Once upon a time, I chanced upon an old microbiology book that detailed the rather colorful world of enterobacteria. Salmonella in particular stood out, as it seemed there were a lot of species: typhi / typhosa, paratyphi, gallinarum, typhimurium, choleraesuis, and quite a bunch of others that I have now forgotten.
Flipping through a newer book, it now seems that all of these "species" were collated under choleraesuis (and now more recently enterica), with all those species being demoted to "strains" (or maybe I should use the current term of art, "serovar"). Unfortunately, the book didn't give much in the way of explaining about this merger.
So, why is there now only S. enterica? If "S. typhi" is a mere serovar, how come the species name is still used in the literature?