Related Genera Within the Family Bifidobacteriaceae

Within the class of Actinobacteria, Stackebrandt et al. (1997) proposed the new order Bifidobacteriales with the family Bifidobacteriaceae as type family of the order. At that time only two genera were described to be members of the Bifidobacteriaceae (i.e., the genus Bifidobacterium as a type genus and the genus Gardnerella). Following the new classification system, phylogenetically closely related genera are clustered into the family Bifidobacteriaceae on the basis of 16S rRNA/DNA sequences analysis; this is of paramount importance in the new taxonomic vision if compared to the more traditional chemotaxonomic, morphological, and physiological properties. In the following years the family Bifidobacteriaceae was expanded so that at present in addition to Bifidobacterium (Orla-Jensen, 1924) with 54 validated species and ten subspecies, and Gardnerella (Greenwood and Pickett, 1980) with the species Gardnerella vaginalis, another seven genera were allocated in the family. This chapter will be devoted to the so-called scardovial genera, since the genus Bifidobacterium will be treated in a separate chapter while the genus Gardnerella is marginal for the scope of the present book and is already well represented in the literature. The new taxa belonging to the scardovial genera were isolated from a variety of habitats: Aeriscardovia aeriphila from a porcine cecum, Alloscardovia omnicolens from human clinical samples, Alloscardovia macacae from the milk of a macaque, Alloscardovia criceti from dental plaque of golden hamsters, Bombiscardovia coagulans from the digestive tract of bumblebees, Neoscardovia arbecensis from porcine slurries, Parascardovia denticolens from human dental caries, Pseudoscardovia suis and P. radai from the digestive tract of wild pigs, Scardovia inopinata from human dental caries, and S. wiggsiae from a wound infection in the arm of an intravenous drug user. Considering the use of beneficial bacteria in different applications, one aspect of great importance refers to their classification into risk groups. Most countries use a four-level risk group system according to their virulence and potential danger to humans. Almost all the species belonging to scardovial genera are classified in risk group 1 that refers to organisms that generally do not cause disease in healthy adult humans. Only Alloscardovia omnicolens is classified into risk group 2, which refers to microorganisms with a moderate risk for humans. The data on the risk level were obtained from Deutsche Sammlung von Mikroorganismen und Zellkulturen and are partially based on the list from Technical Rules for Biological Agents. Within the family Bifidobacteriaceae the major genera include Bifidobacterium and Gardnerella. Bifidobacteria are playing an important role in the development of new concepts related to beneficial bacteria found in human and animal intestinal tracts. Their use in food and pharmaceutical preparations as probiotics is a fast-growing business. Gardnerella vaginalis is the only species of this genus. Isolated from the human genital and urinary tracts, it is classified in risk group 2. For a long time it has been considered as the etiological agent of bacterial vaginosis. Nowadays it is assumed that bacterial vaginosis is associated with a large spectrum of anaerobic bacteria. The role of G. vaginalis in this disease is controversial, as demonstrated in recent studies that demonstrated a high rate of detection of G. vaginalis in subjects without bacterial vaginosis (Fredricks et al., 2007).