Biodiversity of Enterococcus faecalis based on genomic typing.

Enterococcus faecalis is a common inhabitant of the gastrointestinal tracts of different animals and is also found in other environments, such as plants, soil, food and water. The diverse nature of E. faecalis, which includes pathogenic, commensal and probiotic strains, calls for the development of tools for accurate discrimination and characterization at the strain level. Here we studied the genetic relationships among 106 E. faecalis strains isolated from diverse origins and possessing different degrees of virulence. Strain typing was conducted using a set of selected simple-sequence repeat (SSR) loci combined with multilocus sequence typing (MLST) analysis, which discriminated among the strains and separated them into three main clusters. While pathogenic and commensal isolates were dispersed along the dendrogram, probiotic and cheese-originated strains were highly associated with one specific cluster (cluster 1). The strain panel was further characterized by testing the occurrence of two virulence determinants (esp gene and ß-hemolysis). The two determinants showed low abundance among probiotic and cheese-originated strains within cluster 1 when compared to non-cluster 1 cheese-originated strains, indicating a possible association of cluster 1 with non-virulent strains. Our results further emphasize the importance and challenge of precise characterization of E. faecalis strains from various sources.

Indication for Co-evolution of Lactobacillus johnsonii with its hosts.

BACKGROUND: The intestinal microbiota, composed of complex bacterial populations, is host-specific and affected by environmental factors as well as host genetics. One important bacterial group is the lactic acid bacteria (LAB), which include many health-promoting strains. Here, we studied the genetic variation within a potentially probiotic LAB species, Lactobacillus johnsonii, isolated from various hosts. RESULTS: A wide survey of 104 fecal samples was carried out for the isolation of L. johnsonii. As part of the isolation procedure, terminal restriction fragment length polymorphism (tRFLP) was performed to identify L. johnsonii within a selected narrow spectrum of fecal LAB. The tRFLP results showed host specificity of two bacterial species, the Enterococcus faecium species cluster and Lactobacillus intestinalis, to different host taxonomic groups while the appearance of L. johnsonii and E. faecalis was not correlated with any taxonomic group. The survey ultimately resulted in the isolation of L. johnsonii from few host species. The genetic variation among the 47 L. johnsonii strains isolated from the various hosts was analyzed based on variation at simple sequence repeats (SSR) loci and multi-locus sequence typing (MLST) of conserved hypothetical genes. The genetic relationships among the strains inferred by each of the methods were similar, revealing three different clusters of L. johnsonii strains, each cluster consisting of strains from a different host, i.e. chickens, humans or mice. CONCLUSIONS: Our typing results support phylogenetic separation of L. johnsonii strains isolated from different animal hosts, suggesting specificity of L. johnsonii strains to their hosts. Taken together with the tRFLP results, that indicated the association of specific LAB species with the host taxonomy, our study supports co-evolution of the host and its intestinal lactic acid bacteria.