No abstract

The predominant spoilage fungi of dried and high-moisture prunes were members of the Aspergillus glaucus group and Xeromyces bisporus. Chrysosporium spp. were also important. At the mean pH of prune flesh (3.8) and at 25 C, X. bisporus grew at water activities (a,) down to 0.605, and Chrysosporium fastidium grew to 0.686. Germination was always followed by growth, but within the 120-day incubation period, the mninimum aw permitting asexual sporulation was usually higher than that permitting germination. Sexual sporulation often required an even higher aw. The water requirements of aspergilli were appreciably greater at this pH than near neutrality, no species germinating below 0.738 aw. This was probably a consequence of a high spore-death rate during incubation at low aw and pH.

The growth rates of Salmonella oranienburg have been determined in four different basal media in which the water activity (a,v) was controlled by addition of salts and by addition of sucrose. In three complex media the lower limit for growth was between 0�94 and 0�95 aw but in a simple defined medium the limiting aw for growth was between 0�96 and 0�97. When an amino acid mixture containing proline and methionine was added to salt-adjusted simple medium, growth occurred at 0�96 aw' Subsequent addition of eight watersoluble vitamins extended the growth range to 0�95 aw'

SUMMARYStaphylococcus aureus organisms, grown in basal medium of water activity (a,) 0.993 and in basal medium adjusted to several different a, values by addition of NaCl, were analysed for the following components: sodium, potassium, calcium, magnesium, total amino acids, inorganic phosphate, chloride, water, DNA, RNA, protein. Cell water decreased from 1-66 to 0.83 g./g. dry weight when a, was decreased from 0-993 to 0.90.Internal concentrations of solutes generally increased with decrease in h, potassium and phosphate concentrations being greatest at 0-92 a, and sodium, chloride, magnesium, and amino acids a t 0-90 a,, the lowest a, value studied. Increases in potassium and amino acid concentrations resulted largely from the decreased water contents of cocci grown at low a, values. Intracellular sodium and chloride concentrations were much lower than and proportional to the NaCl concentration in the medium. The predominant cell solute was potassium at 0-92 a, and above, and sodium below 0-92 a,. The data are discussed in relation to the inhibition of bacterial growth at low a, values.

The influence of water activity (aw ) on growth, respiration, and Na and K content of cells during respiration has been studied for Salmonella oranienburg. Sucrose, glucose, glycerol, NaCI, and KCI were added to control aw' The organism grew in a glucose-inorganic salts medium at 0�97 a", when any of these solutes was used to adjust a,v, but at 0�96 aw only when glycerol was employed. Respiration was not inhibited in glycerol-adjusted solutions at am's at which the rate was very low in other solutes. When a", was controlled by sucrose or glucose, cells oxidizing glucose accumulated K but not Na. Accumulation of K was greatest at 0�975 aw In solutions of NaCI, accumulation of K was small and in glycerol solutions it was absent. The differences between glycerol and the other solutes tested are discussed.