Abstract
From 87 stock-cultures of Streptococcus equi, colonies of 3 different forms were isolated by cultivating their 18-20 hour broth cultures on agar plate. We intend to designate these 3 types respectively G-(granular), F-(flat) and C-(compact) types.
The present paper deals with the comparison of the morphological, cultural and biological characters of these 3 types with each other. The results obtained from our experiments are summarized as follows:
(1) The relation between the age of subculture and the appearance of each colony-type have been traced and it became known that the recently isolated strains always generate only G-type and those subcultured over 2 years produce the C-type or F-type. Cultures stocked over 5 years tend to turn completely into F-type. So it is considered that the G-type is the original colony form of Str. equi and the C-and F-types represent its variant forms. (Table 1).
(2) On the agar plate, the colony of G-type is round, minute (its diameter under 1 mm.), bluish-white, translucent and that of the F-type has almost the same form, but the C colony is markedly different from the colony of the other 2 types, namely, from variously sized, opalescent daughter-colonies on its surface, thus showing a granular appearance (Fig. I), while the F-type forms a smooth, flat colony, its thickened periphery being ringlike (Fig. II). The C colony has coarse surface, elevated at the centre like a cone. (Fig. III.)
(3) All 3 types grow luxuriously on blood (horse) agar. The G-type forms a wet-looking, glistening, transparent film, taking an appearnce of water-glass, which flows down along the slant in its highest growth of 18-20 hours. The F-type shows a growth almost similar to that of G-type, though weaker. The C-type grows far more scantly, compared with the former 2 types, and forms a dry-looking, greyish-white, opaque film.
(4) In broth, the G-type renders first the medium turbid and later forms a membraneous film at the bottom of the tube. The F-type shows minute flakes floating in the clear medium, later settling in a snowflake-like sediment. The C-type forms a granular sediment, later leaving the medium clear.
(5) All 3 types are Gram-positive. The organisms of the G- and F- types show presence of capsule distinctly demonstrable by Benians' method, but the C-type forms no capsule.
(6) Growing on agar, all of the 3 types assume generally a diplococcal form. In froth (8 hour culture), the G-type usually forms short chains of 2 or 4 spheres and the F-type chains of 4 or 6, while the C-type produces long twisted chains tending to settle.
(7) In blood agar shake-culture, the 3 types form alike a marked hemolytic zone measuring nearly 4.0 mm. in diameter around the deep colony.
(8) The hemolysin production of each type in broth culture was traced every 2 hours after incubation. The 3 types began to produce hemolysin already 2 hours after cultivation and seemed to show the greatest production in some 4 hours, and the hemolytic titre of broth culture revealed the highest in 6 hours of cultivation. Then the production of hemolysin diminished and simultaneously its destruction began, accordingly the hemolytic titre turned to decrease. When the production ceased and the destruction was completed, the hemolytic action of broth culture pin-point sized (under 0.5 mm.), compact, greyish-white and opaque. Under microscope, the G colony reveals protuberances originating disappeared, that of the G-and F-types in 16 hours of cultivation and that of the C-type showed the lower production in 14 hours. (Table 3).
(9) The colony of the 3 types forms an hemolytic zone uniformly both on horse-blood and sheep-blood agars, whether they contain glucose or not. Thus, according to Kobayashi's classification, (10) the G-, F- and C-types all belong to the II type of Streptococcus.
