The Effect of Culture Environment on Results Obtained with the Dilution Method of Determining Bacterial Population

Abstract

When culture media con- taining 8-9% NaCl were used for subculturing from dilutions of a Staphylococcus aureus culture, the dilution method gave uncommon "codes." (A code signifies the number of tubes out of 10 that show growth in each dilution. The "common" codes are those which may be expected to appear with greatest frequency, when all viable cells grow.) Codes that were uncommon after the customary 48 hrs." incubation, became common codes on continued incubation, as more of the tubes showed growth. In many instances, 200 hrs. of incubation were required for the complete stabilization of codes. Experimenters using the dilution method were warned to be alert for the appearance of uncommon codes as an indication of unfavorable culture environment.