STALING IN BACTERIAL CULTURES

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Abstract
"Staled" agar media containing a large number of viable bacterial cells does not permit visible surface growth of the homologous organism. The autoinhibitory effect of staled agar is no+ specific with strains of Escherichia coli, Aerobacter aerogenes, Bacillus cereus, and Micrococcus pyogenes var. aureus. The staling power of any strain and its sensitivity to staling by other strains are related, as are staling power and reducing ability. Potentiometric detns. of degree of reduction in staled media were made by applying Pt and calomel electrodes directly to the agar surface. The inhibition apparently is not caused by autoinhibitory substances in cultures or by "direct antagonism" by the viable cells present but is analogous to the cessation of growth in broth cultures. Supply of nutrients and O2 tension in relation to the reducing capacity of the organism seem to be implicated as controlling factors in this process.