The determination of the most probable numbers of streptomycinfast cells in brucella cultures and their variability in growing and ageing cultures.

Su1MMARY: The method of most probable numbers (MI") was employed in order to determine the number of resistant brucella cells at concentrations of streptomycin of 1,lO and 100pg.lml. The examination showed agreement with the centrifugation method (plating of the sediment of at least 1OOml. of culture together with the required concentration of streptomycin) in a range up to 1000 resistant cells/100 ml. The method showed that there exist differences in the numbers of resistant cells in different strains, and that in cultures originating from the same colony variations occur. The general trend is a rtlative increase of the resistant cells with the age of the culture.