Isolation of Bacteriophage Resistant Lactic Culture Strains with Known Temperature Sensitivity
Seven strains of Streptococcus cremoris and Streptococcus lactis were tested for temperature sensitivity on a temperature gradient bar. A temperature of 37 C was the optimum for differentiating between temperature-sensitive and insensitive strains. Temperature-insensitive strains produced cell masse...
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| Format: | Others |
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DigitalCommons@USU
1979
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| Online Access: | https://digitalcommons.usu.edu/etd/5208 https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=6252&context=etd |
| Summary: | Seven strains of Streptococcus cremoris and Streptococcus lactis were tested for temperature sensitivity on a temperature gradient bar. A temperature of 37 C was the optimum for differentiating between temperature-sensitive and insensitive strains. Temperature-insensitive strains produced cell masses with absorbance values of 0.1 or higher and activity levels of 1.0 (expressed as a decrease in pH) or above at 37 C. Temperature-sensitive strains failed to produce these cell masses and activity levels, Strain selection and resistant- mutant isolation made it possible to identify ten strains of Streptococci sufficiently free of phage sensitivity for use in a cheese plant rotation program. These resistant mutants failed after being successfully used in mixed cultures for a short period of time, They became either slow acid producers or were again attacked by new bacteriophages. More work is needed to successfully isolate phage-resistant mutants suitable for cheese starters. |
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