USE OF POLYMYXIN B IN A CAPTURE ENZYME IMMUNOASSAY FOR DETECTION OF SALMONELLAE SPP. LIPOPOLYSACCHARIDE

A capture enzyme immunoassay for detection of salmonellae sp. lipopolysaccharide was developed. The assay made use of polymyxin B sulfate, passively attached to a polystyrene matrix, to capture lipopolysaccharide. Bound lipopolysaccharride was then detected with a monoclonal antibody, specific for salmonellae spp. followed by goat antimouse antibody conjugated with horseradish peroxidase.
The analytical sensitivity of the assay was approximately 1 ng/ml of lipopolysaccharide. The results are comparable to those obtained with a competitive enzyme immunoassay previously developed. The sensitivity of the polymyxin B assay decreased to 4–5 ng/ml when the salmonellae spp. lipopolysaccharide was mixed with 1–100 μg/ml of Escherichia coli lipopolysaccharide, while this level of heterogeneous lipopolysaccharide, did not decrease the sensitivity of the competitive enzyme immunoassay.
The polymyxin B capture assay was advantageous in that polymyxin B is a standardized reagent that is relatively inexpensive and does not require extensive preparation or containment facilities. The assay is robust; however, because of the light sensitivity of polymyxin B, its stickiness to other reagents and interference by other lipopolysaccharides, this assay requires careful attention to detail and may therefore be an unsuitable assay for field use.