Pseudomonas aeruginosa is an opportunistic bacterium that mainly infects those who have previously been treated with antibiotics. We hypothesised that antibiotic treatment disrupts tryptophan metabolism, leading to increased susceptibility to P. aeruginosa infection. Our results showed that mice receiving antibiotics exhibited intestinal dysbiosis with alterations in host tryptophan metabolism, a higher mortality rate and a higher bacterial load compared to eubiotic mice. In the lungs of the dysbiotic mice, there was an increase in IDO1 (Indoleamine 2,3-dioxygenase 1) activity and an accumulation of kynurenine after infection, and IDO1