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Journal of Dairy Science Vol. 44 No. 5 844-850
© 1961 by American Dairy Science Association ®
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Effect of Peptide-Rich Extracts on Acid Production by Oxytetracycline and Penicillin-Resistant Starters1

H. E. Kennedy2

Department of Dairy Technology, Ohio State University, Columbus

ABSTRACT

The effect of peptide-rich extracts, including pancreas extract, yeast extract, liver fraction L, tryptone, tryptose, neopeptone, casein hydrolysate, milk protein hydrolysate, and peptonized milk, on the acid production of oxytetracycline-sensitive and -resistant counterparts of Streptococcus lactis (10D) in skimmilk was determined. Additions of 0.5% of each stimulant enabled the resistant culture to produce acid in 8 hr., in concentrations equal to or in excess of that of the sensitive culture. The additives did not enable the sensitive culture to produce acid in the presence of the antibiotic.

The effect of pancreas extract on acid production by penicillin-sensitive and -resistant counterparts of five strains of S. lactis and two strains of Streptococcus cremoris was determined. Six of the seven penicillin-resistant cultures, supplemented with pancreas extract, produced acid in 8 hr. equal to or in excess of that developed by the parent strains. The pancreas extract did not enable the sensitive parent counterparts of these cultures to produce acid in the presence of low levels of penicillin. Likewise, the resistant cultures were unable to develop normal acid after supplementing with pancreas extract, if a level of penicillin was added in excess of the level tolerated by these cultures.

FOOTNOTES

1 Article No. 19: 60 of the Department of Dairy Technology, The Ohio State University. Supported by a grant from the U. S. Public Health Service (National Institutes of Health).

2 Present address: Johnson & Johnson, New Brunswick, N. J.






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Copyright © 1961 by the American Dairy Science Association ®.