AUTHOR=Aradanas Maverick , Poljak Zvonimir , Fittipaldi Nahuel , Ricker Nicole , Farzan Abdolvahab 

TITLE=Serotypes, Virulence-Associated Factors, and Antimicrobial Resistance of Streptococcus suis Isolates Recovered From Sick and Healthy Pigs Determined by Whole-Genome Sequencing

JOURNAL=Frontiers in Veterinary Science

VOLUME=8

YEAR=2021

URL=https://www.frontiersin.org/journals/veterinary-science/articles/10.3389/fvets.2021.742345

DOI=10.3389/fvets.2021.742345

ISSN=2297-1769

ABSTRACT=<p><italic>Streptococcus suis</italic> is ubiquitous in swine, and yet, only a small percentage of pigs become clinically ill. The objective of this study was to describe the distribution of serotypes, virulence-associated factor (VAF), and antimicrobial resistance (AMR) genes in <italic>S. suis</italic> isolates recovered from systemic (blood, meninges, spleen, and lymph node) and non-systemic (tonsil, nasal cavities, ileum, and rectum) sites of sick and healthy pigs using whole-genome sequencing. In total, 273 <italic>S. suis</italic> isolates recovered from 112 pigs (47 isolates from systemic and 136 from non-systemic sites of 65 sick pigs; 90 isolates from non-systemic sites of 47 healthy pigs) on 17 Ontario farms were subjected to whole-genome sequencing. Using <italic>in silico</italic> typing, 21 serotypes were identified with serotypes 9 (13.9%) and 2 (8.4%) as the most frequent serotypes, whereas 53 (19.4%) isolates remained untypable. The relative frequency of VAF genes in isolates from systemic (Kruskal–Wallis, <italic>p</italic> &lt; 0.001) and non-systemic (Kruskal–Wallis, <italic>p</italic> &lt; 0.001) sites in sick pigs was higher compared with isolates from non-systemic sites in healthy pigs. Although many VAF genes were abundant in all isolates, three genes, including <italic>dltA</italic> [Fisher's test (FT), <italic>p</italic> &lt; 0.001], <italic>luxS</italic> (FT, <italic>p</italic> = 0.01), and <italic>troA</italic> (FT, <italic>p</italic> = 0.02), were more prevalent in isolates recovered from systemic sites compared with non-systemic sites of pigs. Among the isolates, 98% had at least one AMR gene, and 79% had genes associated with at least four drug classes. The most frequently detected AMR genes were <italic>tetO</italic> conferring resistance to tetracycline and <italic>ermB</italic> conferring resistance to macrolide, lincosamide, and streptogramin. The wide distribution of VAFs genes in <italic>S. suis</italic> isolates in this study suggests that other host and environmental factors may contribute to <italic>S. suis</italic> disease development.</p>