The closely related species of the Lactobacillus casei group (L. casei, L. paracasei and L. rhamnosus) are extensively studied because of their applications in food fermentations and as probiotics. Our results, now published in mSystems, show that many strains in this group are incorrectly classified. Surprisingly many bacteria classified as L. casei are misclassified and should be relabeled as L. paracasei instead. We found that reclassifying them to their most closely related type strain improves the functional predictive power of their taxonomy.

In addition, our findings may spark increased interest in the L. casei species. We found that after reclassification, only 10 genomes remain classified as L. casei. Moreover, these strains show very interesting properties. First, they all appear to be catalase positive. This suggests that they have an increased oxidative stress resistance. Second, we isolated a L. casei strain, AMBR2, from the human upper respiratory tract and discovered that it harbors one or even two large, glycosylated putative surface adhesins. This might inspire further exploration of this strain as a potential probiotic organism.

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