What doesn't kill germs makes them stronger

Antibiotics accelerate the growth of bacteria

Kirill Stasevich, "Science and Life", based on materials Phys.org : Antibiotics can boost bacterial reproduction

We know that antibiotics work against bacteria, but it often happens that bacteria adapt to antibiotics. And then biologists and doctors have to look for new substances that would act on bacteria. Looking for such substances, it is extremely useful to know how drug resistance manifests itself in general, how it develops and what it depends on.

Researchers from the University of Exeter experimented with E. coli and the antibiotic doxycycline from a group of tetracyclines that inhibit protein biosynthesis in bacterial cells. E. coli after treatment with doxycycline, as expected, became resistant to the antibiotic, but, in addition, the bacteria began to grow faster, and as a result, their colonies turned out to be three times larger than the colonies of bacteria that had not tasted doxycycline. The ability to accelerate growth persisted even after the antibiotic was removed from the nutrient medium.

The adaptation of bacteria to an environment with an unfavorable factor is the most obvious example of how natural selection works: due to the fact that bacteria multiply with great rapidity, individuals (if one can say so about unicellular ones) with suitable mutations that allow them to survive in new conditions are soon fixed in their population.

And now the authors of the work have managed to find two zones in the genome of doxycycline-resistant E. coli in which major changes have occurred. Firstly, bacteria have acquired additional molecular pumps pumping the antibiotic out of the cell (however, this "know-how" has been observed many times before, and in different types of microorganisms).

Secondly, the pieces corresponding to the "sleeping" virus disappeared from the genome of E. coli. Many viruses can embed themselves in the DNA of the host, and so remain in it, passing from generation to generation and being in an inactive state. Viral genes can even be useful to a cell in some way - for example, E. coli with their help triggers the process of self–destruction. Why does she need it?

The fact is that when bacteria grow on a solid substrate, they form so–called biofilms in which bacterial cells are immersed in a special intercellular substance - the matrix. The biofilm holds very firmly on the surface of the substrate and is very resistant to physical and chemical influences. The biofilm matrix molecules are released from the collapsing cells, so that, by self-destructing, the bacteria help the colony grow.

But now E. coli were grown in a liquid medium, where it was simply impossible to form a biofilm. But by getting rid of the viral genes of self–destruction, the bacteria increased the "birth rate": after all, if the cell did not die, it will begin to divide and increase the number of the colony - which is especially timely when a dangerous antibiotic is floating around.

The full results of the research are published in Nature Ecology & Evolution (Reding-Roman et al., The unconstrained evolution of fast and efficient antibiotic-resistant bacterial genomes). Of course, bacteria have other ways to acquire drug resistance and increase their own numbers, despite therapy. However, in some cases (and especially in the case of pathogenic strains of E. coli), treatment can become more effective if we learn to take into account both molecular genetic tricks that have just been discussed.

Portal "Eternal youth" http://vechnayamolodost.ru  07.02.2017