SUMMARY— The inhibition of outgrowth of spores of Clostridium botulinum Type E by the addition of different concentrations of various solutes to a trypticase‐peptone‐sucrose‐yeast extract medium (TPSY) was studied at different incubation temperatures. Solutes added to TPSY medium were sodium chloride (NaCl), sodium formate (NaCOOH), potassium chloride (KCI), sucrose and glucose. Incubation was at 30, 21.1, 15.6, 10 and 7.2°C, and growth was confirmed by mouse toxin assay. The effect of the solutes on the equilibrium relative humidities (ERHI of the various media was measured using the graphical interpolation method and expressed as water activity (aw). The possibility of an osmotic effect was also investigated. The molar (M) concentrations and osmotic pressures of the different solutes were calculated and related to the approximate inhibitory concentrations of 5.0% NaCl (aw 0.975), 6.0% KCI (aw 0.974), 5.5% NeCOOH (aw 0.9711, 38.5% sucrose (aw 0.976) and 22.5%. glucose (aw 0.970). The inhibitory salt concentrations were approximately 0.80 M and produced osmotic pressures of about 36.0 atmospheres. The approximate osmotic pressure of the inhibitory 1.12 and 1.24 M sucrose and glucose solutions were 25.08 and 27.97 atmospheres respectively. Growth response decreased as the incubation temperature decreased as measured by delayed outgrowth times and in decreased amount of cellular material produced by the Type E strains tested. Copyright © 1969, Wiley Blackwell. All rights reserved
