Historically antibody has been associated with improved host clearance of bacteria, although within the last decade a novel subset of antibody was found to inhibit complement-mediated killing in patients with chronic Gram-negative infections. This “inhibitory” antibody was found to be IgG2 specific to O-antigen, and was correlated with impaired disease in P. aeruginosa-infected patients with bronchiectasis [1]. As such, a novel salvage therapy for untreatable P. aeruginosa infections in two patients with bronchiectasis was conducted, known as plasmapheresis. This treatment involved total removal of antibody resulting in greatly improved patient disease symptomology and outcomes [2]. However this therapy is imprecise requiring removal of potentially protective antibody, highlighting the need for refinement of this therapy to produce a column that selectively removes inhibitory antibody. In addressing this, lipopolysaccharide from P. aeruginosa was purified using hot-phenol water extraction, where O-polysaccharide was separated from the lipid-A:core component via acetic-acid hydrolysis. O-antigen from varying serotypes (O3, O5, O6 and O11) was biotinylated at the Kdo residue of the terminal polysaccharide, and affixed to 1 mL streptavidin-sepharose columns. Chronically infected patient serum was applied to the column, and subsequent flowthrough and eluted antibody was tested for the ability to inhibit serum killing of cognate bacterial isolates in vitro. O-antigen columns were able to separate antigen-specific polyclonal antibody from sera across all tested serotypes showing no-detectable signs of O-antigen-specific antibody in flowthrough. In turn, normal serum killing was restored in patient serum depleted of O-antigen specific antibody and conversely, O-antigen-specific antibody in saline at physiological titres inhibited serum killing from cognate P. aeruginosa serotypes (P < 0.05). These results reinforce the mechanism of inhibitory antibody in complement-mediated killing and also provide a medium to purify O-antigen specific antibody targeting a range of O-serotypes. More promisingly, this technique of antibody purification also provides a preliminary means to develop novel therapies that involve removal of inhibitory antibodies from chronically-ill patients.