Antibiotics of the last reserve make bacteria harden

(ORDO NEWS) — Swiss scientists have determined the mechanism of action of polymyxins, drugs that are used against bacteria that are resistant to most antibiotics. It turned out that they destroy cells, causing the crystallization of their membranes.

The more actively antibiotics are used in the fight against pathogenic microbes, the more resistance to these drugs spreads among them.

The most striking example of this is multi-resistant Pseudomonas aeruginosa (MRSA), which is insensitive to the action of most existing antibiotics.

Treatment of such infections is extremely difficult. It is in such cases that antibiotics of last resort, such as colistin and other polymyxins, are used.

Polymyxins have been known for more than half a century, although due to their toxicity they are used only when other means have been exhausted.

It has been established that they disrupt the functioning of cell membranes, but the specific mechanism of their action was still unknown.

A team of European biologists led by Sebastian Hiller from the University of Basel managed to figure it out.

Antibiotics of the last reserve make bacteria harden 2
Cell membranes under a microscope: on the left – before treatment with colistin (polymyxin E), on the right – after

Scientists treated E. coli bacteria of different strains, including those with resistance to this antibiotic, with different amounts of polymyxins.

Cell membranes were examined under an atomic force microscope: as a result, the researchers found that even minimal concentrations of colistin dramatically change the structure of cell membranes.

In place of a smooth and elastic surface, crystalline structures appear, similar to honeycombs.

Crystallization causes thinning of the membrane and increases its area. The cell membrane becomes fragile, making them unviable. Such a transformation was not observed only in colicin-resistant strains.

The higher the antibiotic concentration, the more noticeable were the changes in the membrane.

Apparently, colistin directly binds to lipopolysaccharides, which form the basis of cell membranes, transferring them to a new, crystalline phase.

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