In this approach bacteria are grouped into genera and species on the basis of the following characteristics: 1) Structural and morphological characteristics including shape, size, arrangement, capsules, flagella, endospores, and Gram stain; 2) Biochemical and physiological traits such as optimum temperature and pH ranges for growth, oxygen requirements, growth factor requirements, respiration and the fermentation of end products, antibiotic sensitivities, and types of carbohydrates used as an energy sources.