Genetic analysis of Streptococcus suis isolates recovered from diseased and healthy carrier pigs at different stages of production on a pig farm

Streptococcus suis isolates from pigs at different stages of production on a farrow-to-finish farm were characterised by serotyping, pulsed-field gel electrophoresis (PFGE) and production of muramidase-released protein, extracellular factor and suilysin. S. suis was isolated from the tonsils of 81/287 (28.2%) healthy pigs: 16/47 (34%) post-weaning, 18/47 (38.3%) transition, 18/47 (38.3%) fattening and 29/146 (19.9%) sows. A total of 127 S. suis isolates were analysed: 14 from diseased pigs at the post-weaning stage and 113 from the tonsils of healthy pigs. Serotypes 2, 4, 9, 14 and 1/14 were isolated from both diseased and healthy pigs. A total of 83 PFGE profiles were obtained; most isolates (95.2%) were grouped into three clusters (A–C). Animals at different production stages harboured isolates with similar phenotypic and genetic profiles, highlighting the importance of healthy animals in the maintenance of strains responsible for outbreaks of clinical disease.