Microbial foodborne illness, also commonly called ‘food poisoning’, is illness caused by eating food contaminated with specific types of microorganisms or toxins formed by these microorganisms. Microorganisms that are capable of causing illness are called ‘pathogenic microorganisms’ or simply ‘pathogens’. Microorganisms that may be pathogenic are bacteria, viruses, parasites and moulds. There are many microorganisms that are not pathogenic but they can cause food to spoil (e.g. mould growth on bread). Although these spoilage microorganisms are a concern for the food industry.
In Australia, the illness most commonly caused by eating food contaminated with pathogens or their toxins is foodborne gastroenteritis. The usual symptoms include nausea, diarrhoea and/or vomiting; these generally last for less than a week. Most people have either suffered from foodborne gastroenteritis at some stage of their lives or know someone who has.
There are some long-term illnesses that may develop after patients recover from symptoms of foodborne gastroenteritis. The effects of these can last for a much longer time than the initial gastroenteritis and may even cause lifetime disability. Irritable bowel syndrome – which causes abdominal pain, discomfort, bloating and alteration of bowel habits – is one example of this type of illness.
Some pathogens can cause illnesses other than foodborne gastroenteritis or gastroenteritis associated illnesses. Examples of these are:
• flu-like symptoms
• damage to the nervous system
• damage to the liver
• damage to the kidneys
• meningitis – inflammation of the lining of the brain and spinal cord
• septicaemia – infection of the bloodstream
• encephalitis – inflammation of the brain.
Some people have a higher chance of contracting a foodborne illness than others, and they are also more likely to suffer more severely, develop more complications and, in some circumstance, die. These people are classed as ‘vulnerable persons’.
Pathogenic foodborne bacteria
There are over a dozen different types of bacteria classed as foodborne pathogens. This book focuses on those that are more likely to be an issue for food businesses based in Australia. Many bacteria exist in only one structural form, called vegetative cells. Some bacteria can also exist in another structural form called an endospore.
Bacterial cells are simple structures, consisting of a cell wall enclosing the components that the cell needs to survive and grow, such as DNA. Bacteria need to be in their cellular form to grow.
Bacteria that form spores are termed ‘spore-forming bacteria’. Spores have a thick outer layer that protects the inner contents from unfavourable conditions. For example, bacteria can survive exposure to chemicals and much higher cooking temperatures when they are in the spore form then when they are in the cell form. Although they are not capable of growing like cells, spores are able to survive for long periods of time in a dormant state. Spores can be activated to form cells again when the surrounding environment changes, such as when moisture or a new source of nutrients becomes available
How pathogenic bacteria can contaminate food
Pathogens can contaminate food either before or after it leaves the farm; that is, at any point in the ‘food chain’. Routes or sources of contamination can be grouped into seven primary categories:
• Food production animals (such as cows, pigs, sheep and poultry) – pathogenic bacteria may occur naturally in the intestines of these animals and can be spread to the surfaces of their flesh (i.e. their ‘meat’) when the animals are slaughtered and butchered.
• The environment where food is grown or harvested – pathogenic bacteria that occur naturally in soil and water may be spread to food. For example, fruit and vegetable crops can become contaminated via the soil they are grown in, or fish and shellfish can become contaminated via the water they live in.
• ‘On farm’ contamination routes involving human practices – there are many examples of these, including:
– irrigating crops with water contaminated with animal manure
– using contaminated water to dilute agricultural chemicals sprayed onto crops
– using animal manure as a crop fertiliser
– harvesting fallen fruit from orchards where animals have grazed
– poor hygiene of field workers and lack of adequate toilet facilities
– spread of contamination from one area to another via contaminated farm equipment or contaminated water run-off.
• Insects and animal pests (post harvest or slaughter) – pests that may spread contamination onto food include rats, mice, birds, cockroaches and flies. Contaminants can be spread by either direct contact or indirect transfer. An example of indirect transfer is people bringing bacteria into the premises by walking through an area fouled with bird droppings.
• Food handlers – people can carry pathogenic bacteria either as part of their normal body flora or because they have an infection, such as gastroenteritis. These pathogens may be transferred to food in a variety of ways, such as a food handler going to the toilet and not washing their hands properly before touching food.
• Spread of contamination from one food item to another, or from contaminated equipment – this is referred to as cross contamination. Inadequate cleaning and sanitation, and unhygienic practices may spread pathogens in the food processing and handling environment; for example, via poorly cleaned equipment such as meat slicers, blenders and utensils.
• Water used in food handling or processing activities – use of untreated water during processing or failure of water treatment plants can contaminate food. However, these issues are not generally a problem in Australia.