The genera of lactic acid bacteria

According to current taxonomy, the lactic acid bacteria group consists of twelve genera (Table 2-2). All are in the phylum Firmicutes, Order, Lactobacillales. Based on 16S rRNA sequencing and other molecular techniques, the lactic acid bacteria can be grouped into a broad phy-logenetic cluster, positioned not far from other low G + C Gram positive bacteria (Figure 2-2). Five sub-clusters are evident from this tree, including: (1) a Streptococcus-Lactococcus branch (Family Streptococcaceae), (2) a Lactobacillus branch (Family Lactobacillaceae), (3) a separate Lactobacillus-Pediococcus branch (Family Lactobacillaceae); (4) an Oenococcus-Leuconostoc-Weisella branch (Family Leu-conostocaceae), and (5) a Carnobacterium-Aerococcus-Enterococcus-Tetragenococcus-Vagococcus branch (Families Carnobacteri-aceae, Aerococcaceae, and Enterococcaceae).

It is worth noting that this phylogeny is not entirely consistent with regard to the morphological and physiological characteristics of these bacteria. For example, Lactobacillus and Pediococcus are in the same sub-cluster, yet the former are rods and include heterofermenta-tive species, whereas the latter are homofer-menting cocci. Likewise, Carnobacterium are obligate heterofermentative rods, and Entero-coccus and Vagococcus are homofermentative cocci.

Seven of the twelve genera of lactic acid bacteria, Lactobacillus, Lactococcus, Leucon-ostoc, Oenococcus, Pediococcus, Streptococcus, and Tetragenococcus, are used directly in food fermentations. Although Enterococcus sp. are often found in fermented foods (e.g., cheese, sausage, fermented vegetables), except for a few occasions, they are not added directly. In fact, their presence is often undesirable, in part, because they are sometimes used as indicators of fecal contamination and also because some strains may harbor mobile antibiotic-resistance genes.

Importantly, some strains of Enterococcus are capable of causing infections in humans. Likewise, Carnobacterium are also undesirable, mainly because they are considered as

Staphylococcus aureus

Lactobacillus delbrueckii

Lactobacillus johnsonii Lactobacillus gasseri

Bacillus subtilis Tetragenococcu^halophilus Listeria monocytogenes

Enterococcus faecalis

Vagococcus salmoninarum

Carnobacterium funditum

Aerococcus viridans

Oenococcus oeni

Lactobacillus plantarum

Pediococcus pentosaceus

Lactobacillus brevis Lactobacillus casei

Clostridium botulinum

Staphylococcus aureus

Lactobacillus delbrueckii

Lactobacillus plantarum

Pediococcus pentosaceus

Lactobacillus brevis Lactobacillus casei

Bacillus subtilis Tetragenococcu^halophilus Listeria monocytogenes

Enterococcus faecalis

Vagococcus salmoninarum

Carnobacterium funditum

Aerococcus viridans

Oenococcus oeni

Vagococcus Salmoninarum

Leuconostoc mesenteroides

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