Comparison of phenotypic and genotypic taxonomic methods for the identification of dairy enterococci

Abstract

The purpose of the study was to assess the phenotypic and genotypic taxonomic congruence in order to allow species allocation of dairy enterococci. A total of 364 enterococci isolated from ewes'milk and cheese from four Portuguese Registered Designation of Origin areas and 25 type and reference strains of Enterococcus spp. were characterized by a polyphasic taxonomical approach involving 40 physiological and biochemical tests, whole-cell protein profiles, amplification of 16S-23S intergenic spacer regions (ITS-PCR) and subsequent restriction analysis (ARDRA). Ribotyping was also performed with reference strains and a subset of 146 isolates. Numerical hierarchic data analysis showed that single-technique identification levels increase from the physiological and biochemical tests to the protein approach, being lower with ITS/ARDRA and ribotyping. Cross-analysis confirmed a higher unmatching level in all pairwise combinations involving physiological and biochemical data. Whole-cell protein profiles followed by ITS/ARDRA identified 89% of the enterococci. Reliable identification of enterococci from milk and cheese could be obtained by analysis of whole-cell protein profiles. ITS-PCR can be used to confirm E. durans and E. faecium and ARDRA further confirms E. faecalis. Results revealed E. faecalis, E. durans, E. hirae and E. faecium as the prevalent species, although species prevalence showed some degree of variation among the areas.