We read with interest the article by Archambaud et al. (1) on Lactobacillus casei BL23 and Lactobacillus paracasei CNCM I-3689, which were able to limit the Listeria monocytogenes dissemination in a gnotobiotic humanized mouse model. The authors suggested that changes in the expression of IFN-stimulated genes and of mi-RNA, together with the L. monocytogenes metabolism redirection by Lactobacillus strains, may explain the modulation of the infection. However, according to the Occam’s razor principle postulating that a simpler explanation is more likely to be true, we believe that the role of bacteriocins is critical in this instance.
Bacteriocins have been used as bio-preservatives, especially against L. monocytogenes contamination in vegetable food matrices, for ∼20 y. The ability of Lactobacillus to inhibit pathogens in vitro is well documented. In one study, all of the L. casei and L. paracasei strains inhibited L. monocytogenes growth (2). The Lactocin 705 produced by L. casei CRL705 is bacteriostatic on L. monocytogenes (3), whereas a strain of L. paracasei subsp. paracasei has been shown to produce another substance inhibiting L. monocytogenes growth and leading to cellular lysis (4). Using the Bagel and Bactibase bacteriocin databases to analyze the strains used in this study, we were able to find one prebacteriocin (GenBank ID: YP_001988475) in L. casei BL23, and one Lactocin-705 (GenBank: LC70_LACPA) among available L. paracasei genomes.
Taken together, these data suggest that the impact of a Lactobacillus strain on the microbiota flora is mainly determined by its direct antibiotic activities, including bacteriocins, as recently rediscovered (5).
Footnotes
The authors declare no conflict of interest.
References
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