The causative agent of diphtheria, better known in medicine as Corynebacterium diphtheriae, was discovered and then successfully isolated on nutrient media in pure culture 100 years ago. Then, after several years of active study, its role in the occurrence and pathological development of an infectious disease was established. This became possible only after obtaining a specific toxin that the bacterium produces. It causes the death of the experimental animal, in which pathological symptoms are formed, similar to those observed in patients with diphtheria.
The causative agent of diphtheria belongs to the genus of corynebacteria. But at the same time, it is assigned to a separate group of coryneform bacteria. These are slightly curved sticks in which extensions or sharpenings are observed at the ends. They also have an atypical division, they seem to break in two, and at the same time they acquire a characteristic arrangement in the form of the
Latin letter V. But in the smears under study, you can see isolated, separately located sticks. The causative agent of diphtheria is a relatively large bacterium, its length reaches 8 microns. They do not have flagella, they do not form protective capsules. Another important property of diphtheria bacillus is the ability to form very strong toxins.
All types of corynebacteria are facultative anaerobes. They feel good both in the presence of oxygen and without it. Resistant to drying, although they do not have spores. If you expose a
pure culture to heating at 60 degrees, then it will be destroyed within one hour. And in pathological materials, that is, if they have protein protection, the diphtheria pathogen is able to maintain its vital activity from 40 to 60 minutes. at a temperature of 90 degrees. As for low temperatures, then no fatal effect on these microorganisms is observed. At normal concentrations in disinfectants, bacteria quickly die.
The causative agent of diphtheria is also characterized by a large polymorphism. It manifests itself not only in changes in thickness parameters, but also in a change in the shape itself. Branches, threadlike, segmented, swollen and bulbous sticks are distinguished in smears. At the same time, on their ends, on both sides, after 12 hours from the beginning of the growth of the culture, thickenings can be seen, the bacterium takes the form of a dumbbell. In these thickenings, with a special color, the so-called Babesh-Ernst grains (accumulations of valyutin grains) are found.
The causative agents of diphtheria are saprophytes. They relate to those microorganisms that constantly need organic substances. That is why the used nutrient medium for growing this microbe in the laboratory must certainly include amino acids in its composition. It can be cystine, alanine, methionine, valine. Elective media for corynebacteria are those that contain serum, blood, or ascitic fluid. Based on this, Leffler's nutrient medium was first developed, followed by Tyndall and Klauberg.