The viability of hemolytic streptococcus in certain solutions containing gelatin.

Abstract

For certain quantitative biologic tests it is necessary to use a suspending medium in which the streptococcus will survive without increase or diminution in numbers for a considerable length of time.

Falk has recently reviewed the extensive literature on the subject of the inhibitory effect of the cations of various salts on the biologic activities of bacteria and other cells. He concludes that balanced solutions containing two or more salts in the proper proportions preserve the life of bacteria better than either distilled water or solutions containing single salts unless they are very dilute.

Robertson, Sia and Woo have recently found that 0.1 to 0.125 per cent gelatin in distilled water or Locke's solution greatly increases the length of life of the pneumococcus in these fluids.

With these facts as a basis, experiments with a hemolytic streptococcus obtained from an acute gangrenous infection of the thigh have been carried out with six different fluids: 1, distilled water; 2, “normal” saline; 3, Locke's solution; 4, a balanced solution containing 1 per cent sodium chloride and 0.05 per cent calcium chloride (“20-1”); 5, 0.2 per cent sodium citrate; 6, a balanced solution containing 0.5 per cent sodium chloride, 0.5 per cent potassium chloride, 0.5 per cent calcium chloride and 0.1 per cent magnesium chloride (Zeug's mixture).

Each fluid was prepared both with and without 0.1 per cent gelatin and titrated after autoclaving to pH 7.8. The streptococcus was grown in 1 per cent dextrose digest broth, washed twice and then suspended in the solution to be tested at a standard concentration, approximately one billion organisms per cubic centimeter. per cubic centimeter. This was diluted down seven times with the fluid to be tested, each dilution containing a tenth of the number in the previous dilution so that the final dilution was estimated to contain 100 organisms.