Information provided in this section is in the public domain and is provided by US Food and Drug Administration (FDA); US Department of Agriculture (USDA), Food Safety and Inspection Service (FSIS); the Centers for Disease Control and Prevention (CDC); National Institute of Diabetes and Digestive and Kidney Diseases (NIDDKD); and Canadian Food Inspection Agency (CFIA).
Bacteria are the largest group of problematic foodborne pathogens by far. They are small, one-celled microbes that come in many shapes and are capable of reproducing themselves. Typical cell shapes include spherical (cocci), rod-shaped (bacilli), and curved or comma-shaped (spirillar). These shapes can be seen under the microscope when the bacteria are stained in the laboratory with a Gram stain or dye. Whether or not bacterial cells stain Gram-positive (retaining a crystal violet color) or Gram-negative (those losing the color) also aids in identifying what bacteria are present and what treatments to administer. An important substructure of bacteria is the flagella, a hair-like tail that is responsible for bacterial movement. Bacteria are also classified and identified on the basis of their flagella. Much of modern foodborne microbiology is devoted to keeping pathogenic bacteria out of food products and preventing their growth if they are present. Salmonella, E. coli O157:H7, Listeria, and Shigella are well known species of foodborne bacteria.
Viruses are thought to be the leading cause of foodborne illness in the United States based on the percentage of people ill, even though there are only a few viruses that are important foodborne pathogens. Viruses are much smaller than bacteria and cannot live outside a host, such as an animal or the human body. They are not cells but look more like particles (they have a protein coat, not a cell wall); reproducing only when they invade living cells. Although they do not multiply in food products, it can take only a few viral particles to make a person sick. Viruses are easily transferred from one food product to another, from contaminated water to foods, and from infected food handlers to foods. The two most well-known foodborne viruses are Hepatitis A and Norovirus (also known as Norwalk virus). Antibiotic drugs will not help in treatment because antibiotics fight against bacteria not viruses.
There are about 20 different species of that are known to cause illness in humans from contaminated food or water. They range in size from microscopic single-celled organisms known as protozoa to visible worms known as helminthes. But, what they all have in common is that they derive their nourishment from other living organisms known as host organisms. When the parasites live and reproduce in the tissues and organs of animal and human hosts they can then be excreted in feces and go on to infect other individuals. There is a hard shell covering to some varieties of protozoa that permit them to survive for lengthy periods of time in water waiting to infect another host. Examples of protozoan parasites include Cyclospora, Giardia, and Cryptosporidium. A well-known foodborne helminth is Trichinella, an intestinal roundworm.
There are several types of molds (fungi) that are foodborne pathogens, and algae found in plankton can cause paralytic shellfish poisoning. Several other types of toxins found in seafood can also cause illness. Mad Cow Disease, also known as Bovine Spongiform Encephalopathy (BSE), is a degenerative brain disease of cattle caused by prion particles that can be passed to humans who consume beef contaminated by the brain, spinal cord, or nervous tissue of diseased animals. Heavy-metal contamination and synthetic plastics such as melamine have also been found in recent years to cause human illness and is the subject of ongoing research.
Some microorganisms can cause big health problems when consumed in contaminated foods or beverages. The world of foodborne microbes contains a mix of approximately 250 different types of bacteria, viruses, parasites, molds, and algae that are known to cause disease in humans and are therefore called foodborne pathogens. What they all have in common is that they are most often too small to be seen without a microscope, they have simpler structures and functions than higher plants and animals, and they are able to be cultured in laboratory settings with prescribed methods that aid in their identification.
The term foodborne pathogen loosely describes the microbes that are found in animals (in farm/zoo animals and pets) and in the environment (soil, water and air) that make people sick regardless of how they became infected. Usually, infection happens by direct ingestion of a contaminated product, but it can also happen by contact with other individuals or contact with an animal or pet. Some foodborne microbes make people ill by forming toxins in foods that affect the gut or the neurological system. When an illness is caused by a ingesting a toxin and causes an intoxication it will generally make people sick faster than other foodborne pathogens which cause an infection.