present in the culture or dairy product [43–45], conferring
the ability to produce histamine upon them.
Of the 137 strains tested, seven produced tyramine
from tyrosine in broth, and were positive for tdcA in PCR
tests (Table 1). All these strains belonged to L. brevis or
L. curvatus. Tyramine-producing strains of these species
have been isolated from cheeses by other authors [44, 46,
47]. In L. brevis, tyramine production has been described
as a strain-level trait—perhaps horizontally acquired [44,
48]. For L. curvatus, there are insufficient data to confirm
whether it is a species- or strain-dependent trait. The majority
of L. curvatus strains isolated from meat, however,
were reported to be tyramine producers [49–51]. All the
present tyramine producers, independent of their species,
were ‘strong tyramine producers’ (Table 2). L. curvatus
strains have been described as strong tyramine producers
by other authors [47], showing high conversion rates in
broth media supplemented with tyrosine. L. brevis has also
been described as a strong tyramine producer, although different
media and conditions were assayed and variation in
tyramine production capacity was observed [52].
None of the tested strains was able to produce
β-phenylethylamine under the present assay conditions. No
specific phenylalanine decarboxylases have been described,
but several authors have reported that certain tyrosine
decarboxylases can use phenylalanine as an alternative substrate,
converting it into β-phenylethylamine [53]. In the
present work, only the E. faecalis positive control was able
to produce β-phenylethylamine in medium supplemented
with tyrosine (data not shown).
Putrescine is produced from arginine via a decarboxylation
and a deimination reaction [11, 54]. However, the
present in the culture or dairy product [43–45], conferringthe ability to produce histamine upon them.Of the 137 strains tested, seven produced tyraminefrom tyrosine in broth, and were positive for tdcA in PCRtests (Table 1). All these strains belonged to L. brevis orL. curvatus. Tyramine-producing strains of these specieshave been isolated from cheeses by other authors [44, 46,47]. In L. brevis, tyramine production has been describedas a strain-level trait—perhaps horizontally acquired [44,48]. For L. curvatus, there are insufficient data to confirmwhether it is a species- or strain-dependent trait. The majorityof L. curvatus strains isolated from meat, however,were reported to be tyramine producers [49–51]. All thepresent tyramine producers, independent of their species,were ‘strong tyramine producers’ (Table 2). L. curvatusstrains have been described as strong tyramine producersby other authors [47], showing high conversion rates inbroth media supplemented with tyrosine. L. brevis has alsobeen described as a strong tyramine producer, although differentmedia and conditions were assayed and variation intyramine production capacity was observed [52].None of the tested strains was able to produceβ-phenylethylamine under the present assay conditions. Nospecific phenylalanine decarboxylases have been described,but several authors have reported that certain tyrosinedecarboxylases can use phenylalanine as an alternative substrate,converting it into β-phenylethylamine [53]. In thepresent work, only the E. faecalis positive control was ableto produce β-phenylethylamine in medium supplementedwith tyrosine (data not shown).Putrescine is produced from arginine via a decarboxylationand a deimination reaction [11, 54]. However, the
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