Variable Sugar Fermentation by Clostridia

AbstractForty‐two sugar fermentation characteristics recorded as “d” in the 8th edition of Bergey's Manual of Determinative Bacteriology were reinvestigated by using eight different peptone media and 205 strains of nine species of pathogenic Clostridia. In the absence of sugar, the final pH of 7‐day cultures in the basal medium varied widely depending on the peptone employed, the species tested, and even the strain of the species. In the presence of sugar, the final pH of 7‐day cultures was markedly influenced by these factors. Since the sugars with reactions recorded as “d” were weakly fermented and, consequently, the fermentation reactions were easily affected by cultural variations resulting in strain instability, we employed the pH difference method (ΔpH method) in which the pH difference of 0.5 between cultures with and without sugar was used as the critical level. Thirty‐six (86%) of the 42 sugar reactions recorded as “d” were sorted into “+” or “‐” by the ΔpH method. Six sugars, however, still remained as “d” because of their extremely weak fermentation characters. The use of the ΔpH method in any peptone medium not only minimizes incorrect evaluation but also can provide so