Lactobacillus is a genus of Gram-positive, aerotolerant anaerobes or microaerophilic, rod-shaped, non-spore-forming bacteria. Until March 2020, the genus Lactobacillus comprised over 260 phylogenetically, ecologically, and metabolically diverse species; a taxonomic revision of the genus in 2020 assigned lactobacilli to 25 genera.

Lactobacillus species constitute a significant component of the human and animal microbiota at a number of body sites, such as the digestive system, and the female genital system.[4] In women of European ancestry, Lactobacillus species are normally a major part of the vaginal microbiota.[5][6] Lactobacillus forms biofilms in the vaginal and gut microbiota, allowing them to persist during harsh environmental conditions and maintain ample populations.

Lactobacillus exhibits a mutualistic relationship with the human body, as it protects the host against potential invasions by pathogens, and in turn, the host provides a source of nutrients. Lactobacilli are among the most common probiotic found in food such as yogurt, and it is diverse in its application to maintain human well-being, as it can help treat diarrhea, vaginal infections, and skin disorders such as eczema.

Below the post, Pritish Kumar discusses Lactobacillus a bacteria that is present inside the human body:


Lactobacilli are homofermentative, i.e. hexoses are metabolised by glycolysis to lactate as major end product, or heterofermentative, i.e. hexoses are metabolised by the Phosphoketolase pathway to lactate, CO2 and acetate or ethanol as major end products. Most lactobacilli are aerotolerant and some species respire if heme and menaquinone are present in the growth medium. Aerotolerance of lactobacilli is manganese-dependent and has been explored (and explained) in Lactiplantibacillus plantarum (previously Lactobacillus plantarum). Lactobacilli generally do not require iron for growth.

The Lactobacillus are the only family of the lactic acid bacteria (LAB) that includes homofermentative and heterofermentative organisms; in the Lactobacillus, homofermentative or heterofermentative metabolism is shared by all strains of a genus. Lactobacillus species are all homofermentative, do not express pyruvate format lyase, and most species do not ferment pentoses. In L. crispatus, pentose metabolism is strain specific and acquired by lateral gene transfer.


The genus Lactobacillus comprises the following species:

Lactobacillus acetotolerans

Lactobacillus acidophilus

“Lactobacillus alvi”

Lactobacillus amylolyticus Bohak

Lactobacillus amylovorus

Lactobacillus apis

“Lactobacillus backi”

Lactobacillus bombicola

Lactobacillus colini

Lactobacillus crispatus

Lactobacillus delbrueckii

Lactobacillus equicursoris

Lactobacillus fornicalis

Lactobacillus gallinarum

Lactobacillus gasseri

Lactobacillus gigeriorum

3D rendering Bacteria closeup.

Human health

Vaginal tract

The female genital tract is one of the principal colonization sites for human macrobiotic, and there is interest in the relationship between their presence and human health, with a domination by a single species being correlated with general welfare and good outcomes in pregnancy. In around 70% of women, a Lactobacillus species is dominant, although that has been found to vary between American women of European origin and those of African origin, the latter group tending to have more diverse vaginal microbiota. Similar differences have also been identified in comparisons between Belgian and Tanzanian women.


Fermented bacteria like lactic acid bacteria (LAB) produce hydrogen peroxide which protects themselves from oxygen toxicity. The accumulation of hydrogen peroxide in growth media, and its antagonistic effects on Staphylococcus aureus and Pseudomonas, have been demonstrated by researchers. LAB cultures have been used as starter cultures to create fermented foods since the beginning of the 20th century.

Oral health

Some lactobacilli have been associated with cases of dental caries (cavities). Lactic acid can corrode teeth, and the Lactobacillus count in saliva has been used as a “caries test” for many years. Lactobacilli characteristically cause existing carious lesions to progress, especially those in coronal caries. The issue is, however, complex, as recent studies show probiotics can allow beneficial lactobacilli to populate sites on teeth, preventing streptococcal pathogens from taking hold and inducing dental decay.