Utilization of Peptones and Peptone Fractions by Bacteria

An attempt was made to determine the minimum concentration of the different peptones which are necessary to support the growth of a group of aerobic microorganisms. The medium for this experiment was semi-solid glucose peptone agar, with the peptone being varied in amount and kind. The growth supporting properties of the peptones under investigation varied a great deal. The minimum concentration of peptone necessary for the growth of Shigella dysenteriae, Proteus vulgaris, Streptococcus lactis, and Salmonella pullorum was determined. Peptones appear to contain a substance which is toxic to Salmonella pullorum or else they lack a growth stimulating substance necessary for the propogation of this organism. The absence of nicotinic acid from the peptones does not seem to be the factor involved. Extraction of Bacto-peptone with several organic solvents did not affect its growth supporting properties. All the peptones tested contained enough compounds possessing the guanidine nucleus to give good tests for acetyl methyl carbinol when the latter was produced by bacteria. Several peptones were found which yielded superior tests for the demonstration of indol production. The production of hydrogen sulfide in the various peptones was compared employing three different media. All the peptones under investigation produced better results when bismuth sulfite was the indicator than when ferric citrate was employed. Advisor: Carl E. Georgi; George L. Peltier