['We have previously demonstrated that persistent symptoms following functional endoscopic sinus surgery for chronic rhinosinusitis (CRS) is associated with Gram-negative bacterial carriage. Mechanisms for this remain unknown. We wished to determine whether Gram-negative carriage in patients with CRS with nasal polyposis is associated with a more severe inflammatory phenomenon.', 'Three hundred and thirty-seven patients with CRS with nasal polyposis (CRSwNP) previously phenotyped for genetic association studies with questionnaire, serum biomarkers, and endoscopically-obtained swab cultures were studied. These were separated according to the presence (wGN) or absence (sGN) of Gram-negative bacterial carriage; demographic parameters and available serum biomarkers (complete blood count [CBC], total immunoglobulin E [IgE]) were then compared. Subgroup analysis for Pseudomonas aeruginosa (GNwPa) and non-Pseudomonas Gram-negative bacteria (GNsPs) was performed in order to explore potentially differential roles of these bacteria.', 'Gram-negative bacterial carriage was not associated with a difference in demographic parameters or serum biomarkers. However, P. aeruginosa carriage was associated with a higher self-reported incidence of asthma (GNwPa 79%, sGN 57%; p = 0.048). Interestingly, serum IgE was increased in the non-Pseudomonas Gram-negative population (GNsPs: 338 IU/mL, sGN: 195 IU/mL; p = 0.026).'] Is gram-negative bacterial carriage in chronic rhinosinusitis with nasal polyposis associated with more severe inflammation?