a type of very small organism that lives in air, earth, water, plants, and animals, often one that causes disease

an illness caused by bacteria in drinking water 饮用水中细菌引起的疾病

The bacterium Streptococcus pneumoniae causes about a third of some 3,000 annual meningitis cases. 在每年约3000起脑膜炎病例中，1/3左右是由一种叫“肺炎链球菌”的细菌引起的。