Bacteroides multiacidus, a New Species from the Feces of Humans and Pigs

Abstract

Ninety-five strains of Bacteroides hypermegas Harrison and Hansen and of related organisms were isolated from the feces of humans, pigs, dogs, and chickens and were compared with three authentic strains of B. hypermegas. All isolates shared certain features in common: They were gram-negative, nonspore-forming, nonmotile, strictly anaerobic, stout rods which fermented a wide range of carbohydrates, had low final pH values in glucose broth (4.1 to 4.8), and were markedly stimulated by the presence of glucose in the medium. On the basis of a number of additional features, two distinct groups could be differentiated: 52 strains isolated from humans, chickens, and dogs were identical with B. hypermegas; the remaining 43 strains isolated from humans and pigs were considered to form a new species, for which the name Bacteroides multiacidus was proposed. B. multiacidus differs from B. hypermegas in that the former has the following: Smaller size of cell (0.8 to 1.5 μm by 3.0 to 20.0 μm); positive nitratase activity; low final pH value (4.1 to 4.3) in glucose broth; ability to produce major amounts of lactic and acetic acids with moderate amounts of succinic acid but no propionic acid from glucose; ability to grow in the presence of sodium propionate (15 mg/ml) as well as to ferment melezitose, dextrin, and starch; and higher guanine plus cytosine content in the deoxyribonucleic acid (56 to 58 mol %). The type strain of B. multiacidus is A 405-1 (= ATCC 27723 = NCTC 10934).