Antibiotics in microbiology: classification, methods of preparation and mechanism of action

Diseases haunt man all the time of his existence. Many would like to become invulnerable to various ailments, but, alas, these are only our desires so far. But steps are being taken to bring closer the moment when we will free ourselves from the yoke of disease. One of them belongs to microbiology - the creation of antibiotics. What are they? Which exist? What is their mechanism of action?

general information

Begin with terminology. Antibiotics are chemotherapeutic substances created by microorganisms, plants, animal cells, plus derivatives and synthetic products that have the selective ability to inhibit growth and inhibit various harmful miniature life forms and inhibit the development of malignant tumors.

Since their discovery, Erlich managed to get over ten thousand samples. So if someone is interested in the generally accepted classification of antibiotics in microbiology, then we are forced to upset you - it does not exist. Therefore, in this case, they often rely on various points, such as the chemical structure, spectrum of action, side effects, and so on. But you need to navigate with the help of something, right? And, as an option - the main recommendation division, which is based on the chemical structure of these substances.

So, in this case, the most popular are (fluorine) quinolones, nitrofurans, sulfonamides and imidazoles. If you know what caused the disease, then priority is given to the spectrum of action of antibiotics. Microbiology distinguishes five groups of drugs, depending on which microorganisms they affect most, antitumor drugs are allocated in a separate group. Additionally, each of them is divided into two subgroups. These are the so-called antibiotics of a narrow and wide spectrum of actions. In addition, separate subgroups of the intended purpose are distinguished. Why is it so hard? The thing is the lack of a unified system for the classification of drugs.

Problems when using

Alas, these substances, despite their attractive aspects, often have a number of disadvantages of varying degrees of danger. Speaking about global things, it is necessary to note first of all the resistance of bacteria to antibiotics. Microbiology is trying to solve this problem, but, alas, careless attitude of people to treatment, neglect of therapy until complete recovery, ignoring medical requirements for admission and a number of other factors do their dirty deed.

Antibiotic resistance is constantly growing. As a result, various negative consequences arise, such as superbacteria, which cannot be cured by existing medicines. And in such cases you have to rely only on the human body. It should be noted that increasing the resistance of harmful pathogens is a completely logical and expected result that would have occurred in any case. The only question is how fast this is happening.

The use of antibiotics in the form of small courses is widespread in the world, for prophylaxis, against viral diseases (from which they, as a rule, do not help at all, but this will be discussed in detail later) and a number of other cases, which together only contribute to the emergence of resistant strains. Some diseases have to be treated with several drugs at the same time, if during this process at least a slight break was allowed, then other drugs must be selected so as not to weaken the body's resistance.

In addition, one should not forget about sensitivity to antibiotics. Microbiology carefully studies this aspect of influence and tries to minimize the harmful effects on the human body. Conventionally, these drugs are divided into several groups, depending on the danger that they carry for people. The first is the most harmless, all the rest act more and more and cause more harm, because the side effects of antibiotics are growing. Microbiology, alas, cannot make them completely safe. Therefore, those that are most harmful (and often effective) are applied last.

Variety of objects of influence

The classification of antibiotics considered in microbiology, which is discussed below, is used to, in cases where it is known what has to be dealt with effectively and in a targeted manner, to act on pathogens. At the same time, it is one of the most popular:

1. Antibacterial antibiotics. They form the most numerous group of drugs. Broad-spectrum substances predominate in it, which affect all three departments of bacteria. These include tetracyclines, aminoglycosides and others. Narrow-spectrum antibiotics, as you might guess by their name, are effective only in relation to a small circle of bacteria. For example, polymyxins inhibit the development of gracilicut, and vancomycin gram-positive bacteria. Groups of anti-tuberculosis, anti-leprosy and anti-syphilitic drugs are distinguished here.
2. Antifungal antibiotics. There are already not many drugs. There are also broad and narrow spectrum antibiotics. As an example of the first, amphotericin B can be cited, which is effective for blastomycosis, aspergillosis, and candidiasis. A representative of the narrow spectrum is nystatin, which affects the fungi of the genus Candida.
3. Antiprotozoal antibiotics. These are medications that are used to suppress or destroy protozoa. They are not very many.
4. Antiviral antibiotics. There are a small number of drugs for this purpose. It should be noted that there is a popular misconception that antibiotics do not act on viruses. This is not true. It is more correct to say that the vast majority of antibiotics do not act on viruses. If you apply them against, say, SARS, then the result really will not be. After all, special preparations should be used.
5. Antitumor antibiotics. They are represented by drugs that have cytotoxic effects. Most of them can be used against a large number of tumors, for example, mitomycin C.

Classification based on mechanism of action

So, we know that these remedies can hit. And what is the mechanism of action of antibiotics? Microbiology has carefully studied this issue, and now we can confidently say that they are valuable due to the ability to suppress certain biochemical reactions that occur in a microbial cell. Let's take a closer look at this. In this case, five groups are also distinguished:

1. Substances that disrupt the synthesis of the cell wall. As an example, β-lactams. A feature of this group of drugs is that they have an extremely high selectivity of action. So, they kill bacteria exclusively, while the cells of the body are not interested in them. This is due to the fact that the latter in their composition do not have the main component of the bacterial wall - peptidoglycan. Therefore, antibiotics of this group are the least toxic.
2. Substances that disrupt the synthesis of cell membranes and molecular organization. Examples include polyenes and polymyxins.
3. Substances that disrupt protein synthesis. These are representatives of the largest group of drugs. The specificity of their action is to cause disturbances in protein synthesis at various levels. Among the representatives of this group, we should recall aminoglycosides, tetracyclines, macrolides, chloramphenicol.
4. Substances that are inhibitors of the synthesis of nucleic acids. As an example, quinolones that interfere with the formation of DNA can be distinguished. Or rifampicin - interfering with RNA synthesis.
5. Substances that inhibit the formation of purines and amino acids. Examples include sulfonamides.

And how are they created?

What are the ways to get antibiotics? Microbiology mainly relies on microorganisms that, while living in their natural environment (usually in the soil), synthesize antibiotics. They use them in the struggle for existence. Are they all antibiotic producers? Microbiology has established that plant and animal cells can also produce substances with selective antimicrobial activity. The most famous of them are volatile. But it should be noted that in medicine they have not received wide recognition as producers. So, natural and semi-synthetic antibiotics are obtained from such organisms:

1. Actinomycetes are branching bacteria. They account for the majority of created natural antibiotics (about 80%).
2. Mold mushrooms. We appreciate their ability to synthesize fusidic acid and natural beta-lactams.
3. Typical bacteria like bacilli and pseudomonas. They create polymyxins, bacitracin and a number of other substances that adversely affect microorganisms.

But you can’t just take and eat the producers, because this is fraught with side effects. It is only necessary to obtain the necessary substances. Three main methods are used for this:

1. Biological synthesis. This is how natural antibiotics are obtained. In fact, they are natural fermentation products. To obtain the necessary antibiotics under optimal conditions, microbial producers are cultivated that secrete everything necessary in the process of life.
2. Biosynthesis and subsequent chemical modification. This is how semi-synthetic antibiotics are created. First get a natural product. Then its original molecule is changed through chemical modifications. For example, certain radicals are attached, due to which the pharmacological and antimicrobial characteristics of the drug are improved.
3. Chemical synthesis. Used to obtain synthetic analogues of natural antibiotics. An example is chloramphenicol or chloramphenicol.

How do microbes get resistance?

Antibiotic resistance is a situation where harmful factors are not destroyed by drugs. Bacteria are considered resistant if they cannot be neutralized (conditionally) by a safe concentration of the drug in the human body. Resistance is acquired and natural. In the first case, a biological regularity is manifested, which is associated with adaptation to environmental conditions. Let it to varying degrees, but it is true for all microorganisms and antibiotics.

It should be noted that over time, everything from eukaryotic forms to viruses adapts to medications. This factor is especially important in connection with nosocomial infections. They very often have multiple resilience, in medical terminology called polyresistance. It should be remembered that this property always develops, the only question is at what speed.

Natural resistance lies in the fact that some microbes are no longer influenced by certain families of antibiotics. This may be the result of an absent target (mycoplasmas do not have a cell wall, therefore they are insensitive to drugs that act at this level) or bacterial impermeability (gram-negative microbes can filter large-molecular compounds). Therefore, to assess the effectiveness of the drugs used, methods are used to determine the sensitivity of bacteria to antibiotics. Microbiology has very good achievements here.

How do I know if a drug will affect malware?

There are two large groups:

1. Breeding methods. In this case, agar or liquid culture medium is used. This group of methods is based on the use of double serial dilutions of the antibiotic concentration, when they go from the maximum to the minimum. For example, 100 μg / ml, 50, 25, and so on, until the test drug is no longer effective. It is introduced in various concentrations into a liquid nutrient medium or agar. Then comes the turn of the bacterial suspension of a certain density. It is placed on an agar surface or in an antibiotic broth. After an overnight incubation at a temperature of 35-37 degrees Celsius, the result is summed up. If microorganisms developed (the broth became cloudy or additionally captured part of the agar), then this indicates that the applied concentration is not enough. As the antibiotic concentration increases, microorganisms slow down growth. The first smallest value at which an increase in their number is not recorded is considered a threshold. It is called the minimum inhibitory concentration. It is measured in mg / l or in μg / g. These are very simple methods that allow you to know the sensitivity. M. O. to antibiotics. In microbiology, these methods are widespread.
2. Diffusion methods. Antibiotic discs or E-tests are used. So, first, the first option. In this case, agar is placed in a Petri dish. A bacterial suspension of a certain density is applied to it. After that, disks are placed in it that contain a certain amount of antibiotic. Diffusion leads to the formation of zones of inhibition of the growth of microorganisms. They are located near the drives. Then it is necessary to ensure the incubation of the plates overnight in a thermostat, maintaining a temperature of 35-37 degrees Celsius. After that, the result is studied by measuring the diameter of the suppressed zone near the disk. A similar method is carried out and the E-test. The only difference is that instead of a disk, use a strip containing an antibiotic concentration gradient , starting from the maximum dose and ending with the minimum. In the place where the ellipsoidal zone of growth suppression intersects, the value of the minimum inhibitory concentration is found. The disadvantage of this approach is the high cost of the strip.

As you can see, the second group can significantly facilitate and speed up the process. But if you need a quick determination of the sensitivity of bacteria to antibiotics, microbiology offers a pretty good choice for every taste and means.

Bacteriophages

A small digression should be made here. Namely, about antibiotics and bacteriophages in microbiology. A significant drawback of the former is that they have side effects. Many scientists are interested in how to minimize them. Someone is trying to improve them, while others are looking for an alternative. And one of them is bacteriophages. Interestingly, they were considered as a priority in medicine of the early twentieth century. But after antibiotics were discovered, they did not even recede into the background, but into the background.

In fact, these are active and living viruses that infect bacteria. As you know, they can reproduce only with the help of a living cell. And phages use malicious microbes for this. Among their advantages, a low probability of developing resistance should be mentioned. And they are not an invented remedy. These microorganisms are considered the most ancient form of viruses. They are very widespread in the external environment, in which they actively destroy various bacteria. In addition, they work with a certain type, that is, they do not affect other microorganisms. For example, sour-milk bacteria that we need for the process of digesting food. And at the same time phages are very effective.

For example, 90% of staphylococcus strains have their own "hunters". And if you remember that the beneficial microflora is safe, unlike antibiotics, then this is generally a great option. Bacteriophages do not interact with other substances, they do not affect the processes occurring in the body, therefore, they can be prescribed to children, pregnant women, people with sick kidneys.

What are the nuances?

The mechanism of action of antibiotics in microbiology often leads to an allergic reaction, and very often to the occurrence of a severe form of the disease. The immune system does not react to viruses like that. Nevertheless, bacteriophages are only a conditional analogue for antibiotics. They are registered very rarely. This is due to a number of problems. For example, the narrow specialization of drugs. Another significant minus is the duration of the course. So, for antibiotics, one week is enough, and there are those that are taken for only three days. While treatment with bacteriophages requires a month, and the course itself is divided into several stages.

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The use of antibiotics in medicine and microbiology has achieved amazing results. But victory over harmful life forms is still a long way off. The greatest danger is the development of antibiotic resistance. To prevent this process is almost impossible. Therefore, it is necessary to use affordable drugs in such a way as not to contribute to the development and further spread of resistance. Indeed, antibiotic production by microbiology will soon not keep pace with the emergence of new strains. How to achieve this? For this, it is necessary to use medications exclusively for indications and not to use them for prophylactic purposes. After 10-15 days of therapy, you need to change the antibiotic, if possible using a drug with a narrow spectrum of action.

It will not be superfluous to limit their use in veterinary medicine and not to use it as a growth factor. By the way, the methods for determining the sensitivity to antibiotics in microbiology do not allow us to find out what side effects will be on the body, which is treated with their help. Moreover, the effect can be not only on a person, but also on microbes, as well as on the effect of other drugs. First of all, it is necessary to recall the toxic effect. It depends on the drug, the dose used, the route of administration, and the condition of the patient. Alas, the methods for determining sensitivity to antibiotics in microbiology cannot provide this. You can find out only by conducting clinical trials in humans.

Complications often occur when structures or processes close to those in the cells of a macroorganism act as targets. The toxic effect has the greatest effect on children, pregnant women and people who have impaired renal and hepatic function. How is it manifested? The result may be neurotoxic, nephrotoxic, general toxic effects, inhibition of hematopoiesis and a number of other body dysfunctions. In addition, dysbiosis and endotoxic shock should be mentioned. So there is no need to joke with them.