II. Comparison of Inulin Bile Titration and Virulence of Pneumococcus

Abstract

As it might be possible to determine the variation of the virulence of the pneumococcus by means of the extent and rapidity of fermentation of inulin and the effect of different dilutions of bile salts on this reaction, a series of observations were carried out.

Sodium taurocholate was the bile salt chosen and in certain instances other substances such as cholesterin, sodium citrate and sodium bicarbonate were also incorporated in the solution. Normal saline was used as a vehicle throughout. A 24 hour culture of the pneumococcus was washed down with normal saline and transplants made from this suspension in inulin were incubated for 24 hours. Pneumococcus I was used routinely and type III merely employed at times in comparison. In all instances cultures were obtained from our laboratory stock supply.

In the first trials, the inulin media used contained no peptone but it was soon found that in many instances where the virulence of the microorganism was impaired, redness but no coagulation would occur. When peptone was added it apparently afforded a nidus for the enzymatic action of the pneumococcus and caused coagulation in many of the instances wherein it had not occurred previously. One-fourth per cent peptone was used thereafter as it had been found that equally good coagulation was produced on the addition of a trace to 2% of this substance.

The time of fermentation at 37°C. was next determined and it was noted that redness began to occur within 6 hours and that coagulation was complete in 17 hours. When, however, the peptone was omitted both the rapidity and the intensity of the reactions were decreased.

Observations were made with relation to the effect of the number of pneumococci transplanted into the inulin.