Streptococcus suis occasionally causes invasive diseases in pigs, but the main source of infection remains still unclear. To understand the dynamics of S. suis in pig farms, we compared the distribution of S. suis in pig farms and the swine oral microbiota between Japan and Vietnam.
Clinically healthy pigs, enrolled from each of two farms in two countries, were categorized by their growth stages as follows: suckling, post-weaning, growing and their sows. Samples were collected from their bodies (saliva, feces, vagina swabs) and surroundings (swabs of water dispenser and feed box). Relative numbers of total bacteria, S. suis of all serotypes, and S. suis serotype 2, which is predominantly isolated from diseased pigs, were estimated by Real-time PCR. The swine oral microbiota was investigated by high-throughput sequencing of 16S rRNA gene.
S. suis were detected from all saliva. Relative numbers of S. suis in the saliva were the same order irrespective of the growth stages, farms, or nations, while the other samples showed lower detection rate and numbers of S. suis than those of saliva. S. suis serotype 2 was detected in the samples from a few farms where S. suis infection occurred frequently. The oral microbiota seemed to be more similar among the growth stages than between two countries. These results suggested that swine saliva could be a potential reservoir of S. suis regardless of the growth stages; however, the oral microbiota would be affected by the growth stages rather than geographical and/or environmental differences between two countries.