And yeast, another type of fungus, is a necessary ingredient in most types of bread. Other fungi can cause illness. One example is candida — a yeast that can cause infection.

Candida can cause thrush — an infection of the mouth and throat — in infants and in people taking antibiotics or who have an impaired immune system. Fungi are also responsible for skin conditions such as athlete's foot and ringworm.

Protozoans are single-celled organisms that behave like tiny animals — hunting and gathering other microbes for food. Many protozoans live in your intestinal tract and are harmless. Others cause diseases, such as:. Protozoans often spend part of their life cycles outside of humans or other hosts, living in food, soil, water or insects.

Some protozoans invade your body through the food you eat or the water you drink. Others, such as the malaria protozoans, invade your body through mosquito bites.

Helminths are among the larger parasites. The word "helminth" comes from the Greek word for worm. If these parasites — or their eggs — enter your body, they settle in your intestinal tract, lungs, liver, skin or brain, where they live off your body's nutrients.

Helminths include tapeworms and roundworms. There's a difference between infection and disease. Infection, often the first step, occurs when bacteria, viruses or other microbes that cause disease enter your body and begin to multiply.

Disease occurs when the cells in your body are damaged — as a result of the infection — and signs and symptoms of an illness appear. In response to infection, your immune system springs into action.

An army of white blood cells, antibodies and other mechanisms goes to work to rid your body of whatever is causing the infection. For instance, in fighting off the common cold, your body might react with fever, coughing and sneezing. What's the best way to stay disease-free?

Prevent infections. You can prevent many infections and avoid spreading infections through simple tactics such as these:. Your health care provider can perform diagnostic tests to find out whether you're infected, how serious the infection is and how best to treat that infection.

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By Mayo Clinic Staff. Enlarge image Types of infectious agents Close. Types of infectious agents Infectious agents come in many shapes and sizes. Thank you for subscribing! Sorry something went wrong with your subscription Please, try again in a couple of minutes Retry.

Show references Overview of bacteria. Merck Manual Professional Version. Accessed Sept. Levinson W, et al. Bacteria compared with other microorganisms. In: Review of Medical Microbiology and Immunology: A Guide to Clinical Infectious Diseases. McGraw-Hill Education; National Institute of Allergy and Infectious Diseases.

Kimberlin DW, et al. Red Book Online. American Academy of Pediatrics; Goering RV, et al. Mims' Medical Microbiology and Immunology. Elsevier; Nonpharmaceutical interventions NPIs. At home: Flu prevention. Centers for Disease Control and Prevention. Food and water safety. Common questions about vaccines.

IBM Micromedex. Preventive steps. coli cells alive. Disrupting this regulation, said Mi, would be an effective way to kill bacteria. Fred Mamoun: fred. mamoun yale. edu , Share this with Facebook Share this with X Share this with LinkedIn Share this with Email Print this.

To answer that question, he and his postdoctoral associate Sheng Shu turned to E. Media Contact Fred Mamoun: fred. More News. Ehud Mendel named the Nixdorff-German Professor of Neurosurgery.