Pseudomonas aeruginosa (PA) leads to chronic respiratory infections especially in patients with cystic fibrosis patients and chronic obstructive pulmonary disease (COPD), characterized by a high morbidity. After screening Lactobacilli coming from CF expectorations, on their capacity to inhibit two Pseudomonas aeruginosa (PA) virulence factors (elastase, pyocyanin), the inventors evaluated the effect of intranasal administration of Lactobacilli on PA murine pneumonia. The primary outcome was the bacterial lung load 24 hours after PA induced pneumonia. To understand the role of Lactobacillus, the chemokines, the pro and anti-inflammatory BAL rates were also measured. The administration of Lactobacilli cocktail 18 h prior the PA lung infection decreases significantly the lung bacterial load at 24 h post-infection. Although the mechanisms need to be deeply explored, an immunomodulation effect may be involved, notably through the recruitment of neutrophils. Thus the present relates to a method of treating a Pseudomonas aeruginosa respiratory tract infection in a patient in need thereof comprising administering to the patient's respiratory tract a therapeutically effective amount of at least one Lactobacillus strain.