Parasitism

When symbiosis confers benefit to one organism at the cost of the other (i.e., the host), the relationship is often viewed as being parasitic.[2] Many parasites, such as the parasitic protozoa Entamoeba, can persist as a common inhabitant of the gastrointestinal system. These inhabitants compete for nutrients and impair production, but seldom generate acute symptoms associated with disease. When symptoms of disease are observed, the organism is then considered to be pathogenic. Typically, pathogenic microbes are thought to be transient inhabitants, but disruption of the ecosystem can provide opportunity for indigenous microbes to overwhelm the host.

The host has several mechanisms to prevent infection of the gastrointestinal tract. Acid secretion by the stomach, intestinal motility and secretions, and the indigenous flora are deterrents to pathogen colonization. Nonetheless, microbes have adapted and evolved to overcome or, in some cases, take advantage of the preventive mechanisms. Specialized immune cells (Peyer's patch) in the intestine secrete antibodies to protect the body against toxins and potential pathogens, but some pathogenic

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Independent

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Independent

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association

Fig. 1 Vin diagram showing interrelationships of various symbioses and the relationship to the host. (Adapted from Ref. 4.) (View this art in color at www.dekker.com.)

Fig. 1 Vin diagram showing interrelationships of various symbioses and the relationship to the host. (Adapted from Ref. 4.) (View this art in color at www.dekker.com.)

bacteria can bind and invade these specialized immune cells.

Zoonotic pathogens are a problem in animal production. These microorganisms may be commonly found in animals without any apparent disease, and yet are potentially disease-causing to humans. Salmonella, Campylobacteria, Shigella, Enterococcus, and the Esche-richia coli Shiga toxin-producing strains are all potential pathogens to humans and are commonly associated with animal waste.[3] As a result, potential for fecal adulteration of meats and the possible contamination of water and food supplies from land application of animal waste are burdening issues of food safety and animal production.

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