They found a bacterium visible to the human eye.他們發(fā)現(xiàn)了一種肉眼可見的細(xì)菌。They have isolated the bacterium in its pure form.他們已經(jīng)把細(xì)菌分離出來,使它們處于較純的狀態(tài).A bacterium is identified as the cause for his duodenal ulcer.一種細(xì)菌被斷定為造成他十二指腸潰瘍的根源....