The spirillum of Asiatic cholera (Koch, 1884) generally appears, in the body and in artificial culture, broken into elements known as "commas." These are curved rods with round ends, showing an almost equal diameter throughout, and sometimes united in pairs or even a chain (spirillum). The latter rarely occur in the intestine, but may be seen in fluid cultures. The common site for Koch's comma is in the intestinal wall, crowding the lumina of the intestinal glands, situated between the epithelium and the basement membrane, abundant in the detached flakes of mucous membrane, and free in the contents of the intestine. They do not occur in the blood, nor are they distributed in the organs of the body.
The Comma-Shaped Bacilli of Cholera
The bacilli are actively motile, and possess at least one terminal flagellum. The organism is aërobic, and liquefies gelatine. It stains readily with the ordinary aniline dyes. It does not produce spores, though certain refractile bodies inside the protoplasm of the bacillus in old cultures have been regarded as such. The virulence of the bacillus is readily attenuated, and both the virulence and morphology appear to show in different localities and under different conditions of artificial cultivation a large variety of what are termed involution forms. Unless the organism is constantly being sub-cultured, it will die. Acid, even the .2 per cent. present in the gastric juice, readily kills it. Desiccation, 55° C. for ten minutes, and weak chemicals have the same effect. The bacilli, however, have comparatively high powers of resistance to cold. Unless examined by the microscope in a fresh and young stage, it is difficult to differentiate Koch's comma from many other curved bacilli.
| Bacillus Typhosus (Showing Flagella) × 1000 | Bacillus Typhosus (Widal Reaction) (Agglutination by serum from typhoid patient) × 400 |
| Bacillus Coli Communis (From agar culture, 48 hours growth) × 1000 By permission of the Scientific Press, Limited | Bacillus Mycoides (Spore formation. From agar culture) × 1000 |
Its cultivation characters are not always distinctive. Microscopically the young colonies in gelatine appear as cream-coloured, irregularly round, and granular. Liquefaction sets in on the second day, producing a somewhat marked "pitting" of the medium, which soon becomes reduced to fluid. In the depth of gelatine the growth is very characteristic. An abundant, white, thick growth exactly follows the track of the needle, here and there often showing a break in continuity. Liquefaction sets in on the second day, and produces a distinctive "bubble" at the surface. The liquefied gelatine does not fall from the sides of the tube, as in the Finkler-Prior comma of cholera nostras, but occurs inside the border where the gelatine joins the glass. In the course of a week or two all the gelatine may be reduced to fluid. On agar Koch's comma produces with rapidity a thick, greyish, irregular growth. On potato, especially if slightly alkaline, an abundant brownish layer is formed. Broth and peptone water are excellent media. In milk it rapidly multiplies, curdling the medium, with production of acid. Unlike Bacillus coli, it does not form gas, but, like B. coli, it produces large quantities of indol and a reduction of nitrates to nitrites. Hence the indol test may be applied by simply adding to the peptone culture several drops of strong sulphuric acid, when in the course of several hours, if not at once, there will be produced a pink colour, the "cholera red reaction." Although it readily loses virulence, and its resistance is little, the comma bacillus retains its vitality for considerable periods in moist cultures, upon moist linen, or in moist soil. In cholera stools kept at ordinary room temperature the cholera bacillus will soon be outgrown by the putrefactive bacteria. The same is true of sewage water.
The lower animals do not suffer from any disease at all similar to Asiatic cholera, and hence it is impossible to fulfil the postulate of Koch dealing with animal inoculation. In this respect it is like typhoid. It is, however, provisionally accepted that Koch's bacillus is the cause of the disease. The four or five other bacteria which have from time to time been put forward as the cause of cholera have comparatively little evidence in their support. It is less from these, and more from several spirilla occurring in natural waters, that difficulties of diagnosis arise.
Some hold that, however many comma bacilli be introduced into the alimentary canal, they will not produce the disease unless there is some injury or disease of the wall of the intestine. It need hardly be added that cholera acts, like other pathogenic bacteria, by the production of toxins. Brieger separated cadaverin and putrescin and other bodies from cholera cultures, and other workers have separated a tox-albumen.
Methods of Diagnosis of Cholera:
1. The nature of the evacuations and the appearance of the mucous membrane of the intestine afford striking evidence in favour of a positive diagnosis. Nevertheless it is upon a minute examination of the flakes and pieces of detached epithelium that reliance must be placed. In these flakes will be found in cholera abundance of bacilli having the size, shape, and distribution of the specific comma of cholera. The size and shape have been already touched upon. The distribution is frequently in parallel lines, giving an appearance which Koch described as the "fish-in-stream arrangement." This distribution of comma bacilli in the flakes of watery stools is, when present, so characteristic of Asiatic cholera that it alone is sufficient for a definite diagnosis. But unfortunately it is not always present, and then search for other characters must be made.