Résumé
The family Veillonellaceae belongs to the phylum Firmicutes, the class Negativicutes, and the order Selenomonadales. Delineation of the family was established in 2010 on the basis of 16S rRNA gene phylogenetic analyses, and to date, the family includes 6 genera of Gram-negative, anaerobic, or microaerophilic cocci and coccobacilli and 25 species, i.e., the genera Veillonella (12 species), Megasphaera and Dialister (5 species each), Allisonella, Anaeroglobus, and Negativicoccus (1 species each). The most striking particularity of this family, and more generally of the class Negativicutes, is to group bacteria with Gram-negative cell wall structure within a phylum of Gram-positive bacteria. Genera can be distinguished based on their phenotypic, genetic, genomic, and phylogenetic characteristics, while molecular-based methods may be required for species affiliation, particularly in the genus Veillonella. The isolates displayed various resistance patterns to antimicrobial agents. The family includes three beer-spoilage species belonging to the genus Megasphaera, other species being representatives of several human and other animal microbiotae, and some of them can act as opportunistic pathogens for animals including humans being usually responsible for polymicrobial infections and more rarely for monomicrobial severe infections like osteoarticular infections or endocarditis.