Comparison of biochemical and genotypic speciation methods for vancomycin-resistant enterococci isolated from urban wastewater treatment plants

Enterococci species in wastewater including Enterococcus faecalis, Enterococcus faecium, Enterococcus casseliflavus and Enterococcus gallinarum isolates (n = 308) with low or high level vancomycin resistance were determined and compared using a phenotypic method (RapID (TM) STR system), 16S rRNA sequencing, and multi-locus (atpA, groESL, and pheS) sequence analysis (MLSA). Error rates for the RapID (TM) STR system were E. faecalis (15.9%), E. faecium (21.5%), and E. casseliflavus/E. gallinarum (56.9%) when referenced to the consensus of all methods tested. Comparison of single nucleotide polymorphism (SNP) distances and phylogenetic trees suggested that the groESL locus delineated species more effectively than other loci. The groESL locus was the most reliable loci for the correct identification of Enterococcus spp., including E. casselifiavus and E. gallinarum, with high congruence compared to the consensus (Adjusted Rand Index = 0.954; Adjusted Wallace Co-efficient = 0.941). All of the methods were compared to whole genome sequencing, which acted as a gold standard, for the isolates from this study and those downloaded from NCBI.