Some cases of late-onset (regressive) autism may involve abnormal flora because oral vancomycin, which is poorly absorbed, may lead to significant improvement in these children. Fecal flora of children with regressive autism was compared with that of control children, and clostridial counts were higher. The number of clostridial species found in the stools of children with autism was greater than in the stools of control children. Children with autism had 9 species of Clostridium not found in controls, whereas controls yielded only 3 species not found in children with autism. In all, there were 25 different clostridial species found. In gastric and duodenal specimens, the most striking finding was total absence of non-spore-forming anaerobes and microaerophilic bacteria from control children and significant numbers of such bacteria from children with autism. These studies demonstrate significant alterations in the upper and lower intestinal flora of children with late-onset autism and may provide insights into the nature of this disorder.

It was recently proposed that the genus Bacteroides should be restricted to Bacteroides fragilis (the type species) and closely related organisms (viz., B. caccae, B. distusonis, B . eggerthii, B . merdae, B . ovatus, B. stercoris, B . thetaiotaomicron, B . unifomtis, and B. vulgatus). By contrast, the moderately saccharolytic, predominantly oral Bacteroides species, which include B . melaninogenicus, B. oralis, and related species, form a phenotypically and phylogenetically coherent group of species which differ so significantly from the emended description of the genus Bacteroides that they should not be classified in the same genus. Therefore, we formally propose that these species be reclassified in a new genus, Prevotella. The type species is Prevotella melaninogenica.The genus Bacteroides has recently undergone major taxonomic revision (32,46,47). It is now universely accepted that this genus is phenotypically and phylogenetically heterogeneous. Several new genera, most of which are monospecific, have recently been proposed to accomodate some of the atypical members of the group (Table 1). The majority of the more typical members of the genus (particularly those associated with humans) form three broad groups on the basis of their ability to ferment carbohydrates (viz., saccharolytic, moderately saccharolytic, and asaccharolytic groups of species [for example, see references 17 and 19). The first group consists of Bacteroides fragilis and related species which are generally isolated from gastrointestinal tracts (lo), whereas the second group comprises a large number of moderately saccharolytic species and includes B . melaninogenicus, B. oralis, and related species. The third group includes the pigmented, asaccharolytic species B. asaccharolyticus and B. endodontalis and the important periodontal pathogen B. gingivalis (8,33,34,53). The recognition of three major groups within the genus Bacteroides is supported by biochemical (6,17,27,40,44) and rRNA cistron similarities (19).It has recently been proposed that the genus Bacteroides be restricted to highly fermentative species that phenotypically resemble B. fragilis, the type species of the genus (47), and include B. caccae, B. distasonis, B. eggerthii, B. merdae, B. ovatus, B. stercoris, B. thetaiotaomicron, B. uniformis, and B. vulgatus. Similarly, a new genus, Porphyromonas, has been created to provide a niche for the asaccharolytic species mentioned above (46). However, the position of the moderately saccharolytic species that do not grow well in 2% oxgall remains unresolved. Most species of this group are indigenous to oral cavities (17,33,34), and several (B. corporis, B. intermedius, B. loescheii, B. melaninogenicus, and some strains qf B. denticola [16, 171) produce pigmented colonies on blood agar. The nonpigmented members of this group are B. bivius, B. buccae, B. buccalis, B. disiens, B. heparinolyticus, B . oralis, B. oris, B. oulorum, B. ruminicola, B. veroralis, and B. zoogleoformans. Phenotypically, these species are all similar and can b...

The asaccharolytic, pigmented Bacteroides, Bacteroides asaccharolyticus, Bacteroides gingivalis, and Bacteroides endodontalis, form a group of relatively homogeneous species which differ markedly in biochemical and chemical properties from the type species of Bacteroides, Bacteroides fragilis (Castellani and Chalmers), such that they should not be retained within this genus. Therefore, we propose that Bacteroides asaccharolyticus (Holdeman and Moore) Finegold and Barnes, Bacteroides gingivalis Coykendhll, Kaczmarek and Slots, and Bacteroides endodontalis van Steenbergen, van Winkelhoff, Mayrand, Grenier and de Graaff be reclassified in a new genus, Porphyromonas, as Porphyromonas asaccharolytica comb. nov., Porphyromonas gingivalis comb. nov., and Porphyromonas endodontalis comb. nov., respectively.In Bergey 's Manual of Determinative Bacteriology, 8th ed. (12), the asaccharolytic, pigmented Bacteroides were regarded as a single homogeneous taxon, Bacteroides melaninogenicus subsp. asaccharolyticus. As the clinical significance of these microorganisms in oral cavities was recognized, extensive taxonomic studies were carried out. Heterogeneity was first demonstrated among these bacteria through studies of their deoxyribonucleic acid (DNA) base compositions and enzyme polymorphism, and two regions of variation were reported (29). These findings were substantiated by sodium dodecyl sulfate polypeptide patterns (34) and DNA-DNA hybridization data (36). As a result of these studies on the asaccharolytic, pigmented strains, the group containing strains with high guanine-plus-cytosine (G+C) contents (52 to 54 mol%) and an electrophoretically fastmigrating malate dehydrogenase (MDH) was reclassified as a new species, Bacteroides asaccharolyticus (7, 29). Further differences between B. asaccharolyticus and the group of strains with low G+C contents (46 to 48 mol%) and a slow-migrating MDH (29) were revealed by an analysis of tlheir lipids (26). Strains of B. asaccharolyticus possess very high levels of 13-methyl-tetradecanoic acid (iso-C,,,, acid) and menaquinones with 10 isoprene units (MK-lo), whereas tlhe group of strains with low G+C contents contains significantly lower levels of iso-C,,:, fatty acids and menaquinones with nine isoprene units (MK-9) (26). The latter group of strains was subsequently reclassified as Bacteroides gingivalis (4). It is generally believed that most oral, asaccharolytic, black-pigmented Bacteroides strains belong to B. gingivalis, whereas most nonoral or clinical isolates are B. asaccharolyticus strains. Recently, a third asaccharolytic species, Bacteroides endodontalis, which was isolated from infected dental root canals, has been proposed (37). Phenotypically, B. endodontalis appears to be more closely related to B. asaccharolyticus than to B. gingivalis and possesses a DNA base composition of ca. 50 to 51 mol% G+C (37). The MDH of B. endodontalis migrates faster than the MDHs of B. asaccharolyticus and B. gingivalis (Shah, unpublished data).B. asaccharolyticus, B. gingivalis, and B. en...