Human faecal material. Coloured scanning electron micrograph (SEM) of human faeces. Among the organic matter are many bacteria (some coloured pink). At least 50 per cent of human faeces is made up of bacteria shed from the gut. Many of these bacteria are a normal part of the flora found in the intestines and are beneficial to digestion. However, some are pathogenic, such as Salmonella enterica and certain strains of Escherichia coli, and can cause foodborne illnesses.
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