Acute rheumatic fever and its etiology / by W.V. Shaw.

  • Shaw, W. Vernon (William Vernon)
Date:
[1903?]
Catalogue details

Licence: Public Domain Mark

Credit: Acute rheumatic fever and its etiology / by W.V. Shaw. Source: Wellcome Collection.

    7/22 (page 161)
    The micrococcus grows as a streptococcus, and though usually smaller than the Streptococcus pyogenes commonly met with, it might easily he mistaken for it. It grows well on the ordinary nutrient media, but I have found that it grows best on alkaline beef broth and glycerin blood agar. To grow the organism on blood agar, and yet avoid the injection of portions of fibrin along with the micrococci, I devised a special form of blood agar culture medium. The agar was melted, and allowed to cool to about 42' C. in sterile test-tubes. Into each tube a few drops of sterile blood (sometimes horse’s blood and sometimes rabbit’s blood) were introduced. The tubes were then sloped and allowed to set. They were subsequently incubated for thirty- six hours, and those that remained sterile set aside for use. I found that, with proper precautions, the blood agar was usually sterile in the majority of the tubes. The growth of the micrococcus on blood agar was characteristic in several features. After incubation for twenty-four hours at 37J C., small, discrete, colourless, and transparent colonies make their appearance at the site of inoculation. In another twenty-four hours these flatten out somewhat; and when the growth is very active, they may become continuous with one another, forming a film on the surface of the medium. Still further incubation, at 37 C., results in the colonies growing down into the medium. About the second day or earlier, i.e. thirty-six to forty-eight hours after inoculation, the blood agar undergoes a change in colour. The bright red colour is replaced by a dull brown or rusty appearance, or even a greenish- brown tint. This change is most marked when the growth of the micrococci is active and abundant, and it appears to take place more extensively in the rabbit’s blood agar than in the horse’s blood agar culture medium. The alteration is undoubtedly due to the micrococcus, as it does not occur in similar culture media incubated for the same length of time, but without previous inoculation. This colour change takes place only in that part of the medium where the organism is actually growing, and is closely analogous to that taking place in cultures of pneumococci growing on blood agar. In the case of several other varieties of micrococci investigated, this alteration in colour does not occur, e.g. with the Streptococcus pyogenes and the Streptococcus septiccemice. It is probably due to acid formation and reduction of the oxyhsemoglobin by the micrococci of rheumatism. As proving this point, the spectroscopic examination of the pigment is important. This shows the absence of oxyhaemoglobin in the brown pigment, and the presence of a body with the absorption bands of haemachromogen. This micrococcus grows on other solid media, e.g. on peptone agar 1 per cent, alkaline to phenolphthalein, on glycerin agar, and on peptone gelatin. The gelatin media are not liquefied. But on all these media the growth, in mv hands at least, soon ceases; and inoculations after ten days, from the initial cultivation, have frequently proved sterile. It will grow, however, in many of the fluid media. In milk, neutral to litmus, it grows fairly well, producing acid and clotting the caseinogen in about two days. In broth, neutral to litmus, it grows, but not rapidly, and with a tendency to die out. In peptone broth, 1 per cent, alkaline to phenolphthalein, it grows rapidly. But perhaps the most suitable fluid medium for the cultivation of this micrococcus is glycerin veal broth, con¬ taining 2 per cent, peptone and 1 per cent, alkaline to phenolphthalein. In this medium it grows rapidly, and does not die out for at least one month. W1 len growing in broth the micrococci form flocculi, and aggregations that tend to settle to the bottom of the containing vessel. The growth in veal broth is usually visible as a flocculent mass after twenty-four hours’ incubation. The growth then is extremely active. This is also shown by the 1 1-JL. OK PATH.—VOL. IX.