Identification of an African bacillus anthracis lineage that lacks expression of the spore surface associated anthrose containing oligosaccharide

The surface of Bacillus anthracis endospores exposes a pentasaccharide containing the monosaccharide anthrose which has been considered as vaccine or target for specific detection of the spores. In this study B. anthracis strains isolated from cattle carcasses in African countries where anthrax is endemic were tested for their cross-reactivity with monoclonal antibodies (mAbs) specific for anthrose containing oligosaccharides. Unexpectedly, none of the isolates collected in Chad, Cameroon and Mali were recognized by the mAbs. Sequencing of the four-gene operon, encoding anthrose biosynthetic enzymes, revealed the presence of premature stop codons in the amino-transferase and the glycosyltransferase genes in all isolates from Chad, Cameroon and Mali. Both immunological and genetic findings suggest that the West African isolates are unable to produce anthrose. The anthrose deficient strains from West Africa belong to a particular genetic lineage. Immunization of cattle in Chad with a locally produced vaccine based on anthrose-positive spores of the B. anthracis strain Sterne elicited an anti-carbohydrate IgG response specific for a synthetic anthrose containing tetrasaccharide as demonstrated by glycan microarray analysis. Competition immunoblots with synthetic pentasaccharide derivatives suggested an immunodominant role of the anthrose containing carbohydrate in cattle. In West Africa anthrax is highly endemic. Massive vaccination of livestock in this area has taken place over long periods of time using spores of the anthrose positive vaccine strain Sterne. Spread of anthrose deficient strains in this region may represent an escape strategy of B. anthracis