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strain:see strength of materialsstrength of materials,
measurement in engineering of the capacity of metal, wood, concrete, and other materials to withstand stress and strain. Stress is the internal force exerted by one part of an elastic body upon the adjoining part, and strain is the deformation or change in
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a pure culture of a species of microorganism in which its morphological and physiological characteristics are studied.
Strains can be isolated from a variety of sources, for example, soil, water, or food, or they can be isolated from a single source at different times. Hence, the same species of bacterium, yeast, or microscopic fungus may have a great many strains, differing from one another in several characteristics, such as sensitivity to antibiotics and capacity to produce toxins and enzymes. Commercial strains of microorganisms developed as a result of selection and used in industry for the microbiological synthesis of proteins (including enzymes), antibiotics, vitamins, and organic acids are much more productive than wild strains.