ABSTRACT
The genus Escherichia is composed of six gram-negative, rodshaped, and nonspore-forming bacterial species: Escherichia adecarboxylata, Escherichia blattae, Escherichia coli, Escherichia fergusonii, Escherichia hermanii, and Escherichia vulneris. Among these, E. coli is the most frequently isolated and the best understood and characterized living organism. E. coli cells measure about 2 µm in length and 0.5 µm in diameter. It is a facultative anaerobe, capable of reducing nitrates to nitrites and producing acid and gas when growing fermentatively on glucose or other carbohydrates. Most strains are oxidase-, citrate-, urease-, and hydrogen-sulŠde-negative. They are positive for indol production and the methyl red test and can be differentiated from the closely related Shigella and Salmonella by their ability to ferment lactose.1
