Identification of enterococci from broiler products and a broiler processing plant and description of Enterococcus viikkiensis sp. nov

Abstract

In two previous studies dealing with lactic acid bacteria (LAB) from modified-atmosphere-packaged (MAP) broiler products and a broiler processing plant, several isolates remained unidentified. According to 16S rRNA gene sequence analysis, 36 isolates were assigned to the genus Enterococcus. Numerical analysis of combined HindIII and EcoRI ribopatterns of these isolates resulted in species-specific clusters that were congruent with the clusters obtained by both DNA-directed RNA polymerase subunit A (rpoA) and phenylalanyl-tRNA synthetase α chain (pheS) housekeeping gene analyses. In the analyses, a group of five isolates distinct from any known enterococcal species clustered together. The five isolates were positioned in the Enterococcus avium group, with E. devriesei being the closest phylogenetic neighbor. The DNA-DNA hybridization levels with E. devriesei ranged from 28.8 to 54.3% and indicated that these strains represented a novel species. The name Enterococcus viikkiensis sp. nov. is proposed, with strain DSM 24043(T) (LMG 26075(T)) being the type strain. Our study demonstrated that the identification of enterococci within the E. avium phylogenetic group demands polyphasic taxonomic approaches. The rpoA and pheS gene similarities (99.0 to 99.2% and 94.3 to 95.4%, respectively) between E. viikkiensis and its closest phylogenetic neighbor, E. devriesei, were higher than those previously reported within the enterococci. In addition, the phenotypic profiles of the species in the E. avium group were also highly similar, and some traits were found to be misleading for enterococci, such as E. viikkiensis does not grow at 45°C. The numerical analysis of combined HindIII and EcoRI ribopatterns was of considerable assistance in distinguishing enterococcal species within the E. avium group.

FIG. 1.

UPGMA dendrogram based on combined HindIII and EcoRI ribopatterns of 31 Enterococcus type and reference strains and 36 isolates from MAP broiler products and a broiler processing plant. The HindIII and EcoRI banding patterns are also shown. The molecular masses of the bands range from 1 kb (right side) to 23 kb (left side).

FIG. 2.

Neighbor-joining dendrogram based on the rpoA sequences of 12 Enterococcus type and reference strains and 17 isolates from MAP broiler products and a broiler processing plant positioned in the E. avium phylogenetic group. Bootstrap percentages (≥50%) after 500 replicates are shown. Tetragenococcus solitarius is included as an outgroup.

FIG. 3.

Neighbor-joining dendrogram based on the pheS sequences of 12 Enterococcus type and reference strains and 14 isolates from MAP broiler products and a broiler processing plant positioned in the E. avium phylogenetic group. Bootstrap percentages (≥50%) after 500 replicates are shown. Tetragenococcus solitarius is included as an outgroup.