ENTEROBACTERIACEAE

             The predominant aerobic bacterial flora of the large intestine of human beings and animals is composed of non-sporing, non-acid fast, Gram negative bacilli. Members of this group are included in a complex family, Enterobacteriaceae. Some are capsulated, some not, some are motile and some non-motile. They are oxidase negative and catalase positive and reduce nitrates to nitrites, aerobes and facultative anaerobes, grow readily on ordinary media, MacConkey agar and ferment glucose in peptone water with the production of either acid or acid and gas. The property of lactose fermentation is of great importance for the isolation and identification of enterobacteria from clinical specimens.