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Superbugs and their evolution

  1. Oct 11, 2005 #1
    Why do antibiotic super bugs keep evolving more and more so they are resistant to antibiotics?

    Wouldn't this evolution be considered on a macroscale or would you say microscale seeing as how they are becoming stronger and stronger?

    It's interesting to learn that these things are becoming more and more powerful through last century and this century. Why do these things evolve so quickly and yet we as humans don't really have a greatly evolving immune system?

    Things like this make me wonder if it is somehow attached to a radiation source on earth we haven't discovered.. perhaps from the nukes in the 50s?
    Last edited: Oct 11, 2005
  2. jcsd
  3. Oct 11, 2005 #2


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    It is the evolution in its most basic sense : after the artificial selection through elimination of "weaker" species occurs (thanks to antibiotics), the surviving specimens interbreed thus creating the drug resistant offspring.

    Simply put if you kill the weak bugs, the strong bugs make strong babies with other strong bugs instead of weaker ones, and that the medication is simply ineffective against
  4. Oct 11, 2005 #3


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    The things is that antibiotics resistance genes have always been present in nature. By definition, antibiotics are naturally produce by microorganism, although most antibiotics nowadays are synthetics.

    So resistance gene can be swap between bacteria of the same or different species if those genes are carried on mobile genetic elements such as transposons and plasmids. Also some bacteria can pick up DNA from the environment and if there is enough homology the DNA will recombine in the chromosome. There is several example of these in publication.

    Also, mutation in the genes encoding the proteins targeted by antibiotics can accumulate. Several antibiotics have specific binding site and a change in one amino acid will significantly decrease the affinity of the antibiotics for that site. Again, several researchers study the mutation site on antibiotics target.

    So, you have genes that are naturally occuring and you got genetics variation, then you combine this with the misuse of antibiotics in medicine, lack of compliance from patient and the use of sublethal dose of antibiotics as growth promoter in farm animal. You end up with a great recipe and example of microevolution.

    these traits evolve quickly in bacteria because bacteria have a shorter generation time, some genes were already present in the environment and we did put a great pressure on the bacteria.
  5. Oct 12, 2005 #4


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    An important fact is that many of these resistant variants are from nature's side freaks, who are at an disadvantage under normal conditions compared to the non-resistant variant.

    Anti-biotics target some vital function of the bacterium; but if the bacterium has a flawed version of that vital function to begin with, it is by no means certain that our drug will be effective against that flawed version!

    Thus, by changing the bacterias' natural environment into an environment containing the drug, natural selection will pick out and favour an organism which is sub-optimal with respect to the drug-free environment.
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