• Question: How does bacteria become resistant to antibiotics?

    Asked by 534anta22 to Ceri, Marikka, Matt, Rob, Sally on 10 Nov 2014. This question was also asked by Illuminati_Overlord, marieescudie, andrealafuente, H1N1, Sarah LIMAME.
    • Photo: Sally Cutler

      Sally Cutler answered on 10 Nov 2014:

      Hi,
      Bacteria have a number of ways they can become resistant. They can respond to the selective pressure of antibiotics by mutating to produce variants that are no longer inhibited or killed by antibiotics. They can also acquire resistance genes from other microbes. These let them block entry of antibiotics into their cells, pump the antibiotic out quicker than it can get in, inactivate antibiotics or they can even bypass the antibiotic target. You have to admire the variety of mechanisms they can use to do this.

    • Photo: Robert Hampson

      Robert Hampson answered on 11 Nov 2014:

      In a single bacterial infection, there are millions of bacteria. Each of them has slightly different DNA. If you try and kill them all with antibiotics, some of them may be slightly resistant to it, so they are more likely to survive and reproduce. As this continues through many cycles, bacteria become more and more resistant.

      Some resistant bacteria pump the antibiotic out of their cell, some have small proteins which bind the antibiotic or digest it, some simply slightly change the target which the antibiotic is aiming at.

      There are two kinds of DNA in bacteria, their main chromosomal DNA and then extra circles of DNA called plasmids. Many of these resistance traits sit on plasmids and plasmids can be copied and passed on to nearby bacteria which spreads the resistance phenomena around quickly.

    • Photo: Ceri Dare

      Ceri Dare answered on 11 Nov 2014:

      When a person takes antibiotics, the least resistant bacteria die, so the most resistant bacteria quickly multiply to take their place. Any antibiotic is going to work better on some bacteria than others, so resistance is always going to evolve.

      Also, some bacteria have a clever trick where they can swap bits of DNA – like you deciding that you liked your friend’s ginger hair, so you were going to take a bit and grow it on your head! In this way, bacteria can pass resistance mechanisms to each other.

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