Throughout its history, mankind has been fighting infectious diseases, and the discovery of antibiotics in the middle of the 20th century was a real breakthrough that radically affected the average life expectancy of people and the development of society.

Before the massive use of antibiotics in medicine, infectious diseases were one of the main causes of death, and for the same reason, infant mortality was very high. Before other diseases, which are the main causes of death now (cardiovascular problems and oncology), people simply did not have time to live, dying at a younger age from any infection. With the advent of antibiotics (and vaccines), the situation has changed dramatically, and many diseases have ceased to be fatal.

By now, we have accumulated a solid arsenal of highly effective means for fighting infections. They can be roughly divided into several main groups:

• antiseptics and disinfectants;
• antibiotics and synthetic antimicrobial agents;
• antiprotozoal agents;
• antiviral agents;
• antifungal agents;
• agents against mycobacteria;
• bacteriophages.

Let us dwell in more detail on the first two groups.

Are you still boiling?

The oldest means of disinfecting or sterilizing anything was fire. People burned tools, dishes and even cauterized wounds in the flame, which also made it possible to stop the bleeding. However, this method of destroying microbes was far from universal – not everything can be ignited in a flame. Therefore, it was replaced by antiseptics and disinfectants, they became the first chemical methods of fighting microbes. These are the simplest means that “kill everything”: both harmful (pathogenic microbes), and symbiotic (useful to us) microflora, and cells of our own organism – their action is completely non-selective.

Disinfectants are too aggressive, so they cannot be applied to the skin, mucous membranes, and even more so taken orally – this will lead to chemical burns and poisoning. They are used only for disinfecting surfaces, tools, dishes, and so on. Therefore, disinfectants are not drugs, despite the fact that they are actively used in medicine. Remember the familiar smell of bleach that meets us in almost any clinic.

Already medications, but not yet optimal

Antiseptics differ in that, although they do not act selectively, they are still not so aggressive, they can be applied to the skin and mucous membranes, and these are already drugs. The main disadvantage of antiseptics lies precisely in their high toxicity, which does not allow them to be taken orally or introduced into the blood. All antiseptics can only be used topically and / or topically.

One of the oldest antiseptics was and remains ethyl alcohol – the same “medical alcohol”. Moreover, the best antiseptic properties are not possessed by pure alcohol, as is often thought, but by a concentration of 70%. Stronger alcohol leads to very rapid denaturation (folding and compaction) of the surface proteins of bacterial cells, which slows down the flow of alcohol into the depths of the cell. Therefore, under this “armor” of their own denatured proteins, some bacteria can survive and continue to multiply when the alcohol evaporates. Alcohol of a lower concentration also does not have sufficient antiseptic properties, therefore, vodka or other strong alcohol, the concentration of alcohol in which rarely exceeds 40%, cannot be reliably disinfected.

Recently, antiseptics have been added to a huge number of household chemicals and cosmetics: antiseptic soap, toothpaste with antiseptics, even dishwashing detergent. They began to do this with a seemingly good purpose – to protect us from dangerous microbes, but life turned out to be more difficult. The very indiscriminate effect of antiseptics has become a problem. It turns out that beneficial bacteria live in our intestines, but also on the surface of the skin, as well as in the mouth. And, defending their habitat, they perfectly protect us from unwanted guests – dangerous pathogenic microbes.

Antiseptics, on the other hand, kill everyone, including beneficial microflora, which ultimately weakens the defense against dangerous bacteria.

Therefore, too frequent and widespread use of antiseptics leads to the opposite effect – the likelihood of infection increases. Of course, if you are going to dine in a public place, and you do not have the opportunity to wash your hands, an alcohol-based antiseptic liquid will be very useful. However, repeated daily use of, for example, triclosan soap will not do anything good (unless you work in the infectious diseases ward of a hospital).

In most cases, it is also not necessary to treat small wounds with antiseptics. It is enough to rinse the wound with clean water and seal it with a sterile plaster or apply a sterile bandage. The use of antiseptics in this case will only slow down the healing process.

Despite the fact that antiseptics and disinfectants are not selective, they also have their own spectrum of activity. For example, not all drugs can inactivate viral particles or bacterial spores. Therefore, when choosing a tool, you must definitely look at the spectrum of its activity. In addition, the antiseptic effect does not occur instantly. As a rule, it takes 1 to 10 – 15 minutes for the effect to develop. This information can also be found in the instructions and should be taken into account: if the preparation is washed off / dried too early, the required degree of disinfection may not be achieved.

Not all antibiotics are created equal

Antiseptics help solve many problems, but what if the microbes have already entered the body? Here you need a “magic bullet” that will allow you to kill a parasite (for example, a dangerous bacterium) without damaging the host’s body. This approach to the search for antimicrobial substances was formulated by Paul Ehrlich, who synthesized salvarsan at the beginning of the 20th century, the first effective remedy for the treatment of syphilis. This can be called the beginning of the era of antibiotics, although there were still about forty years before the discovery of penicillin.

But why then is salvarsan not an antibiotic? Here the question is in origin: the antibiotic must necessarily be a substance of natural (microbial) origin. Initially, with the help of antibiotics, some microbes fought with others; this is such a microbial chemical weapon. And the first antibiotics were completely natural. Then semi-synthetic drugs were obtained – when a natural antibiotic is subjected to chemical modification in order to improve its properties. In parallel with this, people synthesized a large number of compounds that also had antimicrobial activity and helped fight infections. These substances form another class – synthetic antimicrobial agents. Formally, they are not antibiotics, but very often in practice these classes are not distinguished, calling both antibiotics.

However, where does the “magic” come from in these “bullets”, and how does the antibiotic “understand” which cell needs to be killed and which one should not? This is where evolution comes in. Antibiotics most often interfere with the work of certain enzymes in bacterial cells – these enzymes can be responsible for the synthesis of proteins, the formation of a protective cell wall in bacteria, and so on. An antibiotic molecule binds to a molecule of one or another enzyme and disrupts its work, which leads to the termination of important processes in the bacterial cell, and it dies (this is how bactericidal antibiotics work) or stops multiplying (this is how bacteriostatic antibiotics work).

In the course of evolution, enzyme systems in humans (and other mammals) have undergone many changes and are now very different from bacterial ones: in some cases the spatial structure of the enzyme is different, in some cases we have no such enzymes at all. Therefore, antibiotics, which bind well to bacterial enzymes, affect the functioning of our cells to a much lesser extent. Of course, nothing is perfect, hence the side effects of antibiotics: they partially disrupt the work of our cells.

It turns out that antibiotics are more likely not “magic bullets”, but a very selective poison that can kill some organisms, affecting others to a much lesser extent. This principle – the search for “selective poisons” – is the basis of all chemotherapy: from antibiotics to the treatment of tumors. But the more the parasite’s organism resembles the host’s organism, the more difficult it is to select a remedy that would kill the parasite without harming the host. This is why most anticancer drugs have so many side effects: tumor cells are much more like our healthy cells than bacteria are.