteria killed by normal cooking.

Bacillus cereus

• Characteristics: Produces spores and grows in normal oxygen atmosphere.
• Habitat: Soil, dust and spices.
• Source: Starchy food.
• Symptoms: Mild case of diarrhoea and some nausea within 12 to 24 hours.
• Cause: Improper holding and storage temperatures after cooking.
• Temperature sensitivity: No growth below 40°F. Bacteria killed by normal cooking, but heat-resistant spores can survive.

Listeria monocytogenes

• Characteristics: Survives in adverse conditions for long time periods.
• Habitat: Soil, vegetation and water. Can survive for long periods in soil and plant materials.
• Source: Milk, soft cheeses, vegetables fertilized with manure.
• Symptoms: Mimics meningitis. Immuno-compromised individuals are more susceptible.
• Cause: Contaminated raw products.
• Temperature sensitivity: Grows at very low (38-40°F) temperatures. May survive at minimum pasteurization temperatures (161°F for 15 seconds).

Campylobacter jejuni

• Characteristics: Oxygen sensitive, does not grow below 86°F.
• Habitat: Animal reservoirs and foods of animal origin.
• Source: Meat, poultry, milk, and mushrooms.
• Symptoms: Diarrhoea, abdominal cramps and nausea.
• Cause: Improper pasteurization or cooking, cross-contamination.
• Temperature sensitivity: Sensitive to drying or freezing. Survives in milk and water at 39°F for several weeks.

Yersinia enterocolitica

• Characteristics: Not frequent cause of human infection.
• Habitat: Poultry, beef, swine. Isolated only in human pathogen.
• Source: Milk, tofu, and pork.
• Symptoms: Diarrhoea, abdominal pain, vomiting. Mimics appendicitis.
• Cause: Improper cooking. Cross-contamination.
• Temperature sensitivity: Grows at very low temperatures (35-40°F); sensitive to heat (122°F).

Enteropathogenic E. coli

• Characteristics: Can produce toxins that are heat stable and others that are heat sensitive.
• Habitat: Faeces of infected humans.
• Source: Meat and cheeses.
• Symptoms: Diarrhoea, abdominal cramps, no fever.
• Cause: Inadequate cooking. Recontamination of cooked products.
• Temperature sensitivity: Organisms can be controlled by heating. Can grow at freezing temperatures.

Reducing Risk

Food-borne illness is an ever-present threat that can be prevented with proper care and handling of food products. Some people are at greater risk for bacterial infections because of their age or immune status. Young children, pregnant women, foetus, the elderly, and people with lowered immunity are at greater risk. Patients with gastrointestinal problems too are at high risk of getting food poisoning. Poor personal hygiene, improper cleaning of storage and preparation areas and unclean utensils cause contamination of raw and cooked foods. Mishandling of raw and cooked foods allows bacteria to grow. Proper storage of food is an important part of reducing the risk of food poisoning. Foods must be stored in the refrigerator and eaten within a short period of time. Precautions should include adequate cooking and avoidance of recontamination of cooked food by contaminated equipment and water. Wash hands, food preparation surfaces and utensils thoroughly before and after handling raw foods to prevent recontamination of cooked foods. While reusing the refrigerated food, one should heat it properly, because simply warming at temperature not very high (20°C- 45°C) activates the spores that start reproducing.

Diagnosis

Diagnosis is based on the symptoms of food poisoning. The symptoms from the most common types of food poisoning generally start within 2 to 6 hours of eating the infected food. This time may be longer (even a number of days) or shorter, depending oh the toxin or organism responsible for the food poisoning. The doctor may be able to diagnose the food-borne illness from a list of what you’ve recently eaten and from results of laboratory tests. Diagnostic tests for food-borne illness include examination of the faeces. A sample of the suspected food if available can also be tested for bacteria and their toxins. Less common but much more serious symptoms include: respiratory distress, including the need for support on a breathing machine, kidney problems, bleeding disorders, arthritis, and nervous system disorders.

Treatment

One can usually recover from the most common, types of food poisoning within a couple of days. Most cases borne illness are mild and can be treated by increasing fluid intake, either orally or intravenously, to replace lost fluids and electrolytes. In cases with gastrointestinal or neurological symptoms, people should seek medical attention. In the most severe situations, the patient may need hospitalization in order to receive supportive nutritional and medical therapy. Dehydration is the most common complication. This can occur from any of the causes of food poisoning. Maintaining adequate, fluid and electrolyte balance and controlling blood pressure are important. Doctors will try to minimize the impact of reduced kidney function.