The cells found a dense protein coating resembling armor. It does not allow the antibiotic to penetrate inside.

The authors of the new work from the University of Newcastle have studied the “cellular armor” that protects bacteria from the penetration of even small molecules, in particular antibiotics. It is noted that the same S-layer can save clostridia from the action of protein enzymes, with which the affected cells themselves try to attack them.

Clostridia are spore-forming, Gram-positive, anaerobic bacilli that are widely distributed in dust, soil, and vegetation, and are normal flora in the gastrointestinal tract of mammals.

The authors examined the features of the functioning of the bacterium using the example of Clostridioides difficile, common representatives of the intestinal microflora. If degradation of the local microbiota occurs, for example, with the active use of antibiotics, then rectal colitis may begin. For its treatment, new antibiotics are needed, since the bacterium has a partial tolerance to them.

Other bacteria have similar armor, but the S-layer is especially dense in Clostridium. The gap between them reaches ten angstroms in diameter. For comparison, other bacteria have from 30 to 100 angstroms. Only a small number of molecules can squeeze through these holes.

The authors studied the protective functions of the S-layer – they created cells with partially removed details. Such organisms were more easily attacked by the body’s usual defenses, such as the enzyme lysozyme, which is found in salivary and lacrimal fluid.