[On the contamination of the citric acid fermentation. I. The contamination by representatives of Enterobacteriaceae (author's transl)].

Among the most dangerous bacterial contaminations of the citric acid fermentation is the so-called brown contamination, which is called forth by non pathogenic representatives of Enterobacteriaceae like Escherichia coli, Aerobacter aerogenes, Enterobacter cloacae and Proteus vulgaris, while other bacteria do not produce the mentioned contamination. There is given a comprehensive characterization of the brown contamination. Enterobacteriaceae interrupt the growth of the mycelium of the mold Aspergillus niger and stop the production of citric acid, produce a characteristic repugnant smell and reduce nitrate to nitrite. In a case of weak contamination the phenomena of the brown contamination do not appear, but the yield of citric acid is rather low. The contamination may be transferred successfully within the first 24 hrs. of incubation. The effect of the bacteria is determined by their virulence and some other factors.