Eight isolates of S. thermophilus did not form serotonin. Lb. hilgardii
X1B, isolated from wine, was able to degrade arginine by
two pathways: arginine deiminase and arginine decarboxylase.
Lb. hilgardii X1B converts arginine into agmatine by arginine decarboxylase
activity (Arena & Manca de Nadra, 2001). All S. thermophilus
isolates induce agmatine production. Apart from one isolate, all
strains produced small quantities of agmatine