Probiotic Properties of Lactobacillus salivarius and Closely Related Lactobacillus Species

BA Neville; PW O'Toole

Disclosures

Future Microbiol. 2010;5(5):759-774. 

In This Article

Lactobacillus salivarius & Its Clade

When it was first described, the genus Lactobacillus encompassed just over 50 species,.[1] Currently, however, the genus Lactobacillus contains more than 100 species assigned to twelve Lactobacillus clades, and two Pediococcus clades,[2] whereby clades are defined as major clusters in the 16S rRNA gene phylogeny. Several phylogenetic analyses have acknowledged the cohesion of the Lactobacillus salivarius clade, termed as such due to the extensive characterization of the L. salivarius species.[2–5] Presently, this clade comprises 25 species that have been isolated from humans, animals, food and environmental sources (Figure 1) & (Table 1).

Figure 1.

Summary of the species in the Lactobacillus salivarius clade and the general sources from which they were first isolated. A total of 25 species had been identified in the clade as of February 2010.[204]

The species L. salivarius owes its name to the 'salivary' properties of the oral cavity from which it was first isolated.[6] The name thus acknowledges the intrinsic association of the species with the mammalian digestive tract. Of taxonomic interest is the fact that L. salivarius was originally assigned two subspecies, either salivarius or salinicus according to its ability to ferment either rhamnose or salicin respectively.[6] However, the use of these subspecies descriptors was recently discontinued on the basis of a polyphasic analysis, which included microbiological and molecular analyses of a bank of 32 L. salivarius strains.[7]

Lactobacillus salivarius has gained attention in recent years as a promising probiotic species.[8–11] Probiotics are defined as "…living micro-organisms which upon ingestion in certain numbers exert health benefits (on their host) beyond inherent nutrition".[12] Thus, probiotics and their probiotic action by definition must be considered in the context of a whole organism or living system. Of particular interest is the L. salivarius strain UCC118. This strain was isolated from the terminal ileum of a human in Cork, Ireland, and it was shown to exhibit several potentially probiotic traits[8,13] that have since been further characterized (Table 2). Research on L. salivarius UCC118 was greatly assisted by the sequencing, assembly and annotation of its 2.13-Mb genome, which revealed a multireplicon genome architecture.[14] In particular, the identification of a circular genomic megaplasmid was exceptionally novel amongst lactobacilli.[14] The contribution of the megaplasmid to the probiosis of L. salivarius has since been well studied, and megaplasmids have been identified in 33 L. salivarius strains and in at least six other Lactobacillus species.[15]

Although the number of species identified in the L. salivarius clade has increased rapidly in recent years, few other clade members have been thoroughly investigated, and these species are currently under-represented in the published literature. This article aims to discuss the potentially probiotic properties of the species found in the L. salivarius clade, with particular emphasis on the probiotic strain L. salivarius UCC118.

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