Lactobacillus acidophilus

Lactobacillus acidophilus is a lactic-acid bacterium: a short, Gram-positive rod that is homofermentative and grows best at around 37–42 °C. It was first isolated by Moro in 1900, and it is among the least oxygen-tolerant of the lactobacilli.^[3]

In 2020 the very large genus Lactobacillus was reclassified into 25 genera on the basis of whole-genome comparisons. Lactobacillus acidophilus was one of the species that kept its name: it stays in the narrowed (“emended”) genus Lactobacillus, alongside other species adapted to living with vertebrate hosts. So, unlike several of its old genus-mates, its name has not changed.^[1],[2]

The 2020 reclassification groups Lactobacillus acidophilus with lactobacilli that are host-adapted — species that live in association with vertebrate animals rather than in plants or the wider environment.^[1]

Lactobacilli are important inhabitants of the gastrointestinal tract. L. acidophilus belongs to the “acidophilus complex”, a group of closely related species that have historically been isolated from the gut of humans and animals; the species itself was first isolated from infant faeces.^[3]

Particular strains have also been produced commercially for decades — the well-known strain NCFM, for example, since 1972.^[3]

Lactobacillus acidophilus is described as the most widely recognised and commercially distributed probiotic culture, and species of Lactobacillus and Bifidobacterium are the most commonly used probiotics in human medicine.^[3],[4]

The European Food Safety Authority (EFSA) considers the species suitable for its “qualified presumption of safety” (QPS) approach. In 2018 EFSA’s feed panel assessed one particular strain (CECT 4529) as a feed additive for cats and dogs, in the category of zootechnical additives, functional group “gut flora stabilisers”. That assessment applies to that strain only: probiotic benefits are generally considered strain-specific.^[5],[6]

One sequenced strain’s genome includes gene clusters for transporting a range of carbohydrates, including fructooligosaccharides. Fructooligosaccharides also appear on our label, as inulin from chicory root.^[3]

Lactobacillus acidophilus strains have also been studied in dogs, and appear among the products included in a 2019 systematic review of probiotic studies in dogs published in the Journal of Veterinary Internal Medicine.^[4]

The label lists the strain in the Live Culture Blend — five strains that together provide 2 billion CFU per tablet. The label states that total for the whole blend only; it does not give a separate CFU count for each strain, so we don’t either. You’ll find it named first in the blend on every bottle of DIGEST+.