The isolation frequency of extended-spectrum beta-lactamase (ESBL) producing organisms, especially CTX-M-15 producing Escherichia coli, is increasing worldwide. The predominant ESBL producing E. coli epidemic clone in humans is O25b: H4-ST131. ESBL producers are isolated not only from infected patients but also healthy humans, domestic animals, foods and the environment. However few E.coli ST131 clone are isolated from domestic animals or foods. Futhermore CTX-M-1 or CTX-M-9 is the predominant subgroups found in human whereas the CTX-M-2 subgroup is the predominant ESBL isolated from non-human samples. Accordingly, there is no direct evidence of spread of ESBL producers between humans and domestic animals or foods.