Prevalence of O1/K1-and O2/K3-reactive Actinobacillus suis in healthy and diseased swine

A cell surface antigen-typing system was devised for the swine pathogen Act inobacillus suis and used to examine the prevalence of different lipopolysa ccharide (O) types in healthy and diseased pigs. The strains examined in th is study mere isolated from a variety of locations in Canada and from Kansa s. Lipopolysaccharide preparations of 151 isolates of A. suis were characte rized by immunoblotting using polyclonal antisera generated to strains SO-I (O1/K1), H89-1173 (O2/K3), and VSB 3714, a rough strain, Approximately 54% (62 of 114) of A. suis isolates from diseased pigs, all (11 of 11) isolate s from healthy pigs, and all (4 of 4) reference strains reacted with O1/K1 antiserum. More than 80% (18 of 22) of A. suis strains used for bacterin pr oduction and approximately 41% (47 of 114) of isolates from diseased pigs b ound O2/K3 antiserum, One isolate appeared to be rough, and five were untyp eable. O1/K1- and O2/K3-reactive strains were equally prevalent in Kansas, whereas O2/K3-reactive strains were more common in Quebec and western Canad a and O1/K1 strains were most common in Ontario, The fact that virtually al l of the strains submitted for bacterin production mere O2/K3-reactive stra ins is consistent,vith the notion that these strains may be more virulent t han O1/K1 strains; alternatively, this may reflect geographic or other bias es. In addition, we observed cross-reactivity between A. suis cell surface antigens and swine antisera to several other important pathogens. This find ing may explain why previous attempts to develop a simple serodiagnostic te st for A. suis have been unsuccessful.