Comparison of Cell Surface Antigen Extracts From Two Serotypes of Pasteurella haemolytica

1 Moredun Research Institute, 408 Gilmerton Road, Edinburgh EH 17 7JH, UK 2 Department of Bacteriology, University of Edinburgh Medical School, Teviot Place, Edinburgh EH8 9AG, UK ABSTRACT Cells of Pasteurella haemolytica serotypes Al and A6 were extracted with sodium salicylate and the chemical and antigenic composition of both extracts determined. The extracts were concentrated by ultrafiltration and the serotype antigen, measured by the indirect haemagglu-tination test, was estimated to have a molecular weight between 100000 and 300000. The chemical composition of sodium salicylate extracts (SSEs) from both serotypes was similar, having protein, carbohydrate, fatty acid and phosphorus present in the ratio 10:1:0-5:0-1. SDS-PAGE of both SSEs gave similar profiles with at least 48 bands present. These results suggest that sodium salicylate removes the outer membrane of P. haemolytica. Crossed immunoelectrophoresis indicated that a major serotype-specific antigen was present in SSEs of both strains. This antigen was extracted from the SSE with hot phenol/water and analysed by gas chromatography. The sugar composition of Al and A6 phenol/water extract (PWE) was qualitatively identical although some differences in proportions were observed. Al and A6 PWE antigens protected mice against homologous serotype challenge and A6 PWE protected against heterologous (Al) challenge.