Sabri  M. Naser,  F. L. Thompson, B. Hoste, D. Gevers, K. Vandemeulebroecke, I. Cleenwerck, C. C. Thompson, M. Vancanneyt & J. Swings

The relatedness among ninety-one Enterococcus strains representing all validly described species was investigated by comparing a 1,102-bp fragment of atpA, the gene encoding the alpha subunit of ATP synthase. The relationships observed were in agreement with the phylogeny inferred from 16S rRNA gene sequence analysis. However, atpA gene sequences are much more discriminatory than 16S rRNA for species differentiation. All species were differentiated on the basis of atpA sequences with at maximum 92 % similarity. Six members of the E. faecium species-group (E. faecium, E. hirae, E. durans, E. villorum, E. mundtii, and E. ratti) show > 99% 16S rRNA gene sequence similarity, but only highest values of 89.9 % atpA gene sequence similarity were observed. Intraspecies sequence similarities were for all species varying between 98.6 to 100 % atpA sequence similarity, except for E. faecium strains with a lower value of 96.3 %. Our data clearly show that atpA provides an alternative tool for phylogenetic study and identification of enterococci.