The Nature of Bacterial Host-Parasite Relationships in Humans

The Nature of Bacterial Host-Parasite Relationships in Humans

Dr.kareema Amine Al-Khafaji Assistant professor in microbiology, and dermatologist Babylon University , College of Medicine , Department of Microbiology.
Bacteria are consistently associated with the body surfaces of animals. There are many more bacterial cells on the surface of a human (including the gastrointestinal tract) than there are human cells that make up the animal. The bacteria and other microbes that are consistently associated with an animal are called the normal flora, of the animal. These bacteria have a full range of symbiotic interactions with their animal hosts. In biology, symbiosis is defined as "life together", i.e., that two organisms live in an association with one another. Thus, there are at least three types of relationships based on the quality of the relationship for each member of the symbiotic association.

Types of Symbiotic Associations
1. Mutualism. Both members of the association benefit. For humans, one classic mutualistic association is that of the lactic acid bacteria that live on the vaginal epithelium of a woman. The bacteria are provided habitat with a constant temperature and supply of nutrients (glycogen) in exchange for the production of lactic acid, which protects the vagina from colonization and disease caused by yeast and other potentially harmful microbes.
2. Commensalism. There is no apparent benefit or harm to either member of the association.
3. Parasitism. In biology, the term parasite refers to an organism that grows, feeds and is sheltered on or in a different organism while contributing nothing to the survival of its host. In microbiology, the mode of existence of a parasite implies that the parasite is capable of causing damage to the host. This type of a symbiotic association draws our attention because a parasite may become pathogenic if the damage to the host results in disease.