The effect of amino-acids on the growth of Lactobacillus casei A.T.C. 7469 in pteroyl glutamic acid-free media

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Abstract
The titers of the blanks in media used for the microbiological estimation of pteroylglutamic acid (PGA) with L. casei depend on the amino acid content of the media and in particular on the amount of L-glutamic acid and DL-alpha-alanine present. Unrestricted growth of L. casei was obtained in PGA-free media containing certain combinations of L-glutamic acid and DL-alpha-alanine indicating that PGA could not be considered an essential growth factor for L. casei under those conditions. The amount of DL-alpha-alanine needed in media used for estimation of PGA must be determined by expt. for each medium with a different amino-acid content, such as may arise, for example, from the use of casein hydrolysates of different origins. The possibility of using PGA-free media of a defined amino-acid content for the assay of DL-alpha-alanine and L-glutamic acid is suggested.