• Question: Why can't you block the mutations of a bacterium permanently, so that the existing antibiotics still work? Why do bacteria and viruses mutate? What causes them to undergo this process?

    Asked by chickeny to Lyn, Katy, Paul, PB, Ruth on 21 Jun 2013.
    • Photo: Katy Brown

      Katy Brown answered on 21 Jun 2013:

      Mutations happen to every species. DNA needs to be copied to make new cells, but this process isn’t perfect and sometimes the DNA copies have mistakes. At the moment, we don’t know how to stop this in any animal – it still happens to humans, which causes some genetic diseases. Bacteria and viruses make lots and lots of copies of themselves, so the way their cells check for errors in the DNA is less accurate – if there are millions of copies of a bacterium it doesn’t matter if a few are mutated. Unfortunately, this also means they get lots of mutations which can help them avoid antibiotics and make them stronger.

      Even if we knew how to block mutations we can’t catch all the bacteria, treat them, then let them go again! Lots of the problems with bacterial disease are because bacteria are too small to see, they are everywhere and they grow really fast, so treating all the bacteria would be impossible.

    • Photo: Peter Balfe

      Peter Balfe answered on 21 Jun 2013:

      3 questions which I’ll answer 2,3,1

      Nothing is totally stable, so mutations will always happen. Some organisms, such as RNA viruses are much less stable than others and so mutate a lot. Causes are radiation, UV light, damaging chemical (mutagens), simple errors in their replication, etc. etc. The result is change.
      Nothing is permanent, but in the case of some viruses, notably HIV, we’ve developed methods to challenge the virus simultaneously with lots of drugs. This leads to a situation where no single mutation can give rise to “escape” from the whole panopoly of stuff we’re throwing at the virus . That is, the virus cannot become able to grow in the presence of the drug by any simple single mutation, it has to accumulate half a dozen mutations all together, inherently unlikely. We call this approach “combination therapy”. For HIV this can stop the virus and control it for years, if not decades.

      My prediction is that this will be the way we try to go with all therapies in the future, if we can develop the drugs needed.

    • Photo: Ee Lyn Lim

      Ee Lyn Lim answered on 22 Jun 2013:

      D’ye know, if we leave bacteria and viruses alone for ten, twenty years (still let them infect people but not try and kill them with any drugs), they would probably mutate so much that our currently existing antibiotics would work again! Mutations are random – in a pool of bacteria, some will mutate to be more able to resist antibiotics, whereas some will mutate to be even weaker. But we never see the weak ones because they’re killed off immediately, and only the strong ones are left – then all the offspring from these strong ones will also be strong, and eventually almost all the bacteria are able to resist that antibiotic. So when we use antibiotics and other drugs, we’re actually SELECTING for the bacteria and viruses which are resistant – getting rid of the weak ones so that the population as a whole becomes strong. We keep chasing them with stronger antibiotics, but we’re really pushing them ahead of us. That’s why it’s important not to misuse antibiotics!

      But I like Peter’s point about combination therapy – instead of pushing them from one direction, we come at them from all directions instead. We’ll get them yet!

    • Photo: Paul Waines

      Paul Waines answered on 25 Jun 2013:

      DNA- the ‘code for life’- is present in bacteria and viruses, as well as us. It is very clever stuff, but occasionally it will change very slightly when a cell divides, because it is not copied 100% accurately. The slight changes that result are called ‘mutations’, and these can sometimes give rise to traits which will help the bacteria or viruses to survive when, for example, they are treated with antibiotics. Because these mutations are quite random in nature, it is hard to block them permanently- as soon as you block one, another might pop up somewhere else!

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