House for the right microbes

Look out the window at the house opposite. Surely its walls are covered with acne air conditioners. Without them, many do not represent a modern home, especially in the summer. So, if in the USA in 1965 air conditioners stood only in 10% of houses, then in our time they have already equipped 85% of residential and 95% of office buildings. The presence of a system of air conditioning in offices led to the fact that the frequency of respiratory diseases doubled compared to rooms with natural ventilation.

Respiratory diseases are the most common in the world. American children get them 6-8 times a year. About 300 million people around the world suffer from asthma, more than 40% of residents of developed countries - from allergies. Agents that cause these ailments are in the air of closed rooms, where people spend up to 90% of the time. At the same time, an adult pumps through the lungs of 16 thousand liters of air per day, the child - 3.5 thousand liters. Is it possible to make our houses so safe that the stay in them does not threaten a disease? This problem is devoted to the article by Professor of Yale University of Jordan Peccia and his graduate student Sarah E. Kwan [1].

Microbes are waiting for a person on the threshold of life: in the birth canal or on the skin of the mother, if the baby is born with a cesarean section. Although specialists of the medical college in Houston believe that the fateful meeting takes place much earlier. Researchers gathered in sterile conditions of 320 placenta samples and discovered the existence of a unique placental microbioma consisting of nonpathogenic representatives of FIRMICUTES, TENERICUTES, PrOTEOBACTERIA, BACTEROIDETES and FUUSOBACTERIA. In terms of species composition, this community is most reminiscent of the microbia of the oral cavity [2].

Then the child receives microbes from the skin of the mother, from her milk, from the air, from the surface of the crib and toys, from pets, etc. Then he goes to kindergarten and school and comes into contact with a large number of people who shake their microbes into the air and get them from there. Most of the bacteria in the room gets there mainly from people's skin, as well as through the ventilation system and from pets wool.

Professor Pecchia emphasizes that the conditions in modern houses are favorable for reducing microbial diversity. Air conditioners, for example, create a unique habitat, cool and wet, and moisture alternates with dryness. Not everyone will like such conditions, but those microorganisms that feel well in such an environment are settled throughout the room. They settle in dust, on the surface of the walls and ceiling, as a rule, their concentration in the house is more than on the street, especially if the building is poorly ventilated.

The point is not even that pathogenic and conditionally pathogenic bacteria found a shelter in dust and ventilation systems, although this often happens. The development of many diseases is facilitated by a small variety of human microbioma - a consequence of low bacterial diversity in urban premises. So, according to a large number of observations, asthma's disease is associated with environmental factors. Children who grow on farms are much less likely to suffer from this ailment than citizens. Representatives of Bacteroidetes and Firmicutes are protected from asthma, which are abundant in the intestines of rural residents.

Canadian scientists conducted a long study, during which they found that children who are likely to risk asthma, in the first three months of life, experience intestinal dysbiosis [3]. In this critical period, the infant intestines should be settled by representatives of three genera Firmicutes: Veillonella, Lachnospira and Faecalibacterium. At the age of age, children based on an allergic skin test and examination of the respiratory tract assessed the likelihood of sick asthma. At risk were children with a reduced number of Firmicutes. Apparently, products of metabolism of these bacteria, such as short-chain fatty acids, play an important role in protecting from asthma.

If these microorganisms are introduced into the intestines of wicked mice, their descendants, who have received the necessary bacteria at the beginning of life, are less likely to suffer from diseases that are transmitted by air. The microbial intestinal community of children from the risk group does not have such an effect on mice.

So, the microbes with which we are in contact in the room are not diverse enough, so people suffer from respiratory diseases. How to change the situation?

You can, for example, have a dog or cat. The presence of pets increases the species variety of bacteria and fungi in house dust and in the air. When living together, a person and his pets exchange microbes. In one study, mice in food mixed dust from houses where dogs live, and such an additive strengthened the immune protection of rodents from allergic diseases. Perhaps the maintenance of dogs in urban conditions can become an ersatz living on a farm.

Experts recommend monitoring humidity in the room. With high relative humidity (more than 75%) in dust, on the floor, objects of the situation, ceramic materials, gypsum and wood, mushrooms grow well. If the humidity is even higher, then the situation becomes favorable for bacteria. According to some studies, high humidity in the house weakens health, but this issue is still waiting for a detailed study.

Studies of home microflora have shown that microbes in the air of moderately filled rooms, such as school classes, mainly “cook in their own juice”: rise from the floor and walls, swirl, settled. Only a small part of them comes from the outside or leaves the room. It is very useful to ventilate the rooms well. There is an undoubted connection between the health and the intensity of ventilation [4].

The office ventilation with an intensity of 25 l/s per person allows you to reduce the prevalence of a “sick building” syndrome. This syndrome includes various ailments, which are exposed to inhabitants of the premises with artificial ventilation: infections transmitted by airborne droplets, allergies to domestic dust ticks and spores of mushrooms, irritation of the skin and mucous membranes, headache, fatigue and impaired attention.

With less intense ventilation, complaints about inflammation, respiratory infections and asthma symptoms begin, employees often take sick leave. According to another study, the risk of allergies in children in the northern climate can be reduced if more than half of the air volume changes in the room in the room. Builders and designers of buildings should provide active ventilation of the premises with external air, however, it should be borne in mind that the air can be contaminated on the outside than in the room.

To design and build a building in which microbes do not stagnate, you need to do a huge preliminary work. We will have to carefully work out the question of which factors affect the composition of microorganisms in the room: where do they come from, where they settled, how they circulate around the building, how they leave the room.

It is also necessary to conduct a full census of home microflora, evaluate the influence of each duskson on all the rest and the action of various microbial compositions on human health. This is a huge job. Having completed it, the researchers will take up the creation of a model of growth and decay of a microbial community, best adapted to a real situation.

Studies of home microflora have been going on for a long time, there is even a special scientific journal Indoor Air - “Air in the room”, which recently turned 20 years old. Apparently, many publications on this subject will appear in the coming years. But so far, experts are not able to design a house that will provide the composition of microflora safe for its inhabitants.