It is well known that the reactions of the media play an important part on the bacterial growth. However, our knowledge of relationship between the thermal death rates and the reactions of the media is rather poor, only a few papers having been published on it.
B
IGELOW and E
STY(1) (1920) found that the thermal death time of the typical thermophilic bacteria comes earlier under acidic condition than under neutral condition. W
EISS(2) (1921), E
STY and M
EYER(3) (1922) reported that the addition of acids or salts shorten the thermal viability of spores of
Clostridiurn botudinum. M
YERS(4) (1928) pointed out that the thermal death point and the thermal death t ?? me of
Bact. coli are lower and shorter in alkalin condition than that in neutral condition. W
OLF and F
OSTER(5) (1921) also studied the effect of different hydrogen-ion concentrations on the thermal death rates of plant pathogens, and O
RR(5) (1918) studied the effect of varying hydrogen-ion concentrations upon the rate of death of the spores of
Bacillus pseudotetanicus suspended in solution containing HCl at different temperatures. C
OHEN(6) (1922) studied the effect of varying hydrogen-ion concentrations and different temperatures (0°C-30°C) on
Bact. coli and
Bact. typhosum, and found that the death times become shorter with the hydrogen-ion concentration.
I studied the relation of the thermal death point to the time and pH-value in
Escherichia coli and 5 putrefactive bacteria-
Kruthia zopfi, Pseudomonas ovulis, Achromobacter multistriatum Seratia sp.,
Micrococcus sp.
The bacteria cultivated for 48 hours at 28°C (for
Escherichia coli, 24 hours at 37°C) were taken in broth of 0.1c c., and put into 10c.c. of the sterilized buffer solutions (pH value= 10.14-2.27), and were shaken carefully. Then they were put into ampullae (capacity, ca. 0.1c.c., dia. ca. 3mm ), sealed, heated at a definite temperature, after a definite time were cooled in water. The ampullae were disinfected with alcohol, the ends of them were cut off, then their contents were pipetted into the agar media with sterilized capillary, and were poured into the petri dishes.
Besides, I have used the ampullae, unheated and stood 4 hours, as a control.
The results obtained are shown in the tables 1-6.
From the tables it is clear that the effect of hydrogen-ion concentration on the thermal death points depends on the kind of bacteria, that the thermal death points and the thermal death times depend on the hydrogen-ion concentration, that the thermal death times at high temperature are shorter than that at low temperature in the same hydrogen-ion concentration, that the thermal death times of the same temperature are the longest in about the neutral condition, that the thermal death points of the same heating times are the highest in about the neutral condition, and that the effect of hydrogen-ion concentration at high temperature are greater than that at low temperatnre.
抄録全体を表示