An emerging zoonotic clone in the Netherlands provides clues to virulence and zoonotic potential of Streptococcus suis

Abstract

Streptococcus suis is a zoonotic swine pathogen and a major public health concern in Asia, where it emerged as an important cause of bacterial meningitis in adults. While associated with food-borne transmission in Asia, zoonotic S. suis infections are mainly occupational hazards elsewhere. To identify genomic differences that can explain zoonotic potential, we compared whole genomes of 98 S. suis isolates from human patients and pigs with invasive disease in the Netherlands, and validated our observations with 18 complete and publicly available sequences. Zoonotic isolates have smaller genomes than non-zoonotic isolates, but contain more virulence factors. We identified a zoonotic S. suis clone that diverged from a non-zoonotic clone by means of gene loss, a capsule switch, and acquisition of a two-component signalling system in the late 19th century, when foreign pig breeds were introduced. Our results indicate that zoonotic potential of S. suis results from gene loss, recombination and horizontal gene transfer events.

Distribution of Type I Restriction–Modification Systems in Streptococcus suis: An Outlook

“…To our knowledge, this is the only S. suis CC20 isolate reported from outside of the Netherlands [17]. With this finding, we corroborate a previously established ancestral link between the Dutch CC20 isolates and Chinese isolates [9]. …”

“…We sequenced 116 S. suis isolates from the Netherlands and performed a whole genome analysis to search for genetic factors important for zoonotic potential [9]. The single S. suis serotype causing zoonotic infection in the Netherlands is serotype 2, which belongs to either multi-locus sequence type (MLST) clonal complex (CC) 1 or CC20 [14].…”

“…In homology groups, which were created previously [9], the presence of a Type I R subunit was searched for. An hmmsearch for the Type I restriction enzyme R protein N terminus protein family (HSDR_N, PF04313.10) was performed using a randomly selected protein representative for each of the homology groups.…”

“…The bacterial isolates analyzed in this communication have previously been described [9,14]. Metadata for these isolates are attached in Supplementary Table S3.…”

“…The mechanisms responsible for switching from a carriage state to a virulent state are not well understood. Recently, we identified a novel Type I R–M system on a prophage in a zoonotic Streptococcus suis clone in the Netherlands [9]. Little is known about R–M systems in S. suis except for the Type II R–M system SsuDat1I which was described by Sekizaki et al [10,11,12].…”