Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Food Technology


The effects of temperature, initial pH and presence of sodium acid pyrophosphate, sodium chloride and potassium chloride on the growth and thermonuclease production by Staphylococcus aureus Z88 in brain heart infusion broth were examined. A quantitative assay was developed to measure thermonuclease activity. Growth of S. aureus was monitored by measuring absorbance of broth cultures at 660 nm and by aerobic plate counts at specific time intervals. Aerobic plate counts were also used to determine the number of cells/ml present when nuclease could first be detected. At low temperatures of incubation, growth and thermonuclease production were delayed. At an initial pH of 5.3, growth and thermonuclease production of the organism were delayed. At an initial value of 8.3, pH growth and thermonuclease production were delayed but the final numbers of organisms and levels of thermonuclease produced were not affected. As the level of sodium acid pyrophosphate was increased, the pH of the medium became more acid. NaCl delayed growth and thermonuclease production to a greater extent in the broth medium than did KCl. On some occasions, nuclease was detected when 10('5) cells/ml were present. In all environments however, nuclease was always detected when greater than 10('6) cells/ml were present.



Digital Repository @ Iowa State University,

Copyright Owner

Deland Jay Myers



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175 pages

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Microbiology Commons