Infections Caused by Bacteria

Bacteria are microscopic, single-celled organisms. Millions of different kinds of bacteria live throughout the world. Some live in the environment, and others live on the skin, in the airways, in the mouth, and in the digestive and urinary tracts of animals and p

A healthy animal lives in harmony with many microorganisms that establish themselves on or in the body. The microorganisms that usually live on or in a particular body site are called the resident flora (or microbiota). The resident flora at each site include sev

Several steps help protect animals against infection. Sometimes, antibiotics are administered to prevent an infection from developing. This preventive measure is called prophylaxis. Many healthy animals that undergo certain types of surgery, such as intestinal su

Many diseases, drugs, and other treatments can cause the body’s natural defenses to break down. Such a breakdown can lead to infections, even by microorganisms that normally live harmlessly on or in the body. For example, the risk of infection is greatly increase

Infectious diseases are usually caused by microorganisms that invade the body and multiply. Invasion by most microorganisms begins when they adhere to cells in the body. Whether the microorganism remains near the invasion site or spreads to other sites depends on

Physical barriers and the immune system defend an animal’s body against organisms that can cause disease. Physical barriers include outer coverings, such as skin, fur, feathers, and scales. Additional barriers include the mucous membranes, tears, ear wax, mucus,

Microorganisms are tiny living creatures, such as bacteria, fungi, and viruses. Microorganisms are present everywhere. Despite their overwhelming abundance, relatively few of the hundreds of thousands of species of microorganisms invade, multiply, and cause illne

Viruses are much smaller than fungi or bacteria, and they must invade a living cell to reproduce, or replicate. The virus attaches to a cell, enters it, and releases its DNA or RNA inside the cell. The DNA or RNA of the virus is its genetic information, which tak

A parasite is an organism that lives on or in another organism (usually referred to as the host), causing harm to the host. Parasites enter the body most often through the mouth or skin. Parasites that enter through the mouth are swallowed and can either remain

Fungi are a type of organism that can infect animals and people. Yeasts, molds, and mushrooms are all examples of fungi.