Taxonomy of Spiral and Curved Clostridia

Abstract

Seventy seven curved and helically coiled, anaerobic bacilli, which were isolated from the intestinal contents of humans, rabbits and chickens, were the subject of this study. Because they were anaerobic, spore forming, Gram positive rods the isolates were identified as clostridia. Those strains which seemed to have a helically coiled cellular conformation were in fact microcolonies of semicircular cells joined end to end. The strains fell into five groups on the basis of their biochemical characteristics, their susceptibilities to a range of antimicrobial agents, their outer membrane protein and extracellular toxins. Group 1 contained three strains of Clostridium spiroforme, including the type strain, isolated from healthy humans who had not been receiving antibiotics. None of these isolates produced a toxin. Although similar in some respects to the members of Groups 2 and 3, they do in fact represent a distinct group. Groups 2 and 3 share some common extracellular antigens. The former consists of three strains of C. spiroforme isolated from diarrhoeic humans who had received clindamycin, the latter was made up of 59 strains of C. spiroforme from scouring rabbits. All of the rabbit strains, but none of the human isolates, produced a lethal toxin neutralizable with C. perfringens iota antitoxin. Group 4 contained six unnamed strains isolated from healthy chickens. None were toxigenic. They differed in most aspects from the C. spiroforme strains but did share some properties with C. cocleatum, the organism represented in group 5. It is not yet clear whether or not group 2 and 3 should be given species status separate from C. spiroforme. For the time being, however, we are continuing to refer to them as C. spiroforme.