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Studies have shown that the bacteria strains Eschericha coli and Streptococcus faecalis survive 2 to 8 days longer at 4°C than at 20°C in the same lake water samples. An addition of glucose to lake water increased survival of these bacteria strains by 2 to 4 days. An addition of peptone was even more effective. Survival of E. coli increased by 5-15 days, and of Str. faecalis by 11-19 days. It was also found that E. coli showed longer survival than Str. faecalis in water samples with no organic additives and those containing glucose. In the case of water samples with peptone, survival of the two strains did not differ.
Survival in an annual cycle of Escherichia coli, Streptococcus faecalis, Salmonella typhimurium and Salmonella typhi dublin were examined in non-sterilized lake water, water sterilized by heating in an autoclave (121°C/10 min.), incubated without light at 4 and 20°C, respectively. All examined bacterial strains generally survived for shorter periods in non-sterilized lake water than in sterilized lake water, and shorter at 20°C than at 4°C. Survival curves of these bacteria in non-sterilized lake water were similar to a logarythmic curve, whereas in sterilized lake water they resembled a sigmoidal curve regardless of incubation temperature. The time necessary for 90% reduction of these bacteria ranged from 1 to 32 days. It was generally shorter in non-sterilized lake water and longer for sterilized water; and it was shorter for Streptococcus faecalis and longer for Escherichia coli, Salmonella typhimurium and Salmonella typhi dublin. All four examined bacteria were more quickly reduced in summer, and slower in spring, autumn and winter.
Str faecalis with respect to its thermal stability is used for evaluation of the pasteurization effectiveness in canned meat. In this work conventional doses of heating expressed as P (Tₒ=72°C, z= 10°C) required for sterilization of luncheon meat contaminated with Str. faecalis (10⁶ cfu) and containing various concentrations of NaCI (2, 3 and 3.5%) and starch (2, 4 and 6%) were determined. The relation was described as follows: y = 6.242 - 0.997 where r = -0.9549. The heat doses expressed as P = 5 min and P = 10 min assured pasteurization of canned meat at aw ≥ 0.985 and 0.955 to 0.972, respectively. Theoretical calculations indicate that pasteurization value P = 6.26 min assures sterilization of the examined tins.
Studies were carried out on the survival of six strains of bacteria: Pseudomonas fluorescens, Pseudomonas aeruginosa, Escherichia coli, Streptococcus faecalis, Bacillus subtilis and Bacillus cereus in fish feeds stored for 72 days in -11°C, 5°C and 20°C. On the last day of the study live cells of all bacterial strains were found in the feed stored in -11°C, of three strains in 5°C and two in 20°C. Two strains, Bacillus subtilis and Bacillus cereus survived throughout the whole storage period in all three temperatures.
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