Lactic acid bacteria as probiotics for the nose?

Abstract

Several studies have recently pointed towards an increased occurrence and prevalence of several taxa of the lactic acid bacteria (LAB) in the microbiota of the upper respiratory tract (URT) under healthy conditions versus disease. These include several species of the Lactobacillales such as Lacticaseibacillus casei, Lactococcus lactis and Dolosigranulum pigrum. In addition to physiological studies on their potential beneficial functions and their long history of safe use as probiotics in other human body sites, LAB are thus increasingly to be explored as alternative or complementary treatment for URT diseases. This review highlights the importance of lactic acid bacteria in the respiratory tract and their potential as topical probiotics for this body site. We focus on the potential probiotic properties and adaptation factors that are needed for a bacterial strain to optimally exert its beneficial activity in the respiratory tract. Furthermore, we discuss a range of in silico, in vitro and in vivo models needed to obtain better insights into the efficacy and adaptation factors specifically for URT probiotics. Such knowledge will facilitate optimal strain selection in order to conduct rigorous clinical studies with the most suitable probiotic strains. Despite convincing evidence from microbiome association and in vitro studies, the clinical evidence for oral or topical probiotics for common URT diseases such as chronic rhinosinusitis (CRS) needs further substantiation.

Fig. 1

Mean relative abundances of Dolosigranulum (red bars) and Lactobacillaceae (blue bars) as part of the microbiome in different human body habitats. Based on our research (De Boeck et al., 2019,2020) and available literature (Laufer et al., 2011; Biesbroek et al., 2014a; Stearns et al., 2015; Hasegawa et al., 2017; Gan et al., 2020), Dolosigranulum and Lactobacillus are proposed as indicator taxa for health. Using the curatedMetagenomicData R‐package based on publicly available shotgun sequencing data data (Pasolli et al., 2017), their mean relative abundances were calculated in the URT, skin, gut and vagina. N.d., not detected.

Fig. 2

Probiotic and adaptation factors in the URT compared with the gastrointestinal tract. Probiotic factors related to antipathogenic effects, immunomodulation and barrier protection are more conserved across different human body sites, while each body site has its own unique features that determine the adaptation factors that are needed for a probiotic to be effective in that body site. Figure adapted from (Lebeer et al., 2008; Man et al., 2017) and created with BioRender.com 121 × 64 mm (300 × 300 DPI)