The Conundrum
For the clinical and public health microbiologist, the rapid increase
in the number of proposed genera and species has been a formidable
challenge in keeping up to date with taxonomic changes. From 1993
to 2000, the average number of newly proposed bacterial species
was around 200 per year. Notably, however, of the estimated 7,300
known bacterial species, over 70% have been described since 2000.
This is no doubt due to the explosion in 16S rRNA gene sequences
reported in public and private databases, along with the analysis of
other housekeeping genes, such as rpoB, dnaJ, and recA. This
upsurge in new taxa described has been further coupled to the following
facts: (i) as originally noted by Frederiksen, Magee, and Ursing
(6), the number of newly described species/subspecies based
upon a single strain was 43% in 1998, and that trend has continued
even to today; (ii) the vast majority of bacterial species described
(80% to 90%) have been isolated only from environmental sites,
often from unusual habitats (air conditioning systems, seawater,
insect guts, plant roots, or fruit); and, finally, (iii) it is often not clear
whether a newly described bacterial species originating from a
clinical sample is associated with causing human disease. These confounding
facts are further exacerbated by the naming, renaming,
and renaming again of the same bacterial species (7).