Rapid Method for Demonstrating Bile Solubility of Diplococcus Pneumoniae.

A time-honored method for the differentation between Diplococcus pneurnoniae and Streptococcus, Viridans group), is the solubility of the former in bile or solutions of bile salts. A solution of sodium lauryl sulfate is often used, but is apparently less specific than that of sodium deoxycholate. We wished to simplify the accepted procedures, to avoid the necessity for subculture from the original "streak-plate," and to reduce the time required for positive identification of D. pneumoniae. The medium was conventional blood-agar in a petri dish. The fresh colony suspected of being D. pneumoniae was examined under a hand lens. On this colony was placed a loopful of 2% sodium deoxycholate (pH 7.0). The plate was incubated at 37 C for 30 min. On re-examination, the suspect colony, if D. pneumoniae, was found to have disappeared, leaving only the partially hemolyzed medium to help identify its previous location (Fig. 1). This technique has been used by us on 200 separate isolates of D. pneumoniae. The results have been confirmed by subculture to broth, followed by the usual solubility test with 2% sodium deoxycholate. There have been no falsenegative results. One hundred consecutive isolates of Streptococcus, Viridans group, 40 isolates of S. pyogenes, types A and D, and 25 isolates of Staphylococcus aureus, grown and tested under identical conditions, were insoluble. Twentv-five consecutive isolates of Haeniophilhs influenzae, Neisseriaceae, and Escherichia coli similarly resisted solution in the directly applied deoxycholate solution. The technique (lescribed pronmises a saving of time and medium in providing aceurate bacteriological identification of D. pneumoniae.