Probiotics are defined as "live micro-organisms that, when administered in adequate amounts, confer a health benefit to the host" (Hill et al, 2014). These microbes are generally applied in the gastrointestinal tract via fermented food products or capsules. In previous research, the investigators isolated bacterial strains with potential probiotic properties for the upper respiratory tract based on in vitro laboratory tests, in vivo mice experiments and genome sequencing.

In this study, the investigators want to deliver the Proof-of-Concept that the most promising isolated strain, Lactobacillus casei AMBR2 (LAMBR2) and the well-documented probiotic strain Lactobacillus rhamnosus GG (LGG) also have interesting properties in humans, i.e. that these strains are able to -temporarily- persist in the upper respiratory tract of healthy volunteers and CRS patients after daily nasal application via a nasal spray for 2 weeks. In addition, the investigators aim to explore whether the application of these strains has an impact on the nasopharyngeal microbiome via 16S rRNA amplicon sequencing and dedicated qPCR analysis.

Therefore, bacterial DNA from nasal swabs will be isolated via commercially available DNA extraction kits, followed by Illumina MiSeq sequencing in order to identify the bacterial species present in these samples. Furthermore, the concentration of the Lactobacillus and specific pathogens will be monitored via qPCR.

Inclusion Criteria:

• CRS patient group: CRS diagnosed

Exclusion Criteria:

• no patients with trisomy 21
• no pregnant women
• no breastfeeding women
• no acute or chronic airway infections (except for CRS patients in CRS patient group)
• no cancer
• no autoimmune diseases