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In this article we will discuss about the Living Agents of Disease.
In nature, both non-living and living agents do exist. The relationship of the living, agents with the environment has been named “ecology” (Gr. aikos — home, native land logos — science). The living agents are distributed everywhere in the environment as well as inside and on the surface of human body.
Those living agents which produce the disease in man are called pathogenic microorganisms or “Pathogens“. Though the soil is an unfavorable habitat, most of the pathogens may survive for three days to three weeks; whereas the saprophytes (non-pathogens) live for longer period in the soil.
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The human body is the most suitable environment for the multiplication and production of disease by pathogenic microorganisms. Therefore, in dental microbiology, only the living agents of disease (Pathogens) are to be studied in detail as they are variable in their shape, size, structure and pathogenicity.
Until the eighteenth century the classification of living organisms placed all organisms into one of two kingdoms:
Plant or Animal kingdom.
But in dental microbiology, we study some organisms that are predominantly plant like, others that are animal like and that are variable in size—macroscopic to electron microscopic.
Some organisms that share characteristics common to both plants and animals are placed into a third kingdom—called Protista—to include those unicellular organisms that are typically neither plant and animals. The protists encompass bacteria, fungi and protozoa.
Viruses are not cellular organisms, therefore they are not classified as protists. Bacteria are referred to as lower protists, but others—algae, fungi and protozoa—are called higher protists.
Electron microscopy study discovered two groups of protests:
(a) One group with nucleus not bounded by nuclear membrane known as prokaryotic cells (bacteria),
(b) Other group with nucleus bounded with nuclear membrane called as eukaryotic cells (fungi, algae and protozoa).
