B. cereus is a facultative aerobic bacterium, endospore forming and a gram +ve bacteria. They are large organism with 1×3-4µm and widely distributed in nature. B.cereus is commonly found in soil saprophytic organism.
R. rubrum is a facultative anearbic organism with size of 800 to 1000 nanometer. This organism is commonly used in alcoholic fermentation under low oxygen condition while M. luteus is a harmless bacterium that is commonly found in water, soil and human skin.They are 0.5-3.5 micrometer in diameter and they are gram +ve bacteria cocci.