Abstract: The present invention relates to a broadly reactive vaccine against Gram-negative bacteria which is composed of a biological glycan-pilus conjugate. The conjugate core is a common pilus type to which is attached the glycan of choice in vivo. Pooling of these bioconjugates produces a multivalent vaccine. These pili give high bronchial titers when delivered by the intranasal route. Mice vaccinated with pure glycosylated P. aeruginosa strain 1244 pili in this manner are protected against respiratory challenge with P. aeruginosa strain 1244. The present invention further relates to a DNA and amino acid sequence of a new gene, pilO, which is capable of glycosylating pilin of Gram-negative bacteria and uses thereof.