The Secretary of State in Her Britannic Majesty's Government of the

Richard J Manchee

Andrew Robinson

Derek C Ellwood

An antigenically-active cell envelope fraction from bacterial cells, especially Bordetella pertussis, may be isolated by disrupting the cells, separating the cell envelopes from the other cell components, extracting the separated envelopes with a solution of a zwitterionic surfactant and precipitating the cell envelope preparation from the resulting extract by the addition of a lower alkyl (C.sub.1 to C.sub.5) alcohol, preferably ethanol. The preferred extractant is an N, N, N-trialkyl zwitterionic compound especially an N, N, N-trialkyl-.alpha.-amino acid or an N, N, N-trialkyl amine oxide. The cell envelope fraction obtained from B. pertussis is highly protective against whole bacteria when tested by standard vaccine mouse potency assay and has a greatly reduced lipopolysaccharide content compared with either whole cells or crude cell envelopes, greatly reducing the risk of undesirable side-effects from vaccination.

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Salisbury, United Kingdom

Richard J Manchee