How do antibiotics kill bacteria, but not us?

Clare Bryant answers...

Clare - Yeah, well that's the holy grail of any form of chemotherapy, which is a drug that will kill what you don't want but leave your healthy cells alone. So with bacteria it's relatively easy, because what you're aiming to do is to target something that's expressed by the bacteria, so some constituent of the bacterium that's not present in humans or animals. Bacteria for example... the classic example is penicillin. Bacteria have a very thick bacterial cell wall, which is made in a very unique way by a series of enzymes. And penicillin will actually target the enzymes that are in the bacterial cell walls. And those enzymes aren't present in humans or animals, so therefore you get a selective killing of the bacterium but you leave the mammalian cells alone.

Chris - Is that why we have a problem making good drugs for viruses? Because bacteria, being cells in their own right, are really different from our own tissue and cells; they're quite easy, relatively speaking, to find differences between them and us. Whereas viruses are part and parcel of us, when they infect us they're growing in our own cells, using all our own equipment; it's like they come in and hijack the premises, isn't it, and turn our factory into a virus factory instead. And therefore much harder to find a difference.

Clare - Yes, indeed. And this is the big issue with viruses, except that there are some unique viral target proteins, which is... then we use, for example, vaccination to generate an immune response, which will target a viral unique protein. It gets even more complicated with fungi, and then even further complicated with cancer, of course.