These are some of the interesting names for small microbes that can cause big health problems when consumed in contaminated foods or beverages. The world of foodborne microbes (microorganisms) 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.
The largest group of problematic foodborne pathogens by far is bacteria. They are small, one-celled microbes that come in many shapes and are capable of reproducing themselves. Typical shapes include spherical cells known as cocci, rod-shaped cells known as bacilli, and curved or comma-shaped cells known as 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, Escherichia coli O157:H7, Listeria, and Shigella are well known species of foodborne bacteria.
Although there are only a few viruses that are important foodborne pathogens, they are now thought to be the leading cause of foodborne illness in the United States based on the percentage of people ill. 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).
There are about 20 different species of parasites 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 helminths. 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 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 are the subject of ongoing research.