Protective effect of reuterin-producing Lactobacillus reuteri against Listeria monocytogenes and Escherichia coli O157:H7 in semi-hard cheese

Bioprotective effect of reuterin-producing Lactobacillus reuteri INIA P572 was assessed in cheeses artificially contaminated with Listeria monocytogenes and Escherichia coli O157:H7 and ripened for 30 days. Reuterin production in cheese made with L. reuteri INIA P572 supplemented with 100 mM glycerol was confirmed up to 7 d of ripening with a maximum of 5.2 μmol/g at 1 day. L. reuteri was able to survive up to 5.37 log cfu/g in 30 d control cheese, although it was reduced to 2.59 log cfu/g when added simultaneously with glycerol. L. monocytogenes counts in control cheese were 4.31 log cfu/g after 30 days of ripening, whereas in cheese made with L. reuteri INIA P572 and 100 mM glycerol, this pathogen was only detectable by enrichment of 25 g samples from day 7 onwards. This antimicrobial strategy also diminished E. coli O157:H7 counts on day 1 by 5.53 log units with respect to control cheese. After 30 d, E. coli O157:H7 counts were 0.85 log cfu/g in control cheese, but the pathogen was not detected in 25 g cheese made with L. reuteri and 100 mM glycerol from day 7 onwards. Reuterin production in situ might be a feasible alternative to improve cheese safety that could also be exploited in the control of other undesirable microorganisms.