(Open access funding provided by Semmelweis University)
The SARS-CoV-2 virus is still causing a worldwide problem. The virus settles primarily
on the nasal mucosa, and the infection and its course depend on individual susceptibility.
Our aim was to investigate the nasopharynx composition’s role in the individual susceptibility.
During the first phase of SARS-CoV-2 pandemic, nasopharyngeal microbiome samples of
close contact unvaccinated patients were investigated by 16S rRNA analysis and by
culturing. The whole genome of cultured Corynebacteria was sequenced. The relative
expression of ACE2, TMPRSS2, and cathepsin L on Caco-2 cells and the strength of S1-ACE2
binding were determined in the presence of Corynebacteria . From 55 close contacts
exposed to identical SARS-CoV-2 exposure, 26 patients became infected and 29 remained
uninfected. The nasopharyngeal microbiome analysis showed significantly higher abundance
of Corynebacteria in uninfected group. Corynebacterium accolens could be cultivated
only from uninfected individuals and Corynebacterium propinquum from both infected
and uninfected. Corynebacteria from uninfected patient significantly reduced the ACE2
and cathepsin L expression. C. accolens significantly reduced the TMPRSS2 expression
compared to other Corynebacteria . Furthermore, Corynebacterium spp. weakened the
binding of the S1-ACE2. Most C. accolens isolates harbored the TAG lipase LipS1 gene.
Based on these results, the presence of Corynebacterium spp. in the nasopharyngeal
microbiota, especially C. accolens strains, could reduce the individual susceptibility
to SARS-CoV-2 infection by several mechanisms: by downregulation the ACE2, the TMPRSS2
receptors, and cathepsin L in the host; through the inhibition of S1-ACE2 binding;
and lipase production. These results suggest the use of C. accolens strains as probiotics
in the nasopharynx in the future.
