Numerical Taxonomy of Saccharolytic Clostridia, Particularly Clostridium perfringens-Like Strains: Descriptions of Clostridium absonum sp. n. and Clostridium paraperfringens
Clostridium perfringens-like strains whose taxonomic position is uncertain were examined in detail. The lecithinases of these strains exhibited less avidity to the alpha-antitoxin of C. perfringens than did the C. perfringens lecithinase. On the basis of a computer analysis, the C. perfringens-like strains were grouped into two phenons, I and III, both of which are distinctly separable from C. perfringens (phenon II). Strains previously identified by us as belonging to Clostridium paraperfringens Nakamura et al. 1970, including strain G (= ATCC 27639), here designated as the type strain of C. paraperfringens, were found to belong to phenon I, and the strains of phenon III are regarded as constituting a new species, for which we propose the name Clostridium absonum. The type strain of C. absonum is HA-7103 (= ATCC 27555). The main characters differentiating C. absonum from C. perfringens are as follows: C. absonum produces a lecithinase which exhibits extremely low avidity to C. perfringens alpha-antitoxin, rapidly ferments salicin, does not ferment raffinose, and does not liquefy 10% gelatin; the main characters of C. absonum which differentiate it from phenon I strains are: Larger cell width, a distinctly stronger lecithinase reaction, liquefaction of 2% gelatin, production of butanol, and weak toxicity for mice. Deoxyribonucleic acid (DNA)-DNA homology studies of phenons I, II, and III confirmed the validity of the above-mentioned groupings. A computer analysis of other saccharolytic clostridia revealed that C. butyricum, C. acetobutyricum, and C. multifermentans are associated by similarity values higher than 90% and that C. septicum and C. chauvoei constitute separate, but closely related, taxa.