A pathogenic organism is a bacterium, fungus, prion or virus that survives by feeding off of a host. A pathogenic organism typically causes disease in the host organism.
Although most bacteria do not cause disease in humans, people with a suppressed immune system are more susceptible to opportunistic pathogens that often thrive in the warm, moist environment of the human body. The body's natural responses to invading pathogenic organisms include a rise in body temperature. Many of these natural responses inhibit the ability of these organisms to live and reproduce. To survive when confronted by antibiotics, some strains of bacteria have evolved and developed the ability to resist the most commonly prescribed forms of medication used to rid the body of these pathogens.