Bacteria in our nose

References to lactobacilli may make you think of yogurt (rich in these bacteria) or the intestinal microbiota, but did you know that these rod-shaped microorganisms which produce lactic acid (hence the name) are also present in our nasal passages?

Lactobacilli are more abundant in the nose in the absence of sinusitis

A comparison of the microbiota in the upper respiratory tract of around 100 healthy individuals with that of over 200 patients with chronic rhinosinusitis has shown lactobacilli to be more abundant in the nasal cavities (nose and nasopharynx) of the former group than in those of the latter. By observing lactobacilli (sidenote: Lactobacilli Rod-shaped bacteria whose main characteristic is the production of lactic acid, from where they get the name “lactic acid bacteria”.  Lactobacilli are present in the oral, vaginal and gut microbiota of humans, but also in plants and animals. They are found in fermented foods, such as dairy products (e.g. certain cheeses and yoghurts), pickles, sauerkraut, etc. Lactobacilli are also found in probiotics, with certain species recognized for their beneficial properties.   W. H. Holzapfel et B. J. Wood, The Genera of Lactic Acid Bacteria, 2, Springer-Verlag, 1st ed. 1995 (2012), 411 p. « The genus Lactobacillus par W. P. Hammes, R. F. Vogel Tannock GW. A special fondness for lactobacilli. Appl Environ Microbiol. 2004 Jun;70(6):3189-94. Smith TJ, Rigassio-Radler D, Denmark R, et al. Effect of Lactobacillus rhamnosus LGG® and Bifidobacterium animalis ssp. lactis BB-12® on health-related quality of life in college students affected by upper respiratory infections. Br J Nutr. 2013 Jun;109(11):1999-2007. ) more closely in “healthy noses”, the researchers noted certain features that make them especially suited to the upper airways. These included their ability to live in an oxygen-rich environment (i.e. the nose)–instead of one containing no oxygen, such as the bottom of a yogurt–thanks to the acquisition of tools enabling them to survive therein.

When colonization is only a few hairs away

In particular, certain types of Lactobacillus casei (a species of lactobacillus) identified in healthy noses displayed multiple hairs allowing them to adhere strongly to the nasal walls. Like Spider-Man scaling a building, these specific lactobacilli can climb our nasal cavities even against wind (sneezing) and rain (runny noses). Once in place, L. casei inhibits infectious agents by preventing them from settling in the ground it has already occupied and hindering their growth via the lactic acid it produces.

A probiotic spray soon?

These initial results led the researchers to test a spray containing these “hairy lactobacilli” in 20 healthy volunteers. The results revealed that the bacteria seem able to settle, at least temporarily, in the nasal cavities. Therefore, the beneficial role of lactobacilli is far from being limited to the intestinal and vaginal microbiota. Their effect on the respiratory tract, hitherto largely unknown, gives hope for new approaches in the treatment of chronic respiratory diseases.