EFFECT OF EXOGENOUS PROLINE, BETAINE, AND CARNITINE ON GROWTH OF LISTERIA-MONOCYTOGENES IN A MINIMAL MEDIUM

Three Listeria monocytogenes strains isolated from food or food-proces sing environments were used to assess the response of this species to salinity in a chemically defined minimal medium. Growth in a minimal m edium containing five essential amino acids and glucose as a carbon an d energy source was comparable to growth in a rich medium (brain heart infusion broth). In the absence and presence of 3% NaCl the final cel l numbers reached in minimal medium were 10(9) and 10(7) CFU/ml, respe ctively. Growth under the latter conditions could not be detected by s pectrophotometry by measuring A660. Apparently, this technique was not suitable for these experiments since the detection level was > 10(7) CFU/ml. Exogenously added proline (10 mM), trimethylglycine (betaine) (1 mM), and beta-hydroxy-gamma-N-trimethyl aminobutyrate (carnitine) ( 1 mM) significantly stimulated growth under osmotic stress conditions in minimal medium at both 37 and 10-degrees-C. Betaine and carnitine a re present in foods derived from plants and animals, respectively. The refore, these compounds can contribute significantly to growth of L. m onocytogenes in various foods at high osmolarities.