Enterococcus solitarius

Abstract: During a previous study of the opsonic requirements for neutrophil (polymorphonuclear leukocyte [PMN])-mediated killing of enterococci, we identified two strains of Enterococcus faecium (TX0015 and TX0016) that were resistant to PMN-mediated killing. To better define the mechanism of this resistance, we examined phagocytosis with a fluorescence assay and found that TX0016 was completely resistant to phagocytosis by PMNs; this finding was confirmed by electron microscopy. Examination of multiple strains of enterococci revealed that all 20 strains of Enterococcus faecalis tested were readily phagocytosed (mean, 18 intracellular organisms per PMN; range, 7 to 28). In contrast, only 13 (50%) of 26 strains of E. faecium tested were susceptible to phagocytosis (> or = 7 organisms per PMN); the other 13 strains showed < or = 3 organisms per PMN. Enterococcus casseliflavus ATCC 25788 and one strain of Enterococcus hirae were also resistant to phagocytosis, while two strains of Enterococcus durans, Enterococcus mundtii ATCC 43186, and one strain each of Enterococcus raffinosus and Enterococcus solitarius were readily phagocytosed. Exposure of E. faecium TX0016 to sodium periodate, but not to the protease trypsin or pronase or to phospholipase C, eliminated resistance to phagocytosis. Sialic acid, a common periodate-sensitive structure used by microorganisms to resist opsonization, could not be demonstrated in E. faecium TX0016 by the thiobarbituric acid method, nor was phagocytosis of TX0016 altered by neuraminidase treatment. This study suggests that there is a difference in susceptibility to phagocytosis by PMNs between different species of enterococci and that a carbohydrate-containing moiety which is not sialic acid may be involved in the resistance of E. faecium TX0016 to phagocytosis.

Abstract: Deoxyribonucleic acid base composition, deoxyribonucleic acid-deoxyribonucleic acid hybridization, and biochemical studies were performed on some enterococci from clinical sources of uncertain taxonomic position. Our results indicate that 6 human strains, a single clinical isolate and a strain from bovine mastitis are genetically distinct from each other and all other previously described Enterococcus species and constitute three new species, for which the names Enterococcus raffinosus, Enterococcus solitarius and Enterococcus pseudoavium are proposed.

Abstract: The elongation factor Tu, encoded by tuf genes, is a GTP binding protein that plays a central role in protein synthesis. One to three tuf genes per genome are present, depending on the bacterial species. Most low-G+C-content gram-positive bacteria carry only one tuf gene. We have designed degenerate PCR primers derived from consensus sequences of the tuf gene to amplify partial tuf sequences from 17 enterococcal species and other phylogenetically related species. The amplified DNA fragments were sequenced either by direct sequencing or by sequencing cloned inserts containing putative amplicons. Two different tuf genes (tufA and tufB) were found in 11 enterococcal species, including Enterococcus avium, Enterococcus casseliflavus, Enterococcus dispar, Enterococcus durans, Enterococcus faecium, Enterococcus gallinarum, Enterococcus hirae, Enterococcus malodoratus, Enterococcus mundtii, Enterococcus pseudoavium, and Enterococcus raffinosus. For the other six enterococcal species (Enterococcus cecorum, Enterococcus columbae, Enterococcus faecalis, Enterococcus sulfureus, Enterococcus saccharolyticus, and Enterococcus solitarius), only the tufA gene was present. Based on 16S rRNA gene sequence analysis, the 11 species having two tuf genes all have a common ancestor, while the six species having only one copy diverged from the enterococcal lineage before that common ancestor. The presence of one or two copies of the tuf gene in enterococci was confirmed by Southern hybridization. Phylogenetic analysis of tuf sequences demonstrated that the enterococcal tufA gene branches with the Bacillus, Listeria, and Staphylococcus genera, while the enterococcal tufB gene clusters with the genera Streptococcus and Lactococcus. Primary structure analysis showed that four amino acid residues encoded within the sequenced regions are conserved and unique to the enterococcal tufB genes and the tuf genes of streptococci and Lactococcus lactis. The data suggest that an ancestral streptococcus or a streptococcus-related species may have horizontally transferred a tuf gene to the common ancestor of the 11 enterococcal species which now carry two tuf genes.

Abstract: Phylogenetic analysis of 16S rRNA gene sequences revealed that Enterococcus solitarius is not a member of the genus Enterococcus, but is related to species of the genus Tetragenococcus. On a phylogenetic tree, E. solitarius clustered with Tetragenococcus halophilus and Tetragenococcus muriaticus, with which it showed the highest 16S rRNA gene sequence similarity level (about 94%). Phenotypic studies indicated that E. solitarius was also unable to produce acid from lactose, providing further evidence of its affiliation to the genus Tetragenococcus. DNA hybridization studies indicated that E. solitarius was clearly a separate species, different from T. halophilus and T. muriaticus (reassociation levels of about 23 and 54%, respectively). As suggested in previous studies, E. solitarius is closely related to but clearly distinct from T. halophilus. Based upon properties that taxonomically distinguish it from species of the genus Enterococcus, it is proposed that E. solitarius be transferred to the genus Tetragenococcus and reclassified as Tetragenococcus solitarius comb. nov. (type strain, 885/78 T =ATCC 49428 T =CCUG 29293 T =CIP 103330 T =DSM 5634 T =JCM 8736 T =LMG 12890 T =NCTC 12193 T ).