The causative agent of diphtheria, in medicine more commonly known as Corynebacterium diphtheriae, was discovered and then successfully isolated on nutrient media in pure culture even 100 years ago. At the same time, after several years of active study, his role in the emergence and pathological development of an infectious disease was established. This became possible only after obtaining a specific toxin, which is produced by the bacterium. It causes the death of the experimental animal, which develops pathological symptoms similar to those observed in patients with diphtheria.
The causative agent of diphtheria belongs to the genus of corynebacteria. However, he is classified as a separate group of coryneform bacteria. These are slightly curved sticks, in which extensions or tapering at the ends are observed. Also, they have an atypical division, they seem to break in two, while they acquire a characteristic arrangement in the form of the Latin letter V. But in the examined smears one can also see single, separately located sticks. The causative agent of diphtheria is a relatively large bacterium, its length reaches 8 μm. 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 kinds 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 a dispute. If you expose a clean culture to heating at 60 degrees, then it will break down within one hour. And in pathological materials, that is, if they have protein protection, the causative agent of diphtheria is able to maintain its vital functions from 40 to 60 minutes. At a temperature of 90 degrees. As for low temperatures, there is no harmful effect on these microorganisms. At the usual concentration 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 the thickness parameters, but also in the change in the shape itself. In smears distinguish branching, threadlike, segmented, swollen and bulbous sticks. At the same time, at their ends on both sides after 12 hours from the beginning of the culture growth, thickenings can be seen, the bacterium acquires a dumbbell shape. In these thickenings, with special coloring, the so-called Babesh-Ernst grains (accumulations of grains of currency) are found.
Diphtheria causative agents are saprophytes. They belong to those microorganisms that constantly need organic substances. That is why the nutrient medium used to grow this microbe in the laboratory must necessarily include amino acids. 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's media.