Lactobacillus is a household name when it comes to bacteria and refers to a type of healthy bacteria that live in our digestive, urinary, and genital systems without causing disease. These bacteria are frequently seen on the labels of probiotics and are present in popular fermented foods. But what is their role and how do they support our health and skin care?
A day in the life of Lactobacillus
Lactobacillus bacteria play an important role in human health and are considered VIP members of a balanced and healthy gut microbiome. This bacterial group is very well known amongst lovers of live yoghurt and probiotic devotees alike.
They reside in and on most of us from birth – bacteria from this genus have even been found in breast milk . (See our maternal microbiome basics to read more on the topic.)
At the beginning of the 20th century, Martinus Beijerinck first identified the species Bacillus acidophilus (now known as Lactobacillus acidophilus), isolated from the human gut. Since then, Lactobacillus species have been found living in a wide variety of different habitats and hosts .
Most are found living with other Lactobacillus species. For example, at least ten different strains of Lactobacillus were found coexisting in Chinese traditional pickle and yoghurt . In fact, nineteen strains of Lactobacillus were recently isolated from the International Space Station and its resupply vehicle .
But what do these bacteria actually do? Well, the name Lactobacillus gives an indication of their function: they produce lactic acid and thus belong to the Lactic Acid Bacteria (LAB) group, which encompasses many other types of bacteria which share this common trait. They are beneficial to human health as they help us break down food, absorb nutrients, and outcompete organisms that might cause illness.
Lactobacillusspecies can be divided into two types based on how they metabolise sugars:
- Homofermentative species ferment more than 90% of sugar (glucose) to lactic acid and they do not produce gas.
- Heterofermentative species, on the other hand, ferment sugar into not only lactic acid but other substances such as acetic acid. They also produce CO2 gas (like humans!).
While the LAB group is a vast and mixed group, all of these bacteria share common metabolic – such as requiring a fermentable carbohydrate for growth – and physiological characteristics.
LAB and the gut microbiome
The Lactic Acid Bacteria (LAB) are crucial members of the gut microbiome ecosystem and they play an integral role in the digestion of our food and gut health. Some LAB species also produce acetic acid, thus play an important role in regulating the pH of the gut to encourage healthy bacteria species to thrive whilst creating a hostile environment for pathogenic species.
LAB species are amongst the most prominent gut microbes. The most common gut LAB species are Streptococcus thermophilus and Lactococcus lactis, both of which are also found in breast milk, as well as in fermented dairy products.
Increasingly-popular fermented foods are made using LAB – think Kefir, live yoghurt, and sauerkraut. LAB are also used to preserve and pickle foods. Even salami production involves cultures of several Lactobacillus species! (For more on microbiome-friendly foods see our recent article with nutritionist Laura Tilt.)
However, there is contention as to whether ingested LAB succeed in becoming members of the gut microbiome. In other words, do the beneficial bacteria in the probiotic food we eat reach our gut?
In a 2017 article, ‘Do Probiotics Really Work?’, the author suggested that strains of Bifidobacterium or Lactobacillus species in many yogurts and probiotic products may not be the same kind that can survive the highly acidic human stomach and go on to colonize the gut .
However, a recent genome-based study by Pasolli et al  examining the differences between food and gut LAB microbes linked LAB from food with LAB living in the gut microbiome. The researchers showed that some LAB strains in fermented foods are closely related to LAB strains in the gut, strongly suggesting that these strains of LAB did survive the highly acidic human stomach to colonize the gut.
LAB and probiotic cosmetics
Lactobacillus species, along with other LAB bacteria, are found living at low levels on skin. Besides creating a local acidic environment, Lactobacillus species influence the microbiome by producing biofilms (a thin layer containing bacteria which stick to the surface), providing nutrients, and by releasing bacteriocins (proteins with antimicrobial properties) that help prevent potential pathogenic (harmful) bacteria from becoming established.
Long before the gut and skin microbiome were considered as a target for food and cosmetics, people enjoyed eating live yoghurt and using it on their bodies and faces to moisten and brighten skin. As our understanding of the human microbiome increases, so does the interest (and hope) for live bacteria skin care products.
The need to maintain a live cosmetic product’s integrity throughout its shelf-life is the biggest challenge in meeting this ambition. New products with live bacteria must pass the (perhaps aptly named) challenge testing for product safety and for it to conform to international cosmetic regulations. There are some pioneering companies selling live skin care. For example, Mother Dirt’s products are said to contain 3+ billion colony forming units (a measurement of the concentration of microbes) in every bottle – note this is talking about ammonia-oxidizing bacteria rather than LAB. (Read our interview with Mother Dirt to find out more.)
Lactobacillus bacteria, meanwhile, are being formulated into anhydrous serums (serums containing no water), and oil-and-water cosmetic creams .
Some cosmetic developers are using LAB strains isolated from skin, however, because probiotics used in foods are well known and easily sourced, the LAB species associated with probiotic types of cosmetics may not necessarily be the strains found in the skin microbiome.
References Jabr, F. (2017). ‘ Do Probiotics Really Work?’. Scientific American Vol. 317, Issue 1 10.1038/scientificamerican0717-26  Bull, M., Plummer, S., Marchesi, J., and Mahenthiralingam, E., (2013) ‘The life history of Lactobacillus acidophilus as a probiotic: a tale of revisionary taxonomy, misidentification and commercial success’, FEMS Microbiology Letters, Volume 349, Issue 2, Pages 77–87, https://doi.org/10.1111/1574-6968.12293  Long, G.Y., Wei Y.X., Tu, W., Gu C.T., (2020) ”Lactobacillus hegangensis sp. nov., Lactobacillus suibinensis sp. nov., Lactobacillus daqingensis sp. nov., Lactobacillus yichunensis sp. nov., Lactobacillus mulanensis sp. nov., Lactobacillus achengensis sp. nov., Lactobacillus mutagenesis sp. nov., Lactobacillus gannanensis sp. nov., Lactobacillus binensis sp. nov. and Lactobacillus angrenensis sp. nov., isolated from Chinese traditional pickle and yogurt” International Journal of Systematic and Evolutionary Microbiology. Volume 70, Issue 4 .
First Published: 26 February 2020 https://doi.org/10.1099/ijsem.0.004060 Bharadwaj, A.R., Singh, K.N., Wood, J.M., Debieu, M., O’Hara, N.B., Karouia, F., Mason, C.E., Venkateswaran, K., (2020) ”Draft Genome Sequences of Lactobacillales Isolated from the International Space Station”. Microbiology Resource Announcements Sep 2020, 9 (39) e00942-20.
DOI: 10.1128/MRA.00942-20 Martín R, Langa S, Reviriego C, Jimínez E, Marín ML, Xaus J, Fernández L, Rodríguez JM. Human milk is a source of lactic acid bacteria for the infant gut. J Pediatr. 2003 Dec;143(6):754-8. doi: 10.1016/j.jpeds.2003.09.028. PMID: 14657823. Pasolli, E., De Filippis, F., Mauriello, I.E. et al. Large-scale genome-wide analysis links lactic acid bacteria from food with the gut microbiome. Nat Commun 11, 2610 (2020). https://doi.org/10.1038/s41467-020-16438-8  Sfriso, R., Egert, M., Gempeler, M., Voegeli, R., and Campiche, R. (2019)
‘Revealing the secret life of skin ‐ with the microbiome you never walk alone.’
International Journal of Cosmetic Science. Volume42, Issue2. p116-126. https://doi.org/10.1111/ics.12594