Microorganisms cause diseases i animals. For example , in humans , bacteria causes  such as tuberculosis , cholera , typhoid , etc. In cattle , the food and mouth disease  is caused by a virus. Also several microbes cause diseases in plants. For example , the productivity of wheat , orange , apple , etc is reduced due to microbial diseases in plants. Certain microbes , on entering into body , produce toxic substances. This leads to food poisoning. Some organisms such as fungus spoil our food. For example , bread when left unused under moist conditions gets spoilt by fungus , producing a cotton-like growth on the bread.