INTERACTIVE INHIBITORY ACTIVITIES AMONG CERTAIN PSYCHROTROPHIC BACTERIA FROM DAIRY FOODS1

Thirty-eight cultures, including species of Pseudomonas, Achromobacter and Alcaligenes, isolated at 5 C from refrigerated dairy foods were examined for interactive inhibitory activities by the spot-plate method. Eleven of the Pseudomonas cultures showed inhibitory activity against one of the Achromobacter species. Among the Pseudomonas species, eight showed inhibitory activity against four others. Neither the Achromobacter nor the Alcaligenes species were inhibitory against the other cultures. Inhibition was more pronounced at 7 than at 25 C and increased with increasing concentration of effector species and decreasing concentration of test species. When interacting species of Pseudomonas and Achromobacter were grown together in broth or skimmilk media, inhibition of the Achromobacter species occurred when the viable population level of the Pseudomonas species had reached 105–108 cells per ml. Sterile Seitz-filtered filtrates of Pseudomonas sp. 2 inhibited growth of Achromobacter sp. 54.