It is a short bacillus, 1.2 to 2μ × 0.5 to 0.8μ, but varying considerably in size according to the stage of its growth and the genera of animal or culture medium in which it is grown. It has rounded ends and is usually in pairs connected by an invisible band. It stains promptly in all the aqueous aniline colors, but loses the stain in a solution of iodine (Gram’s). Prolonged exposure of artificial cultures produces an uniform stain, while a transient exposure, and especially of bacilli obtained from the tissues, stains them most deeply at the ends (polar) and periphery, while the centre remains somewhat clear. This is less marked than in the bacillus of swine plague, yet serves to show the relation between this microbe and the colon group.
It is ærobic (facultative anærobic), non-liquefying, and, in fluids, very actively motile, the movements lasting for months in preserved specimens (Smith). It grows luxuriantly in various culture media, and especially in alkaline ones, at the room temperature, and most actively at 85° to 100° F. It may grow as low as 60° to 70° F. and as high as 104°. (Swine plague bacillus grows at 55.4°).
On peptonized gelatine the surface colonies are usually round and flattened, those in its substance globular and smaller, and those at the bottom expanded next the glass and rising in the center into the gelatine like a knob. At 48 hours they appear as opaque whitish points and slowly increase to ½ to 2 mm. They may be brown by transmitted light, the depth of color increasing with age. On agar the colonies are grayish, shining and translucent and may reach the size of 4 to 6 mm. On potato (alkaline) a straw yellow film is formed, darkening with growth. In bouillon a turbidity appears in 24 hours, and in 1 or 2 weeks a precipitate and surface film.
The bacillus is usually larger in the gelatine and smaller in the bouillon than it is in the tissues. It seems to produce neither phenol nor indol.
Its behavior with sugars is significant. It ferments glucose producing acid and gas; does not ferment saccharose nor lactose, but turns the saccharose solution alkaline (no gas). In bouillon containing muscle glucose, it may without additional glucose form a little gas. The swine plague bacillus ferments saccharose producing acids but no gas: it ferments neither glucose nor lactose but turns the former acid.
Milk is neither coagulated nor soured by the hog cholera bacillus, but in 3 to 4 weeks it undergoes a change, becoming saponified.
Cultures have no special nor offensive odor. Some varieties in close tubes may cause a faint acid odor.
Oxygen is not essential to the success of a culture. The colonies form as promptly and as large in the depths of gelatine, or in a vacuum, as if in free air.
The following table will serve to show differences between the hog cholera bacilli, and related pathogenic microbes:
| Hog Cholera. | McFadyean’s. | Swine Plague. |
|---|---|---|
| B. Choleræ Suis | Swine Fever B. | B. Pestis Suis |
| 1.2 to 2μ × 5 to 0.8μ | 2 to 2μ × 0.6μ | 0.8 to 1.5μ × 0.6 to 0.8μ |
| Ends rounded | Ends rounded | Ends rounded |
| Involution forms | Involution forms | |
| Actively motile in liquids | Actively motile | Nonmotile |
| Flagella | No Flagella | |
| Stains throughout, lighter in center | Polar or uniform faint stain | From fresh organs polar stain, from old cultures uniform |
| Bleaches in Gram’s (I) Solu | Bleaches in Gram’s (I) Solu | Bleaches in Gram’s (I) Solu |
| Ærobic (Fac. Anærobic) | Ærobic | Ærobic, (Fac. Anærobic) |
| Vigorous growth in alkaline nutrient fluids | Slight growth in alkaline nutrient fluids | Weak growth in alkaline nutrient fluids |
| Active growth on potato yellowish, becoming darker | No growth on potato | On potato at 37° C. a slight, thin gray, waxy layer |
| On gelatine, small, round brownish colonies | On gelatine light bluish colonies shading off insensibly at edges | On gelatine feeble growth or none |
| Nonliquefying | Nonliquefying | Nonliquefying |
| On agar conical colonies, grayish, white, semi- translucent shining | On agar slight, transparent, almost invisible growth | On agar, grayish translucent, or brown, knobbed, waving edges |
| In milk grows freely, no acid, no clot: Saponifies in 3 or 4 weeks | Grows in milk, no clot | Grows in milk, no acid, no clot |
| Forms no indol in pancreatic bouillon | Forms no indol in pancreatic bouillon | |
| Ferments glucose, forming acid and gas | Does not ferment glucose, forms acid, no gas | |
| Lactose not fermented | Lactose not fermented | |
| Saccharose not fermented; alkalinity; no gas | Saccharose fermented, forms acid, no gas | |
| Thermal death point (moist) 58° C. in 15 minutes | Thermal death point 58° C. in 10 minutes | Thermal death point (moist) 58° C. in 7 minutes |
| Desiccated it dies according to bulk in 7 to 49 days | Dies quickly, if dried at body temperature | Dies in 3 days if dried |
| Dies in water in 3 to 4 months | Dies in water in 10 to 15 days | |
| Dies in soil in 2 to 3 months | Dies in soil in 4 to 6 days | |
| Pathogenic to swine, rabbits, guinea pigs, mice, pigeons | Pathogenic to swine and rabbits | Pathogenic to swine, hens, pigeons, pheasants, sparrows, mice, rabbits, cattle, deer, guineapigs, etc. |
| Guinea pigs immune | ||
| Swine Erysipelas. | B. Coli Commune. | Typhoid Fever. |
| B. of S. Erysipelas | B. Typhi Abdominalis | |
| 1 to 1.5µ × 0.1 to 0.2µ | 2 to 3µ × 0.4 to 0.6µ | 1 to 3µ × 0.6 to 0.8µ |
| Ends rounded | Ends rounded | Ends rounded |
| Involution forms | Involution forms | |
| Nonmotile in liquids | Nonmotile or very slightly so | Motile |
| No flagella | No flagella | Flagella |
| Stains readily and uniformly | Stains uniformly or polar | Stains uniformly (points clear) |
| Stains in Gram’s (1) Solu | Bleaches in Gram’s | |
| Anærobic (F. Ærobic) | Ærobic (F. Anærobic) | Ærobic (F. Anærobic) |
| Active growth in common nutrient liquids at 37° C. | Grows well in usual nutrient liquids, even if acid | Grows well in usual nutrient liquids |
| Usually no growth on potato; variable | Yellowish thick white growth on potato | Grows on potato; transparent glistening surface |
| In gelatine stab-culture delicate feathery branching growth | In gelatine amber colonies, becoming brown; may be bubbles of gas | On gelatine clear colonies with radiating and encircling lines |
| Nonliquefying | Nonliquefying | Nonliquefying |
| Grows in milk; acidifies, often coagulates it | Acidifies and clots milk in 8 to 10 days | Acidifies milk growing freely |
| Thermal death point (moist) 58° C. in 10 minutes | Thermal death point (moist) 60° C. in 10 minutes | Thermal death point (moist) 56° C. in 10 minutes |
| Loses virulence rapidly when dried | ||
| Dies in water in 18 to 20 days | ||
| Lives and even multiplies in rich soils, manure, etc. | Lives and grows in fæces | |
| Loses virulence slowly in light and air | ||
| Pathogenic to swine, pigeons, sparrows, rabbits, white and house mice, white rats | ||
| Guinea pigs, field mice and hens immune | ||
| Hog Cholera. | McFadyean’s. | Swine Plague. |
| Hen or pigeon has slough where inoculated, diarrhœa, ruffled plumage, somnolence | Hen or pigeon dies in 48 hours, after drowsiness, drooping wings, sunken head, ruffled plumage, liquid stools, soft black comb and wattles, prostration | |
| Rabbits getting 0.1cc. virulent culture subcutem die in 5 to 7 days with enlarged spleen and necrotic liver foci | Rabbits getting 0.5 to 1cc. culture subcutem had tumor like walnut but recovered | Rabbits getting 0.01cc. culture subcutem die in 16 to 20 hours, with inflamed serosæ and lung; Petechiæ |
| Weaker culture kills in 10 to 20 days with enlarged spleen, or recovery ensues | Weak cultures kill in 4 to 10 days, with inflamed serosæ and suppuration | |
| Guinea pigs die in 7 to 12 days | Not pathogenic to Guinea-pig | Guinea pigs die in 1 to 4 days |
| Swine inoculated subcutem have often local lesions and bacilli, also in lymph glands, only exceptionally fatal | Swine inoculated have local lesions only, only exceptionally fatal | |
| Ingestion of virulent cultures by fasting pig causes bowel lesions and death | Ingestion of 30cc. by pigs proved always fatal | Ingestion of virulent cultures by pigs is usually harmless |
| Intravenous inoculation in pig causes septicæmic lesions and death, or chronic diseases and typical bowel ulcers | Intravenous inoculation causes septicæmia and death in 1 or 2 days | |
| Intrapulmonary infection causes pleuro-pneumonia | ||
| Swine erysipelas kills inoculated pigeon in 3 to 8 days, and rabbit in 4 to 8 days. | ||