THE CHIEF DISEASE ORGANISMS FOUND IN WATER
We will now consider several of the more important disease-producing bacteria found in water.
Bacillus Typhosus (Eberth-Gaffky). In 1880–81 Eberth announced the discovery of this bacillus in cases of clinical enteric fever. In 1884 it was first cultivated outside the body by Gaffky. Since then other organisms have been held responsible for the causation of enteric (or typhoid) fever. In 1885 the B. coli communis was recognised, and it has been a matter of great debate amongst bacteriologists as to how far these two organisms are the same species, and the typhoid germ merely a higher evolution of the B. coli. The differentiating signs between them will be referred to shortly. Bacteriologists generally regard the Eberth-Gaffky bacillus as the specific cause of the disease, though complete proof is still wanting.
Bacteria of Typhoid Fever
Microscopic Characters (in pure culture). Rods, 2–4 µ long, .5 µ broad, having round ends. Sometimes threads are observable, being 10 µ in length. In the field of the microscope the bacilli differ in length from each other, but are all the same thickness approximately. Round and oval cells constantly occur even in pure culture, and many of these shorter forms of typhoid are identical in morphology with some of the many forms of Bacillus coli. There are no spores. Motility is marked; indeed, in young culture it is the most active pathogenic germ we know. The small forms dart about with extreme rapidity; the longer forms move in a vermicular manner. Its powers of movement are due to some five to twenty flagella of varying length, some of them being much longer than the bacillus itself, though, owing to the swelling of the bacillus under flagellum-staining methods, it is difficult to gauge this exactly. The flagella are terminal and lateral, and are elastic and wavy. Their active contraction produces an evident current in the field of the microscope.
Cultures. This organism may be isolated from ulcerated Peyer's patches in the intestine, from the liver, the spleen, and the mesenteric glands. Owing to the mixture of bacteria found elsewhere, it is generally best to isolate it from the spleen. The whole spleen is removed, and a portion of its capsule seared with a hot iron to destroy superficial organisms. With a sterilised knife a small cut is made into the substance of the organ, and by means of a sterilised platinum wire a little of the pulp is removed and traced over the surface of agar. Agar reveals a growth in about twenty-four hours at 37° C., which is the favourite temperature. A greyish, moist, irregular growth appears, but it is invariably attached to the track of the inoculating needle. On gelatine the growth is much the same, but its irregular edge is, if anything, more apparent. There is no liquefaction and no gas formation. On plates of gelatine the colonies appear large and spreading, with jagged edges. The whole colony appears raised and almost limpet-shaped, with delicate lines passing over its surface. There is an appearance under a low power of transparent iridescence. The growth on potato is termed "invisible," and is of the nature of a potato-coloured pellicle, which looks moist, and may at a late stage become a light brown in colour, particularly if the potato is alkaline. Milk is a favourable medium, and is rendered slightly acid. No coagulation takes place. Broth is rendered turbid.
Micro-pathology. Typhoid fever is an infiltration and coagulation, necrosis, and ulceration of the Peyer's patches in the small intestine of man. The mesenteric glands show the same features, except that there is no ulceration. The spleen is enlarged, and contains the germs of the disease in almost a pure culture. The bacillus is present in the intestinal contents and excreta, particularly so when the Peyer's glands have commenced ulceration. In the blood of the general circulation the bacillus is not demonstrable, except in very rare instances. Typhoid fever is not, like anthrax, a blood disease.
COMPARATIVE FEATURES OF BACILLUS TYPHOSUS AND B. COLI
| B. TYPHOSUS | B. COLI |
| Morphology: Cylindrical bacillus 2.4 µ, unequal lengths; some filaments. | Shorter, thicker; filaments rare. |
| Flagella: Long, wavy, spiral, and very numerous; movement very active. | Shorter, stiffer, fewer; movement less active. |
| On Gelatine and Agar: Angular, irregular, raised colonies; slow growth; translucent; medium remains clear. | Even edge, homogeneous; much larger, quicker growth, and less translucent than B. typhosus; medium becomes turbid or coloured. |
| In Gelatine: In ordinary gelatine and in sugar gelatine no gas is produced. | Under the same circumstances abundant gas is produced. |
| Milk: Not curdled by the bacillus. | Milk is coagulated (within three days). |
| Indol: The production of indol in ordinary broth is nil. | Indol is present. |
| Potato: The "invisible growth," if potato is acid. | Thick, yellow growth. |
| Lactose: Fermentation very slight. | Fermentation marked. |
| 25 per cent. Gelatine at 37° C.: Strongly and uniformly turbid (Klein). | Gelatine remains limpid and clear, but possesses thick pellicle. |
| Elsner's Iodised Potato Gelatine: Slow growth; small, very transparent colonies. | Very fast growth; larger, brown, less transparent colonies. |
| Widal's Test: Bacilli become motionless and clumped together when suspended in a drop of blood serum from a typhoid patient. | Bacilli remain actively motile. |
| [59]Broth containing 0.3 per cent. Phenol or Formalin (1:7000): No growth. | Grows well. |
| Thermal Death Point: 62° C. for five minutes (Klein). | 66° C. for five minutes (Klein). |
| Vitality in Water and Sewage: Typhoid bacillus soon ceases to multiply and readily dies (Klein). | The B. coli retains for a much longer time its vitality and power of self-multiplication (Klein). |