Inhibition of growth of a pathogenic strain of Staphylococcus aureus and production of a metabolite, thermostable deoxyribonuclease (TDNase), in acidophilus yogurt and yogurt were investigated. The causative factors of inhibition (lactic acid, hydrogen peroxide and bacteriocin) were assessed. Accumulation of hydrogen peroxide after 2 h of fermentation was 0.88 p-g/ml, which caused a significant difference in the population of S. aureus between yogurts with and without catalase. Growth of S. aureus in the acidified yogurt was reduced after 4 h of fermentation when the pH of the medium was 4.8 or lower. Significant differences were found for the S. aureus populations of the acidified treatment and acidophilus yogurt with catalase suggesting that inhibition was due to bacteriocin(s) produced during the yogurt fermentation. The TDNase was significantly lower in the acidified yogurt and was totally inhibited in the three cultured yogurts during the fermentation period.

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Author notes

1Published as Paper No. 8048, Journal Series, Agriculture Experiment Station, Lincoln, NE. Research was conducted under the Nebraska Agriculture Experiment Station Project 16-032, and supported by a grant from the Dairy Bureau of Canada.

2University of Nebraska.

3McGill University.