Next-generation DNA sequencing analysis of two Streptococcus suis ST28 isolates associated with human infective endocarditis and meningitis in Gunma, Japan: a case report

Streptococcus suis (S. suis) is an important emerging zoonotic agent. Here, we report two cases of S. suis infection in pig farmers in Gunma Prefecture, Japan. We conducted a high-resolution molecular epidemiologic analysis on the basis of whole-genome sequencing data of each isolate using next-generation sequencing (NGS). NGS analysis revealed that the two S. suis clinical isolates were belonged to serotype 2 ST28. Phylogenetic analysis showed that two isolates were closely related to S. suis strains isolated from pigs in Japan at least until 1995. Since 41 nucleotide substitutions were found between the two strains, these strains might be derived from the same genetic lineage but distinct sporadic cases. NGS analysis is a powerful diagnostic tool for analysing bacterial infections. The database is more fulfilling, and more detailed analysis will become possible in the near future. Attention should be paid to S. suis infections, especially if the patient works on a livestock farm.