Lactobacillaceae

The Lactobacillaceae are also the only family of the lactic acid bacteria which does not include pathogenic or opportunistic pathogenic organisms although some species, particularly Lacticaseibacillus rhamnosus and Weissella spp. can cause rare infections in critically ill patients.

With the exception of Lactococcus lactis, Streptococcus thermophilus and Tetragenococcus halophilus, most food fermenting lactic acid bacteria are now classified in the Lactobacillaceae.

The grandfathered term lactobacilli refers to all bacteria classified in Lactobacillaceae prior to 2020, i.e. Lactobacillus sensu lato (pre-split), Pediococcus, and Sharpea. Some authors use lactobacilli to refer to Lactobacillus sensu lato only.

Leuconostocaceae

At one point five genera (Convivina, Fructobacillus, Leuconostoc, Oenococcus and Weissella) were considered a separate family called Leuconostocaceae. These genera are non-spore-forming, round or elongated in shape, and anaerobic or aerotolerant. They usually inhabit nutrient-rich environments such as milk, meat, vegetable products, and fermented drinks. Lactic acid is the main end product of their characteristic heterofermentative carbohydrate metabolism. In 2020 Leuconostocaceae was synonymized with Lactobacillaceae.