The invention provides for an isolated antibody that specifically recognizes a galactan-III epitope of the lipopolysaccharide (LPS) O-antigen structure of Klebsiella pneumoniae, which epitope is incorporated in galactan-III repeating units, wherein the galactan-III repeating unit is a branched galactose homopolymer of Formula (I). The invention further provides for a pharmaceutical or diagnostic preparation comprising said antibody, and a method of producing said antibody.