魚函の細菌汚染に関する研究-II

Abstract

In the previous paper1), the author reported on the invasion of the Takikawa's so-called pathogenic halophilic bacteria into the material of wooden fish container. It was also disclosed that the bacteria might easily migrate into inner part of such rough-grained wooden material as ceder or pine. In the present paper, studies have been undertaken to elucidate the fate of pathogenic halophilic bacteria being artificially polluted in the wooden test pieces for the period 60 to 90 days under various keeping conditions. The brief keeping conditions were as follows: Artificially polluted wooden pieces with the bacteria (pine and oak, 8×20×50mm; each piece has been dipped in the culture fluid of the test organisms at 30°C for 48 hours) were put in 6 large Petri dishes and each dish was let stand under following conditions. 1. Wet condition (moisture contents of the test pieces were higher than 57%). 1) Being kept in an refrigerator (0°C-5°C). 2) Being kept in a dark room during October to December at room temperature. 3) Being kept in an incubator at 30°C. For keeping wet condition, a small beaker filled with water was placed in each Petri dish, in addition, 2 to 3 drops of sterilized saline solution were added to each test piece every day. 3. Moderate condition The Petri dish has been kept in a dark room and allowed to stand at room temperature (with cover). The moisture contents of test pieces decreased gradually from the initial value 57% to 42%. 3. Dry condition Two dishes containing pieces of pine or oak respectively have been kept out door without cover and exposed to sunlight every day during October to December. Results obtained may be summarized as follows: Length of survival of the bacteria at the inner part of test piece varied according to the moisture contents. Apparently under wet condition, no appreciable decrease in bacterial number was observed, while the keeping temperature so far examined (0°C to 30°C) had a little effect on the rate of survival of the organisms (Figs. 1, 2 and 3). Under the dry condition, the bacteria on the surface of test pieces were diminished markedly within 15 days owing to the exposure to direct sunlight and loss of moisture in the piece (Figs. 5 and 6). From these experimental results, the author concludes that the most practical and effective method for treating a large number of wooden fish container at one time to diminish such harmful organisms as pathogenic halophilic bacteria would be the drying under sunshine for more than 10 days.