This page covers the major foodborne pathogens, their sources, the foods most associated with each, the mechanisms of disease, detection methods, control measures, and the regulatory frameworks that govern food safety in major markets. It gives you the practical knowledge to identify which pathogen is most likely responsible for a foodborne illness outbreak based on the foods involved and the clinical presentation, and to understand which critical control points prevent each one.
Salmonella: The Most Common Notified Foodborne Pathogen
Salmonella enterica encompasses over 2,500 serovars, of which a small number account for the vast majority of human foodborne illness. In most high-income countries, Salmonella Enteritidis (associated with eggs and poultry) and Salmonella Typhimurium (associated with a broader range of animal products) are the dominant serovars. Globally, non-typhoidal Salmonella causes an estimated 93 million cases of gastroenteritis and 155,000 deaths per year.
Salmonella invades the small intestinal epithelium using a type III secretion system that injects bacterial proteins into host cells, triggering bacterial uptake. The resulting gastroenteritis (nausea, vomiting, diarrhoea, abdominal cramps, fever) typically begins 6 to 48 hours after ingestion and lasts 4 to 7 days. The infective dose is relatively low: 100 to 1,000 organisms can cause illness, meaning even minor contamination events are clinically significant.
Control measures: adequate cooking (internal temperature above 74 degrees Celsius destroys Salmonella), preventing cross-contamination between raw poultry/eggs and ready-to-eat foods, adequate refrigeration to prevent growth (Salmonella grows between 5 and 46 degrees Celsius, optimal at 37 degrees Celsius), and pasteurisation of eggs and egg products. Vaccination of laying hens has substantially reduced Salmonella Enteritidis in egg-associated outbreaks in countries where it has been implemented.
Campylobacter: The Most Common Cause of Foodborne Gastroenteritis in Many Countries
Campylobacter jejuni and C. coli together cause more notified cases of foodborne illness than any other pathogen in the UK, EU, USA, and many other high-income countries. The primary source is poultry: 80 per cent or more of retail raw chicken is contaminated with Campylobacter in many countries. Other sources include unpasteurised milk, contaminated water, and contact with farm animals.
The illness (campylobacteriosis) typically begins 1 to 5 days after exposure: fever, abdominal cramps, and profuse, often bloody diarrhoea. The incubation period is longer than Salmonella because Campylobacter invades the colonic mucosa rather than the small intestine. In a small proportion of cases (1 in 1,000 to 1 in 2,000), Guillain-Barre syndrome, an acute inflammatory peripheral neuropathy, develops 2 to 4 weeks after infection, triggered by molecular mimicry between Campylobacter LOS structures and human gangliosides.
Control: thorough cooking of poultry (the most effective single intervention), separate cutting boards for raw poultry and ready-to-eat foods, hand hygiene, pasteurisation of milk. Campylobacter is more heat sensitive than most foodborne pathogens and is reliably killed by reaching 74 degrees Celsius at the food's core.
E. coli O157:H7 and Other STEC: The Potentially Fatal Complication
Shiga toxin-producing E. coli (STEC), of which serotype O157:H7 is the most studied, is responsible for severe haemorrhagic colitis and haemolytic uraemic syndrome (HUS). HUS, the triad of microangiopathic haemolytic anaemia, thrombocytopaenia, and acute kidney injury, develops in approximately 5 to 10 per cent of STEC infections, most commonly in children under 5 and the elderly. It is the most common cause of acute renal failure in children in many countries.
The infective dose is extremely low: fewer than 100 organisms can cause illness. Primary reservoirs are ruminants, especially cattle. Key food vehicles: undercooked ground beef (mince), unpasteurised milk and juices, raw leafy vegetables (contaminated through irrigation or run-off from cattle farms), and recreational or drinking water contaminated with bovine faecal matter.
The most important clinical point: antibiotics should NOT be given for confirmed or suspected STEC infection. Evidence suggests that antibiotics trigger the SOS response in STEC, massively increasing Shiga toxin production and dramatically increasing the risk of HUS. Supportive care is the treatment.
Listeria monocytogenes: The Slow-Growing Cold-Tolerant Pathogen
Listeria monocytogenes is unusual among foodborne pathogens because it grows at refrigeration temperatures (even at 1 to 2 degrees Celsius), meaning refrigeration does not prevent growth the way it does for most other pathogens. It is also unusually resistant to acid and salt, allowing growth on cured and fermented products.
Listeriosis has a very low incidence (approximately 0.3 to 0.6 cases per 100,000 population per year in high-income countries) but a very high case fatality rate (20 to 30 per cent). The disease is serious only in high-risk groups: pregnant women (where it can cause miscarriage, stillbirth, or neonatal infection), neonates, the elderly, and the immunocompromised. For healthy immunocompetent adults, ingestion of Listeria typically causes mild or no symptoms.
High-risk foods: ready-to-eat deli meats and charcuterie, soft cheeses made from unpasteurised milk, smoked fish products, pre-packaged salads, and any ready-to-eat food stored refrigerated for extended periods. Because Listeria grows in refrigerated food, the HACCP critical control point is not storage temperature (although keeping temperatures as low as possible slows growth) but rather shelf-life and end-point cooking or pasteurisation.
Bacillus cereus and Staphylococcus aureus: The Rapid-Onset Toxin-Mediated Syndromes
Both organisms cause illness through pre-formed toxins in food rather than through infection and colonisation of the gut. This means the illness begins much faster than with invasive organisms (1 to 6 hours for emetic B. cereus and S. aureus toxin, compared to 6 to 48 hours for Salmonella).
Staphylococcus aureus produces heat-stable enterotoxins that are not destroyed by reheating food. If S. aureus grew in food (because the food was left at room temperature for several hours) and produced toxin, cooking or reheating the food will not prevent illness even if it kills all the bacteria. The illness is a rapid-onset vomiting syndrome with minimal diarrhoea, lasting 24 to 48 hours.
Bacillus cereus has two distinct toxin syndromes: the emetic syndrome (caused by cereulide toxin, preformed in food, associated with cooked rice and starchy foods, rapid onset) and the diarrhoeal syndrome (caused by enterotoxins produced in the gut, associated with cooked meat and vegetables, onset 8 to 16 hours).
Control: prevent growth by not leaving cooked food at room temperature for more than 2 hours. Cool hot food rapidly to refrigeration temperature. Do not leave food in the temperature danger zone (5 to 63 degrees Celsius) for extended periods.
HACCP: The Seven Principles of Prevention
The Hazard Analysis and Critical Control Points (HACCP) system is the international standard framework for preventing foodborne illness in food production. It identifies biological, chemical, and physical hazards in a food production process and establishes Critical Control Points (CCPs): specific steps where control can be applied to prevent, eliminate, or reduce the hazard to an acceptable level.
The seven HACCP principles: (1) Conduct a hazard analysis identifying all potential hazards. (2) Identify the Critical Control Points. (3) Establish critical limits for each CCP (for example, minimum cooking temperature and time). (4) Establish a monitoring system for each CCP. (5) Establish corrective actions when monitoring shows a CCP is not in control. (6) Establish verification procedures to confirm the system is working. (7) Establish documentation and record-keeping.
For most food products, the primary CCPs are cooking (heat treatment to achieve a lethal reduction in pathogen numbers) and temperature control (preventing growth in storage and distribution). These two CCPs, properly controlled and monitored, prevent the majority of foodborne illness.
Frequently Asked Questions
What are the most common foodborne pathogens globally?
According to WHO estimates, the five most common agents of foodborne illness globally are norovirus, Campylobacter species, non-typhoidal Salmonella, ETEC (enterotoxigenic E. coli), and Staphylococcus aureus (toxin). In terms of mortality, non-typhoidal Salmonella, Campylobacter, and ETEC cause the most deaths globally.
What is the temperature danger zone?
The temperature danger zone is the range between 5 and 63 degrees Celsius in which most foodborne pathogens can grow. Keeping food either below 5 degrees Celsius (refrigeration) or above 63 degrees Celsius (hot holding) prevents bacterial growth. Food should not be left in the danger zone for more than 2 hours total.
What is the infective dose for E. coli O157?
The infective dose for E. coli O157:H7 is fewer than 100 organisms, making it one of the most infectious foodborne pathogens. This extremely low infective dose explains why person-to-person transmission occurs readily and why even small amounts of contaminated food or water can cause large outbreaks.
Why should antibiotics not be given for E. coli O157 infection?
Antibiotics trigger the SOS response in STEC, which dramatically increases Shiga toxin production and has been associated with increased risk of haemolytic uraemic syndrome (HUS) in observational studies. Current guidelines recommend supportive care (fluid management, careful monitoring for HUS) rather than antibiotics for confirmed or suspected STEC infection.
What foods are highest risk for Listeria?
Ready-to-eat deli meats, unpasteurised soft cheeses, smoked fish, pre-packed salads, and raw sprouts are the highest risk foods for Listeria monocytogenes. These foods are consumed without further cooking (the kill step), and Listeria grows during refrigerated storage, so even properly refrigerated foods can develop significant Listeria counts over their shelf life.
What is haemolytic uraemic syndrome (HUS)?
HUS is a serious complication of STEC infection characterised by the triad of microangiopathic haemolytic anaemia (red blood cell destruction), thrombocytopaenia (platelet destruction), and acute kidney injury (from toxin-mediated damage to renal endothelial cells). It develops approximately 5 to 10 days after the onset of diarrhoea, typically as the diarrhoea is improving. HUS is most common and most severe in young children and the elderly.
What is HACCP?
Hazard Analysis and Critical Control Points (HACCP) is the internationally recognised preventive food safety management system. It identifies potential biological, chemical, and physical hazards in a food production process and establishes specific control points where those hazards can be prevented, eliminated, or reduced to safe levels. It is required by law for food manufacturers in the EU, UK, USA, and many other countries.
What is Guillain-Barre syndrome and which foodborne pathogen causes it?
Guillain-Barre syndrome (GBS) is an acute autoimmune peripheral neuropathy that can cause progressive ascending paralysis, potentially requiring mechanical ventilation. Campylobacter jejuni is the most commonly identified trigger of GBS, responsible for approximately 30 per cent of cases. The mechanism is molecular mimicry: antibodies produced against Campylobacter LOS (lipooligosaccharide) cross-react with gangliosides on peripheral nerve myelin sheaths, causing demyelination.
What is the difference between food infection and food intoxication?
Food infection requires ingestion of live organisms that then multiply in the gastrointestinal tract and cause disease through invasion or in situ toxin production (for example, Salmonella, Campylobacter, E. coli O157). Food intoxication results from ingestion of pre-formed toxins in food: the organism may or may not still be present, but the toxin is what causes illness. Examples include Staphylococcus aureus enterotoxin and Bacillus cereus cereulide. Intoxication typically has a shorter incubation period (1 to 6 hours) than infection (6 to 72 hours).
What is the role of biofilm in food safety?
Biofilms form when foodborne pathogens such as Listeria, Salmonella, and E. coli attach to food contact surfaces (conveyor belts, cutting equipment, drains, refrigerated storage units) and produce a protective extracellular polysaccharide matrix. Bacteria within biofilms are highly resistant to cleaning and disinfection. A single biofilm on a food contact surface can contaminate thousands of food products before it is detected. Effective cleaning and disinfection protocols in food manufacturing must be validated to ensure they are genuinely removing biofilm from critical surfaces.