Spectrum and type of antibiotic action
Antibiotics – chemotherapeutic substances produced by microorganisms, animal cells, plants, as well as their derivatives and synthetic products, which have the selective ability to inhibit and retard the growth of microorganisms, as well as inhibit the development of malignant neoplasms.
For the period that has passed since the opening
According to the spectrum of action Antibiotics are divided into five groups depending on which microorganisms they affect. In addition, there are anticancer antibiotics, the producers of which are also actinomycetes. Each of these groups includes two subgroups: broad-spectrum and narrow-spectrum antibiotics.
Antibacterial antibiotics make up the most numerous group of drugs. It is dominated by broad-spectrum antibiotics, affecting the representatives of all three sections of bacteria. A broad spectrum antibiotics include aminoglycosides, tetracyclines, etc. Narrow-spectrum antibiotics are effective against a small circle of bacteria, for example, flight-myxines act on gracylucutine, vancomycin affects gram-positive bacteria.
In separate groups secrete anti-tuberculosis, anti-leprosy, antisyphilitic drugs.
Antifungal antibiotics include significantly fewer drugs. Amphotericin B, for example, is effective in treating candidosis, blastomycosis, and aspergillosis; At the same time, nystatin, acting on Candida fungi, is a narrow spectrum antibiotic.
Antiprotozoal and antiviral antibiotics There are a small number of drugs.
Antitumor antibiotics represented by drugs with a cytotoxic effect. Most of them are used in many types of tumors, for example, mitomycin C.
The effect of antibiotics on microorganisms is associated with their ability to inhibit certain biochemical reactions occurring in a microbial cell.
Depending on the mechanism of action, five groups of antibiotics are distinguished:
1. antibiotics that violate the synthesis of the cell wall. This group includes, for example, β-lactams. Preparations of this group are characterized by the highest selectivity of action: they kill bacteria and do not affect the cells of the microorganism, since the latter do not have the main component of the bacterial cell wall – peptidoglycan. In this regard, β-lactam antibiotics are the least toxic to the macroorganism;
2. antibiotics that violate the molecular organization and synthesis of cell membranes. Examples of such drugs are polymyxins, polyenes;
3. antibiotics that violate protein synthesis; This is the most numerous group of drugs. Representatives of this group are aminoglycosides, tetracyclines, macrolides, chloramphenicol, which cause a violation of protein synthesis at different levels;
4. antibiotics – inhibitors of the synthesis of nucleic acids. For example, quinolones disrupt DNA synthesis, rifampicin – RNA synthesis;
5. antibiotics that suppress the synthesis of purines and amino acids. This group includes, for example, sulfonamides.
The main producers of natural antibiotics are microorganisms, which, being in their natural environment (mainly in the soil), synthesize antibiotics as a means of survival in the struggle for existence. Animal and plant cells can also produce some substances with selective antimicrobial activity (for example, phytoncides), but they have not received widespread use in medicine as producers of antibiotics.
Thus, the main sources of obtaining natural and semi-synthetic antibiotics are:
• Actinomycetes (especially streptomycetes) – branching bacteria. They synthesize most natural antibiotics (80%).
• Mold fungi – synthesize natural beta-lactams (fungi of the genus Cephalosporium and Penicillium) H fusidic acid.
• Typical bacteria – for example, eubacteria, bacilli, pseudomonads – produce bacitracin, polymyxins and other substances with antibacterial action.
There are three main ways to get antibiotics:
• biological synthesis (this is how natural antibiotics are obtained – natural products of fermentation, when microbes are produced under optimal conditions that produce antibiotics in the course of their vital activity);
• biosynthesis followed chemical modifications (so create semi-synthetic antibiotics). First, a natural antibiotic is obtained by biosynthesis, and then its original molecule is modified by chemical modifications, for example, certain radicals are attached, as a result of which the antimicrobial and pharmacological characteristics of the preparation are improved;
• chemical synthesis (so get synthetic analogs natural antibiotics, such as chloramphenicol / levomycetin). These are substances that have the same structure.