Food is often contaminated with pathogens such as bacteria, viruses, protozoa and parasites, leading to a host of foodborne illnesses. In order to cause health problems, pathogens must display characteristics such as the ability to withstand stomach acid, resistance to digestive enzymes, and the ability to compete with pre-existing gut microflora. If they meet these criteria, infection may result in symptoms varying from gastrointestinal to neurological effects. These normally present between 8 hours to a few days once the number of organisms ingested exceeds the minimum infective dose (MID). Two of the most common symptoms of foodborne infection are vomiting and diarrhea.


Vomiting (or emesis) occurs when vomiting receptor sites located along the GI tract (mainly in the duodenum) are activated. These sites may be activated due to distention of the small intestine if you over eat, or inflammation of the GI tract caused by microorganisms or their toxins. When the vomiting receptors are activated, nerves send signal directly to the vomiting center in the brain or to the nearby chemoreceptor trigger zone (ctz), causing vomiting. This action is associated with a relaxing of the lower esophageal sphincter, contraction of the diaphragm and abdominal muscle, increased peristalsis, and closure of the epiglottis.


diarrhea is an increased frequency of watery stool three or more times a day lasting 1 or more days. It may occur when. This is when bacteria causing the infection produces toxins that interferes with electrolyte channels lining the GI tract causing them to leach into the lumen of the GI tract. This movement of electrolytes results in water also being pulled into the lumen. The excess fluid is subsequently lost in the stool. Inflammation and damage to the GI walls caused by bacteria and other microorganisms may also cause this “leaky” effect. Some pathogens may cause extensive tissue damage resulting in bloody diarrhea.

Apart from vomiting and diarrhea, patients suffering from foodborne infection may also present with fever, chills, fatigue, malaise, bloating, loss of appetite, sweating stomach cramps, and headache. Complications may result in dehydration, anemia, malabsorption of nutrients, and septicemia (blood infection).

Foodborne infection may be caused by either invasive or noninvasive organisms. Invasive organisms are those that are able to penetrate the tissue of the GI tract, entering the blood stream and reaching other organs where they cause further damage. Noninvasive organisms do not penetrate tissues nor multiply in cells but instead stick to the surface of the GI tract where they colonize and produce toxins which cause inflammation and damage to the GI wall.

Defense Mechanisms Against Foodborne Infections

Luckily we have a number of defenses against foodborne pathogens. Hence every infection will not lead to illness. One defense obviously is our white blood cells. For example, phagocytic leukocytes can engulf, digest and destroy pathogens using enzymes, hydrogen peroxide and free radical compounds. In addition, antibodies, bind and destroy pathogens. Other defenses include:

  • The intestinal mucosa which acts as a physical barrier
  • Competing microflora in the GI which competes for nutrients, and produce inhibitory substances to prevent other microorganisms from growing
  • Bile salts which inhibits microbial growth
  • The constant movement of the intestine which helps to reduce the attachment and colonization of new bacteria
  • Fiber in the diet, which helps to bind and eliminate microorganisms.

Reference: Taylor, S. L. (2017). Disease processes in foodborne illness. In C. E. R. Dodd et al. (Eds.), Foodborne diseases (3rd ed.). Philadelphia, PA: J.B. Lippincott.  

Courtney Simons
Courtney Simons is a food science professor. He holds a BS degree in food science and a Ph.D. in cereal science from North Dakota State University.
Courtney Simons on FacebookCourtney Simons on Linkedin