Contribution of Short Chain Fatty Acids to the Growth of Pseudomonas aeruginosa in Rhinosinusitis

Abstract

<b>Background:</b> Chronic rhinosinusitis (CRS) is characterized by complex bacterial infections with persistent inflammation. Based on our rabbit model of sinusitis, blockage of sinus ostia generated a shift in microbiota to a predominance of mucin degrading microbes (MDM) with acute inflammation at 2 weeks. This was followed by conversion to chronic sinus inflammation at 3 months with a robust increase in pathogenic bacteria (e.g., <i>Pseudomonas</i>). MDMs are known to produce acid metabolites [short chain fatty acids (SCFA)] that have the potential to stimulate pathogen growth by offering a carbon source to non-fermenting sinus pathogens (e.g., <i>Pseudomonas</i>). The objective of this study is to evaluate the concentrations of SCFA within the mucus and its contribution to the growth of <i>P. aeruginosa</i>. <b>Methods:</b> Healthy and sinusitis mucus from the rabbit model were collected and co-cultured with the PAO1 strain of <i>P. aeruginosa</i> for 72 h and colony forming units (CFUs) were determined with the targeted quantification of three SCFAs (acetate, propionate, butyrate). Quantification of SCFAs in healthy and sinusitis mucus from patients with <i>P. aeruginosa</i> was also performed via high performance liquid chromatography. <b>Results:</b> To provide evidence of fermentative activity, SCFAs were quantified within the mucus samples from rabbits with and without sinusitis. Acetate concentrations were significantly greater in sinusitis mucus compared to controls (4.13 ± 0.53 vs. 1.94 ± 0.44 mM, <i>p</i> < 0.01). After 72 h of co-culturing mucus samples with PAO1 in the presence of mucin medium, the blue-green pigment characteristic of <i>Pseudomonas</i> was observed throughout tubes containing sinusitis mucus. CFUs were higher in cultures containing mucus samples from sinusitis (8.4 × 10⁹ ± 4.8 × 10⁷) compared to control (1.4 × 10⁹ ± 2.0 × 10⁷) or no mucus (1.5 × 10⁹ ± 2.1 × 10⁷) (<i>p</i> < 0.0001). To provide evidence of fermentative activity in human CRS with <i>P. aeruginosa</i>, the presence of SCFAs in human mucus was analyzed and all SCFAs were significantly higher in CRS with <i>P. aeruginosa</i> compared to controls (<i>p</i> < 0.05). <b>Conclusion:</b> Given that SCFAs are solely derived from bacterial fermentation, our evidence suggests a critical role for mucin-degrading bacteria in generating carbon-source nutrients for pathogens. MDM may contribute to the development of recalcitrant CRS by degrading mucins, thus providing nutrients for potential pathogens like <i>P. aeruginosa</i>.