A Reported Growth Stimulant for Lactobacillus Casei

Pollack and Lindner (1) have reported the existence in natural extracts, particularly in Wilson's peptone, of a growth stimulant of unknown nature which is effective for Lactobacillus casei.In the course of following up this work it was found possible to improve the basal medium used, by the addition of a mixture of known compounds.When, for example, a modified basal medium containing 1.2 mg. of pyridoxine, 0.4 mg. of p-aminobenzoic acid, and 0.2 gm. of asparagine per liter was used, the addition of Wilson's peptone was found not to have a stimulating effect.The three additions mentioned were essential for a maximbm response; the addition of p-aminobenzoic acid alone had an inhibitory effect.The increased concentration of pyridexine was beneficial because "pseudopyridoxine" is the substance utilized by Lactobacillus casei (2), and it is not formed in optimal amounts unless the pyridoxine concentration in the medium is relatively high.The amount of asparagine used was relatively high and its effect when used alone was sufficiently small to justify the negative result reported by Pollack and Lindner.Subsequent to these preliminary experiments an attempt was made to prepare a mixture containing glutamine (which was found by Pollack and Lindner to be 5 to 10 times as potent as Wilson's peptone), p-aminobenzoic acid, and "pyridoxal" (3) which would, when added to Pollack and Lindner's basal medium in low concentrations, simulate or reproduce the effect of adding Wilson's peptone.The extent to which this was successful is indicated in Table I.The mixture contained 25.6 parts of glutamine to 0.001 part of p-aminobenzoic acid, and 0.02 part of pyridoxal, and the tests were carried out in accordance with the procedure of Pollack and Lindner except that the test media were steamed instead of autoclaved before inoculation.Separate tests not reported in detail showed that the mixture mentioned above was from 40 to 102 times as potent on a weight basis as Wilson's peptone.Since the growth-stimulating effect of the mixture is subs@-