The genus Bacterium was a taxon described in 1828 by Christian Gottfried Ehrenberg. The type species was later changed from Bacterium triloculare to Bacterium coli (now Escherichia coli) as it was lost. In 1951 and then in 1954 it was recognised as a nomen generum rejiciendum, which means a generic name to be rejected, this also applied to its family Bacteriaceae. This genus included non-spore forming rods whose relation to other species was obscure (a "taxonomy dumping group"). This is different from the genus Bacillus, whose members were spore forming rods (sensu Cohn 1872).