This document records the proceedings of the International Committee on Systematics of Prokaryotes Subcommittee on Gram-negative anaerobic rods, held July 9-10, 2000, in Manchester, UK. The subcommittee discussed critical issues in prokaryotic taxonomy, including the need for polyphasic approaches beyond 16S rRNA sequencing alone when classifying new species. Members expressed concern that recent taxonomic proposals relied solely on genetic data without adequate phenotypic support. The committee reviewed the state of phenotypic identification methods, noting that traditional biochemical tests remain time-consuming while commercial systems inadequately identify anaerobes to the species level. A checkerboard DNA-probe assay was presented as an alternative for rapid, quantitative detection of fastidious bacteria in clinical samples. The subcommittee examined taxonomic reorganization of major Bacteroides subdivisions into distinct genera including Prevotella and Porphyromonas, which were supported by 16S rRNA analysis. Updates were provided on pigmented and non-pigmented anaerobic species, the Fusobacterium-Leptotrichia group phylogeny, and ongoing Leptotrichia classification studies using combined molecular and biochemical approaches.

Key findings

• Polyphasic taxonomy combining genetic, phenotypic, and chemotaxonomic data is essential; 16S rRNA sequencing alone is insufficient for reliable species classification
• Phenotypic identification methods need improvement; traditional tests are time-consuming while commercial systems remain inadequate for anaerobic bacteria
• Checkerboard DNA-probe assay enables rapid detection and quantitation of fastidious, slow-growing gram-negative anaerobes without culturing
• 16S rRNA phylogenetic analyses support the earlier subdivision of genus Bacteroides into Bacteroides sensu stricto, Prevotella, and Porphyromonas based on biochemical and chemotaxonomic criteria
• Discordance exists between 16S rDNA sequencing and phenotypic test results, highlighting the importance of integrating multiple taxonomic approaches