The first description of a (1 -> 6)-beta-D-glucan in prokaryotes: (1 -> 6)-beta-D-glucan is a common component of Actinobacillus suis and is the basis for a serotyping system

The chemical and antigenic properties of the cell-surface lipopolysaccharid es (LPSs) and capsular polysaccharides (CPSs) of seven representative strai ns of Actinobacillus suis from healthy and diseased pigs were investigated. Four strains produced a linear (1 --> 6)-beta-D-glucan homopolymer, beta-D -Glcp-(1-[ --> 6)-beta-D-Glcp-(1-](n) -->, as a LPS-O-chain (O1) and as a C PS (K1). Polyclonal antisera prepared against a (1 --> 6)-beta-D-glucan-con taining strain showed a positive reaction against both LPSs and CPSs derive d from the above strains (designated serotype O1/K1). One strain carried th e (1 --> 6)-beta-D-glucan solely as a LPS-O-chain (serotype O1) and two str ains did not express the (1 --> 6)-beta-D-glucan, but, instead, produced a different O-chain (designated serotype O2); these three strains expressed t heir own characteristic CPSs. (1 --> 6)-beta-D-Glucan structures are common cell wall components of yeast, fungi and lichens, but, to our knowledge, t his is the first time a (1 --> 6)-beta-D-glucan has been described in a pro karyotic organism. Conformational and nuclear magnetic resonance analyses s howed that the beta-D-Glcp-(1 --> 6)-beta-D-Glcp linkage was flexible and t wo distinct glycosidic conformers are described. Cross-reactive antibodies to the A. suis (1 --> 6)-beta-D-glucan could be detected in sera from a var iety of species and in sera from specific pathogen free pigs. This cross-re activity may arise from immune-stimulation of organisms present in the surr ounding environment that contain (1 --> 6)-beta-D-glucan, which may also ex plain the high incidence of false positive results in previous serological tests for A. suis. In addition, these (1 --> 6)-beta-D-glucan background an tibodies may be protective against A. suis infection. The characterization herein of (1 --> 6)-beta-D-glucan is the foundation for the development of a serotyping system for A. suis. (C) 2000 Elsevier Science Ltd. All rights reserved.