Antagonism (from the Greek. antagonizomai - fight, compete) - irreconcilable contradiction, in which the struggle between two opposites takes the most acute. In organic nature antagonism is expressed in the struggle for existence.
The term is used in biology, Parasitology (antagonism host and parasite, and others), physiology (a. Fiziol. functions, A. ions and others), pharmacology (antagonism of drugs and poisons) and other Sciences to identify the opposite of actions of the two organisms or two phenomena that lead to the suppression of one of them, their mutual destruction or weakening.
The antagonism of microbes is one of the manifestations of interactions between microorganisms in nature, namely, that when the joint development of individuals of one species inhibit the activity of individuals of another species.
Based on the study of microbial antagonism occurred bacteriotherapy and antibiotic therapy. Because the normal microflora of the animal organism is able to suppress the development of many pathogenic microbes, she became one of the protective factors of the microorganism. In some pathological conditions, such as when long introduction of broad-spectrum antibiotics or dysentery, may change the composition of the normal microflora - dysbacteriosis. Against this background, facilitated the development of conditionally pathogenic microbes which parasitized before or caught from outside. One of the methods of struggle with dysbacteriosis is the introduction of bacteria, characteristic of normal microflora, so they settled down and suppressed the development of pathogenic species. For the first time this principle has been proposed I. I. Mechnikov to combat putrefactive processes in the intestine, which he attached great importance to the aging process. Currently, the drug antagonistically active strains of E. coli coli-bacteria is used to fight dysbacteriosis with dysentery and other diseases of the gastrointestinal tract.
Antagonism germs can be identified at joint cultivation of two or more species of microbes in liquid or solid media. In experiments on liquid medium antagonistic activity is determined by the change in the number of viable cells and populations of competing species within a certain time of incubation. The number of colonies test-microbe attributable after a certain time 100 colonies of strain-antagonist, called antibiotic index. More simple and clear method of planting on the surface of the dense medium. Subject microbe sow in the centre of Petri dishes or into the groove on its diameter, surrounded by sowing the test microbes of different types (Fig. 1 and 2). This method is widely used in the research of new antibiotics. Antibiotic diffuses in the environment in suppressing of more or less extensive zone the growth of sensitive bacteria. This method allows to identify and focus of the antagonism, and the quantity produced of the drug.
A. microbes was first discovered in bacteria, and then plasnewydd mushrooms. But later it turned out that the most active producers of antibiotic substances are actinobacteria. Microbes that are not antagonists in normal conditions, can become them when growing hungry environment. This event open for the first time, I. Schiller, was named violent, or directed, A. Substances released at that microbes in the environment, the nature of close to antibiotics (see). Wide practical application of these substances have not received yet.

Fig. 1. The growth of sensitive and resistant strains of bacteria around the colony streptomicine aktinomiceta A. globisporus streptomycini: 1 - Bact. coli; 2 - Staph, aureus; 3 - You. subtilis - source sensitive to streptomycin culture; 4 - Bact. coli; 5 - Staph, aureus; 6 - You. subtilis - resistant variants, experimentally obtained from the above crops (N. A. Krasilnikov).
Fig. 2. The definition of antagonistic properties microbe in a dense environment. Vertically - microbe antagonist; horizontally - test-germs.