Commensal Bacteria in the Cystic Fibrosis Airway Microbiome Reduce P. aeruginosa Induced Inflammation

Abstract

Chronic Pseudomonas aeruginosa infections play an important role in the progress of lung disease in patients suffering from cystic fibrosis (CF). Recent studies indicate that polymicrobial microbiome profiles in the airway are associated with less inflammation. Thus, the hypothesis was raised that certain commensal bacteria might protect the host from inflammation. We therefore performed a screening study with commensals isolated from CF airway microbiome samples to identify potential beneficial commensals. We isolated more than 80 aerobic or facultative anaerobic commensal strains, including strains from genera Streptococcus, Neisseria, Actinomyces, Corynebacterium, Dermabacter, Micrococcus and Rothia. Through a screening experiment of co-infection in human epithelial cell lines, we identified multiple commensal strains, especially strains belonging to Streptococcus mitis, that reduced P. aeruginosa triggered inflammatory responses. The results were confirmed by co-infection experiments in ex-vivo precision cut lung slices (PCLS) from mice. The underlying mechanisms of the complex host-pathogen-commensal crosstalk were investigated from both the host and the bacterial sides with a focus on S. mitis. Transcriptome changes in the host in response to co-infection and mono-infection were evaluated, and the results indicated that several signalling pathways mediating inflammatory responses were downregulated by co-infection with S. mitis and P. aeruginosa compared to P. aeruginosa mono-infection, such as neutrophil extracellular trap formation. The genomic differences among S. mitis strains with and without protective effects were investigated by whole genome sequencing, revealing genes only present in the S. mitis strains showing protective effects. In summary, through both in vitro and ex vivo studies, we could identify a variety of commensal strains that may reduce host inflammatory responses induced by P. aeruginosa infection. These findings support the hypothesis that CF airway commensals may protect the host from inflammation.

Exploring the Cystic Fibrosis Lung Microbiome: Making the Most of a Sticky Situation

“…Co-infection models in human epithelial cell lines with P. aeruginosa and commensal CF microbiota have shown that different strains of Streptococcus mitis reduce P. aeruginosa -induced inflammation through reduction of interleukin 8 (IL-8) production and neutrophil extracellular trap (NET) formation. The mechanism of action is still unknown but thought to be through modification of the micro-environment by metabolism adjustment by the commensal bacteria [ 55 ]. In contrast, some oral commensal streptococci enhance P. aeruginosa pathogenicity by increasing its virulence factor expression (eg, pyocyanin and elastase) [ 4 , 56 , 57 ].…”

“…Although most studies to date have identified interactions that increase virulence of CF pathogens, it is expected that antagonistic interactions abound. Recently, in vitro data have demonstrated that several commensal isolates of Streptococcus mitis and Streptococcus oralis from sputum can reduce pro-inflammatory responses of patient-derived airway epithelial cells to P. aeruginosa [ 55 ]. Importantly, these findings were strain, not species, specific further highlighting the need for detailed profiling beyond 16S community level in the CF microbiome.…”

Inflammation and Infection in Cystic Fibrosis: Update for the Clinician

“…The presence of thick mucus and the vicious cycle of infection and inflammation has an impact on the lung microbiome in patients with CF [ 9 ]. The interaction between different bacteria in the lungs of patients with CF may be associated with the severity of inflammation in the lungs [ 9 ].…”

“…The presence of thick mucus and the vicious cycle of infection and inflammation has an impact on the lung microbiome in patients with CF [ 9 ]. The interaction between different bacteria in the lungs of patients with CF may be associated with the severity of inflammation in the lungs [ 9 ]. There are conflicting data on the role of different bacterial species, especially the role of facultative anaerobes of the usually so-called “oropharyngeal flora” in the lung of individuals with CF and if the interactions lead to more or less infection and inflammation [ 10 ].…”

“…Another recent study looked at the possible protective role of commensal strains (aerobic and anaerobic) toward less inflammation [ 9 ]. In this study using airway epithelial cells and the ex-vivo murine precision-cut lung slices murine lung model, it was shown that ex-vivo simultaneous infection of commensals, especially Streptococcus mitis with P. aeruginosa, was associated with reduced inflammatory response [ 9 ].…”