Strains of ‘Streptococcus pluton’ isolated from honeybee larvae with European foul-brood from widely separate parts of the world represent a relatively homogeneous taxon; all are related serologically. Added cysteine or cystine make a variety of otherwise unsuitable nitrogen sources satisfactory for all strains, which all have the same fastidious culture requirements. Test strains lack respiratory quinones and possess a Group A peptidoglycan based upon lysine, primarily straight-chain and cyclopropane-ring fatty acids, and a DNA base composition of 29–30 G + C mol %. Results obtained indicate that the strains presently designated ‘Strep. pluton’ should constitute the nucleus of a new genus.