FISH-KILLING FACTOR PRODUCED BY PROTEUS VULGARIS

I. STUDIES ON THE PRODUCTION OF THE TOXIC FACTOR

Abstract

1. Killifish (Oryzias latipes) died when they were kept in water in which ground fish suspension had been added in various concentrations. Death was related to the growth of Proteus vulgaris in the water. 2. Killifish also died in water in which preparations of “peptone” or tryptic digest of casein had been dissolved. In this case also the growth of Proteus vul-garis was involved. 3. The bacteria themselves had no toxic action. Some toxic factor produced by the bacteria resulted in the death of fish. The production of the factor was not directly proportional to the degree of bacterial growth. 4. Various amino acids gave no support to toxic factor production. Some de-composition product of protein, probably some polypeptide, appeared to be changed into the toxic factor by the action of the bacteria. The toxic factor was produced sooner and to a greater degree as the peptone concentration was increased. 5. Toxic action of the factor was greater as the temperature increased. 7. Fish exposed to sub-lethal doses of Proteus vulgaris toxic factor and reex-posed after two days to a lethal concentration, died in the same manner as the fish which had never been exposed to the factor, showing that there is no possibility to produce in the fish any immunity to the factor. 7. The production of toxic factor affected by the shape of vessel in which the bacteria were incubated. Petri-dishes, which had far greater surface area than test tubes, were generally more suited for the production than test tubes.