Variability in Response of Lactic Streptococci to Stimulants in Extracts of Pancreas, Liver, and Yeast

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Abstract
This study was directed to ascertaining the cause of different growth responses by starter streptococci in milk and in milk supplemented with certain stimulatory extracts. Aqueous extracts of pancreas tissue, when added to milk, were stimulatory for the development of certain species of the family Lactobacteriaceae, but not for representative species of milk spoilage types of bacteria. Litmus milk agar bioautographs of paper chromatograms showed the presence of multiple stimulatory components in the pancreas extract. Preliminary tests indicated that these components were peptides. Extracts of liver and yeast also contained these same stimulatory factors. Various strains of Streptococcus lactis and mixed strain streptococci starter cultures differed in their response to the individual stimulatory components. All cultures responded to certain components while the response to others was irregular. There was evidence of an inverse relationship between the number of components to which a culture responded and the rate at which the culture grew in milk.