Correlation of T2R38 taste phenotype and in vitro biofilm formation from nonpolypoid chronic rhinosinusitis patients

Abstract

Background: Sinonasal biofilms have been demonstrated in specimens collected from chronic rhinosinusitis (CRS) patients. Mounting evidence suggests that biofilms contribute to therapeutically recalcitrant CRS. Recently, the bitter taste receptor T2R38 has been implicated in the regulation of the sinonasal mucosal innate immune response. TAS2R38 gene polymorphisms affect receptor functionality and contribute to variations seen in sinonasal innate defense as well as taste perception reflected in gustatory sensitivity to the bitter compound phenylthiocarbamide (PTC). In a population of CRS patients with active infection or inflammation, we sought to determine if a correlation between T2R38 phenotype and in vitro biofilm formation existed.

Methods: Endoscopically guided sinonasal swabs were obtained prospectively from CRS (±polyp) patients with evidence of persistent inflammation or mucopurulence. In vitro biofilm formation was assessed with a modified Calgary Biofilm Detection Assay. Patients' phenotypic (functional) expression of the bitter taste receptor T2R38 was evaluated with a taste test including the compound PTC. Linear regression was used to determine the level of significance between mean in vitro biofilm formation levels and mean PTC taste test intensity ratings across CRS patients.

Results: Sinonasal swabs were obtained from 59 patients, with 42 of the 59 samples demonstrating in vitro biofilm formation. Analysis revealed an inverse linear association between in vitro biofilm formation and PTC taste intensity ratings (p = 0.019) for all patients. This association was exclusively driven by nonpolypoid CRS patients (p = 0.0026).

Conclusion: In vitro biofilm formation from sinonasal clinical isolates is inversely correlated with PTC taste sensitivity in nonpolypoid CRS patients.

Keywords: Calgary biofilm detection; Pseudomonas aeruginosa; T2R38 polymorphism; biofilm; bitter taste receptor; chronic rhinosinusitis; genetics; nitric oxide; phenylthiocarbamide; supertaster.

Figure 1

In vitro biofilm assay from consecutive endoscopically guided sinonasal cultures. Patients evaluated in the outpatient clinic who were found to have sinonasal mucopurulence or mucosal inflammation were cultured in duplicate. While 1 sample was analyzed by the hospital microbiology laboratory for culture and sensitivity, the duplicate swab was processed for detection of biofilm-forming capacity. Concomitant positive and negative controls were performed with the pseudomonal species PAO-1 (wt), Sad-31, and Sad-36. Severe biofilm formation is categorized by OD₅₉₅ greater than PAO-1 (wt), moderate OD₅₉₅ less than wt but greater than Sad-31. OD₅₉₅ = optical density measured at 595 nm; PAO1 = Pseudomonas aeruginosa; wt = wild-type.

Figure 2

PTC taste sensitivity correlates with TAS2R38 genotype. ANOVA testing on taste test scores yielded significant variation in PTC taste sensitivity among genotype groups, F(3, 36) = 74.59, p < 0.0001. A post hoc Tukey test yielded that PAV/PAV group and the AVI/AVI group differed significantly (mean difference = 9.55; 95% CI, 7.35 to 11.74) at p < 0.001; the PAV/AVI group and PAV/PAV group differed significantly (mean difference = 3.68; 95% CI, 1.62 to 5.73) at p < 0.001; and the PAV/AVI group and AVI/AVI group differed significantly (mean difference = 5.87; 95% CI, 4.20 to 7.54) at p < 0.001. ANOVA = analysis of variance; AVI = alanine-valine-isoleucine; CI = confidence interval; PCT = phenylthiocarbamide; PAV = proline-alanine-valine.

Figure 3

In vitro biofilm formation correlates to PTC taste sensitivity in CRS patients. (A) Biofilm formation was assessed (OD₅₉₅) on 59 clinical isolates from CRS patients and compared to their PTC taste sensitivity. A significant correlation was observed (p = 0.019, r² = 0.093). (B, C) Subjects were stratified based on the endoscopic presence of nasal polyps. In non-polyp patients (B) a significant correlation was observed (p = 0.0026, r² = 0.214) while in the polyp patients (C) no significant correlation was observed (p = 0.971, r² = 0.001). CRS = chronic rhinosinusitis; OD₅₉₅ = optical density measured at 595 nm; PCT = phenylthiocarbamide.

Figure 4

PTC taste score predicts in vitro biofilm formation in nonpolyp CRS patients. In vitro biofilm formation was assessed (OD₅₉₅) and compared to TAS2R38 genotype and PTC score for nonpolyp CRS patients, with 25 of those patients having been genotyped. PTC score was broadly divided into 2 categories, score 0 to 6 (n = 13) and score 7 to 12 (n = 12). (A) Patients with a PTC score of 7 to 12 had a significantly lower level of in vitro biofilm formation (p = 0.012, 2-tailed t test). (B) Comparison of TAS2R38 genotype with in vitro biofilm formation did not reach significance (1-way ANOVA, p = 0.204). ANOVA = analysis of variance; CRS = chronic rhinosinusitis; OD₅₉₅ = optical density measured at 595 nm; PCT = phenylthiocarbamide.