Pseudomonas aeruginosaP. aeruginosa P. aeruginosaP. aeruginosaP. aeruginosa.The present invention provides synthetic lipooligosaccharide (LOS) based oligosaccharides and conjugates containing various serotype specific oligosaccharide antigens or various core oligosaccharide structures or motifs. The invention further provides LOS based immunogenic and immunoprotective compositions and antibodies derived therefrom for diagnosing treating and preventing infections caused by