Phenotypic Traits and Immunomodulatory Properties of Leuconostoc carnosum Isolated From Meat Products

Twelve strains of Leuconostoc carnosum from meat products were investigated in
terms of biochemical, physiological, and functional properties. The spectrum of sugars
fermented by L. carnosum strains was limited to few mono- and disaccharides,
consistently with the natural habitats of the species, including meat and fermented
vegetables. The strains were able to grow from 4 to 37C with an optimum of
approximately 32.5C. The ability to grow at temperatures compatible with refrigeration
and in presence of up to 60 g/L NaCl explains the high loads of L. carnosum frequently
described in many meat-based products. Six strains produced exopolysaccharides,
causing a ropy phenotype of colonies, according to the potential involvement on
L. carnosum in the appearance of slime in packed meat products. On the other side,
the study provides evidence of a potential protective role of L. carnosum WC0321 and
L. carnosum WC0323 against Listeria monocytogenes, consistently with the presence
in these strains of the genes encoding leucocin B. Some meat-based products intended
to be consumed without cooking may harbor up to 108 CFU/g of L. carnosum;
therefore, we investigated the potential impact of this load on health. No strains survived
the treatment with simulated gastric juice. Three selected strains were challenged
for the capability to colonize a mouse model and their immunomodulatory properties
were investigated. The strains did not colonize the intestine of mice during 10 days
of daily dietary administration. Intriguingly, despite the loss of viability during the
gastrointestinal transit, the strains exhibited different immunomodulatory effect on the
maturation of dendritic cells in vivo, the extent of which correlated to the production of
exopolysaccharides. The ability to stimulate the mucosal associated immune system in
such probiotic-like manner, the general absence of antibiotic resistance genes, and the
lack of the biosynthetic pathways for biogenic amines should reassure on the safety of
this species, with potential for exploitation of selected starters.