The introductory part
The idea of this science fiction work is based on modern studies of the intestinal microbiota. It has been found that bacteria in symbiosis with humans are able to influence their mental state. These facts were the prerequisites for my idea: perhaps in the future, with the help of gene modifications, bacterial strains will be created that, when placed in the human microbiome and at a certain level of functioning, will stabilize the levels of neurotransmitters, improve the nutrition of the nervous system and thus contribute to more efficient brain functioning as a whole. In addition, this type of intervention could theoretically be one of the varieties of long-term minimally invasive monotherapy of various mental disorders.

 
The main part

"We are doing everything to reduce the risks, but the technology is not yet as perfect as we would like to think."
This phrase is persistently spinning in my head.
I wanted to – and still want to – answer: "It's the twenty–second century!" - but I'm ashamed in front of a man, an honored doctor and professor, and it's inconvenient: I took them for the procedure and management, I would like to be grateful here, but only anger and guilt have been climbing out of her for the last couple of days.
And anxiety. Sure. 
Today, everyone knows that the higher the intelligence, the more productive the work of the brain, the higher the chance to close the circulation of nerve impulses to anything. And so much for anxiety, or even depression.
Today…
Anastasia strokes her son's hot forehead. He has a fever, but thank God he's asleep. He puffs and twitches a little in his sleep, and an oxygen cannula sticks out of his tiny nose, but since they can be together at least all day, then it's not that serious. Before, Matvey spent several days in a sterile box: this is how it is supposed to be after the procedure. If it gets really bad, he will be returned there.
Anastasia remembers her own procedure well, although it was a long time ago. It's okay – yes, because for adults, with an already formed microbiota, the risk is much higher that the new strain will simply be devoured by more tenacious neighbors. But in such a case, there are a couple of spare ones. As far as she knew–and was generally aware of the procedure–a special type of E. coli had been profoundly modified with plasmids about fifteen years ago. Modified in a special way, the bacteria settled in the intestine and began to produce in the human body a certain list of biologically active substances that reliably and permanently improve brain function.
For normal... no, let's just say, for average people, such a neighborhood usually gave greater endurance in relation to avalanche-like information flows, increased stress tolerance and reduced the risks of acute mental disorders. Benefits from all sides, both for the individual and for the state. The country needs healthy, productive citizens. It's not a sin to pay for this. Nevertheless, every year a certain category of citizens randomly entered the free program, as in a medical examination. One attempt is free of charge, due to the presence of local citizenship. If you are unlucky, you can pay for the next ones.
Nastya was lucky on the first try. Nothing seems to have changed... at first. But gradually the changes came. And soon it felt like it had always been that way. It's nice to immediately understand the meaning of most things. It's nice to remember everything that is important not to forget. It's nice... to be more stable and reliable even for yourself.
"Minus the patient for the psychiatrist," she usually jokingly summed up, sharing valuable experience with newcomers and doubters.
Jinxed it? That's what older relatives seemed to like to say. 
No, of course, although sometimes, in moments of weakness, it seemed even worse: she was to blame. After all, this is her son. So, he got everything–both advantages and disadvantages–from her.
So it seemed that greater clarity of mind only spoils the situation. When you understand everything that doctors say, it's hard to get rid of the idea that many factors are to blame for the dysfunction of the child's nervous system, but led by herself.
The child whimpers softly without waking up. She strokes his forehead again and reaches for water to drink and moisten the gauze to cover Matvey's forehead.
Planting a strain of bacteria is nonsense. For an adult. You drink a clearly measured portion, a test tube with "oat milk" (the main thing here is not to forget to hold your nose and quickly wash it down with water), and spend three days in an isolated box under constant supervision. Then – a battery of tests. Then – recommendations, discharge and life with a new, especially clear head. Even for healthy people, as it turned out, there is a lot to strive for.
It's more difficult with children. Babies are not carried out at all: there is no own microbiome yet, it is difficult to measure the dose, it is almost impossible to persuade to drink. In other ways, it has been poorly studied so far. And it's not a fact that a little person will need it: tests for intelligence, nervous stability and endurance are carried out only when a person begins to speak coherently. As a result, the verdict is: do you need help or are you so lucky with nature?
People like Matvey are another matter. "Difficult children." Almost untrained, overly moody, restless and nervous. Not every mistake of nature can be corrected, but mental retardation without severe brain damage has been learned to smooth out to the norm. The disadvantage of the procedure is only one: the immunity of a preschool child is still building relationships with the microcosm in the intestine, and third-party intervention at best does not lead to any result. But usually there is a reaction. It is more difficult than for adults. Most often, a couple of weeks in the hospital. The body will slowly clean up the extra guests, but outside it is almost always a fever. It could be worse: serotonin syndrome or other metabolic disorders, an overdose of "magic" substances that improve the functioning of the entire nervous system in the long term. There are only antibiotics here: urgently remove the dispersed guests, otherwise you can die. The attempt goes to waste. The first one, again, is paid for by the state.
You can opt out right away.
But failure is a guaranteed mental disability. But definitely alive. But once left without parents, it is not a fact that he will be able to fully exist. Of course, one always believes in the best, especially when the child has not even started school yet, but there are a lot of examples around. Especially when you perfectly understand what and where to look for.
"Hold on, Mommy, you're not the first, you're not the last."
It remains to hold on. You can stop at any time. The child is not able to decide. Consent to antibiotic therapy – and everything goes back to normal.
Or you keep sitting next to it, watching, catching moments of relief and waiting, waiting for the little body to get used to the new biome and the new metabolism. It's not gene therapy – it's much more interesting. Simpler and more complicated at the same time. Bacteria affect the host much more strongly than it seems at first glance. It is much easier to interfere in their "state" than to rewire every cell of an already born organism. Good science! But, of course, it is still not perfect. There is always something to strive for. However, those who have undergone the procedure can be considered a good help: someone will probably want to load their head with all its new power and help science in some way in the future, by the turn of the next decades and centuries.
And maybe Matvey, too, when he grows up…
Under the bubbling of Bobrov's apparatus, the tired Nastya dreams of an adult Matvey.
Maybe a scientist, or a pilot, or a famous musician…
A week later, Matvey, a professorially serious six–year-old peasant, is finally discharged home.