Influence of a Film Yeast, Candida Krusei, on the Heat Resistance of Certain Lactic Acid Bacteria Grown in Symbiosis with it

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Abstract
After symbiosis with Candida krusei, Streptococcus thermophilus and Lactobacillus helveticus from near the surface film of milk cultures were more active following a severe heat treatment (62[degree] to 64[degree]C. for 30 min.) than bacteria from lower levels of the same culture. The influence of the film yeast was shown to extend for some distance below its active growing region. Filtrates of pure cultures of C. krusei contained substances which stimulated acid production by S. thermophilus. Mature bacterial cultures stored under conditions in which the apparent actions of the film yeast were stimulated by a reduction of acidity, a lowering of O2 tension, and the addition of Neopeptone, demonstrated that each of these treatments alone produced little effect on the heat resistance of the lactics, but that the combination of all 3 treatments markedly increased the heat resistance of S. thermophilus.