What are strains in bacteria

Bacterial strainsResistant to antibiotics

"Staphylococcus aureus is usually yellow-gold, which is why it is also called Staphylococcus aureus because of its color."

Gudrun Koch holds a petri dish in her hand. Circular bacterial colonies grow on the yellowish nutrient medium in the plastic dish. The golden yellow spots in the middle are the wild type of the bacterium, around which a ring of mutated white daughter cells spreads.

"There are different mutants that don't express the genes and that's why they don't turn yellow, they have the white phenotype."

Bacteria mutate

Gudrun Koch and her colleagues at the Research Center for Infectious Diseases at the University of Würzburg are particularly interested in the mutants. They want to know how to fight Staphylococcus infections. That is why they look for the strains among the mutants that have altered properties, such as altered metabolism. In the colonies, the mutations occur again and again by themselves, because the close coexistence in such biofilms changes the cells, as Daniel Lopez explains.

"It's like a city of microbes. A small space in which millions and millions of bacteria coexist and interact. These interactions can be advantageous or disadvantageous for the individual pathogen, depending on the conditions and which strains are in the." City live together. "

Strains can become resistant

If the conditions are bad, there is competition for nutrients or oxygen. Then the bacteria have advantages, which can adapt to the conditions through mutations or push back the other types.

"A strain produces an antibiotic substance that exerts selective pressure on the others and gives it a growth advantage. The other bacteria react to this with mutations in order to evade the effect of the substance. Such a strain can then also be resistant to other antibiotics. "

Chain reaction in a mutation experiment

The Würzburg researchers also observed such a chain reaction in one of their mutation experiments. One of the white mutant strains appeared to have growth advantages over the orange wild type. After a while, colonies of light yellow bacteria also formed on the agar plate, which grew even better than the white ones. When the researchers took a closer look, they discovered that the white trunk released antibiotic substances that pushed back the orange. On the other hand, these substances could not harm the light yellow trunk, it had developed a resistance.

"They have to adapt. And the result is the emergence of a more robust tribe that is very difficult to control."

The light yellow trunk turned out to be such a case. The mutation not only protected him from the substance of the white competitor, but also from the antibiotic vancomycin, although the bacteria had never come into contact with it. Since vancomycin is actually used as a last resort when other antibiotics no longer work, such resistance is particularly problematic medically. For Daniel Lopez a reason to fight biofilms even more specifically.

"In bacterial colonies, competition can create spontaneous resistance to antibiotics. That is something we should take into account. We should adapt our antimicrobial strategies accordingly to prevent the colonies from even reaching the stages in which such interactions take place."

This is especially important in hospitals. Since staphylococci also settle on the skin, they can get inside the body when catheters or artificial joints are inserted, develop resistance there and cause infections that are difficult to treat. Daniel Lopez hopes that this can be prevented in the future.