Streptococci: Starve them to death!

Every year, millions of people die from Streptococcus pneumonia infections. The bacterium first settles into the lungs where it causes pneumonia.

From the lungs it can move into the bloodstream and cause blood poisoning, and it is one of the very few bacteria that can cross the barrier between blood and brain. If it reaches the brain, it can cause meningitis.

Like many other pathogenic bacteria, Streptococcus pneumonia has many strategies for survival and proliferation. In line with the increasing development of antibiotic resistance, there is also an urgent need for finding ways to tackle this bacterium from many different angles.

Starving and giving up

At SDU, molecular biologists Patrick Rosendahl Andreassen and Mikkel Girke Jørgensen from the Department of Biochemistry and Molecular Biology are studying the bacterium to find out how to knock it down.

In a new study, they describe how they have managed to cut off the bacteria from an important source of nutrients in the lungs, causing it to starve and give up.

- Streptococcus pneumonia needs nutrition. We try to understand how it gets hold of that nutrition and whether we can prevent it, Patrick Rosendahl Andreassen explains.

No more sugar

In the bloodstream, the bacterium has relatively easy access to nutrition, but in the lungs, there is only one source of nutrition. Therefore, the researchers are concentrating on cutting off the bacteria from the nutrition source in the lungs.

The nutrients in the lungs are carbohydrates, made up of sugar molecules sitting on the outside of our cells. The bacterium uses a sensory system to recognize these sugar molecules, which it then cuts off and ingests.

Mikkel Girke Jørgensen and Patrick Rosendahl Andreassen are working on deactivating the bacterial sensory system so that it can no longer sense the sugar.

- The hypothesis is that if it cannot sense the sugar, it will not activate the system that otherwise cuts the sugar molecules off the cell. The consequence is that the bacterium will starve and die, says Mikkel Girke Jørgensen.

Mutated bacteria in mouse experiment

In an experiment, the two researchers infected mice with a mutated version of streptococci that had their sensory system de-activated.

The experiment ran for 48 hours and when it ended, the mice were still alive.

However, it is not long enough for the scientists to say with certainty that the bacteria had become harmless.

- But they grew slower in the mice and thus became less dangerous. Whether the mutated bacteria without the sensory system are also harmless under more natural conditions, we do not know. It is, as I said, still a hypothesis. But it fits well with previous research from other groups, so it's a hypothesis worth working on, says Patrick Rosendahl Andreassen.

Develope new drugs

Knowing how the bacterium senses the sugar molecules vital to them can lead to the development of more effective drugs.

Patrick Rosendahl Andreassen and Mikkel Girke Jørgensen emphasize that this approach is only one of many to fight back streptococci. As previously mentioned, Streptococcus pneumonia has a wealth of strategies making it a very successful survivor.

Among others, it has not only one, but a minimum of 13 sensory systems - so many have been found by scientists so far. So far, only one of these systems has been described by science.

Secretes toxin

- We have contributed to the mapping of yet another sensory system, so now we know the details of two of them. The rest we still don't know much about, say the researchers.

However, it seems that the sugar sensing system is the bacterium's most important method of finding nutrition when it is in the lungs, the researchers believe.

But no one knows what other strategies this bacterium has. It is, for example, also capable of secreting a toxin that kills the host cells, causing them to burst, so that the cell gut can be eaten by the bacteria.

Photo: Jezper, Adobe Stock