The production of putrescine via the AGDI pathway has,
however, been described in L. brevis of non-dairy origin
by other authors [48, 56]. All the present strains of L. brevis
shown to be putrescine producers were also tyramine
producers. It has been suggested that, in this species, the
AGDI genetic determinants are linked to those of the TDC
pathway, producing a locus of acid resistance mechanisms
probably acquired by horizontal gene transfer [43,
48]. Two of the three L. curvatus strains tested produced
putrescine from agmatine and also returned positive PCR
results (Table 1); both strains were also able to produce
tyramine. As in L. brevis, BA-producing capacities of these
two strains have been related to acid resistance. The corresponding
genes have been described as lying adjacent to
one another in the chromosome of some dairy isolates of L.
curvatus [43].