Investigation and genome-wide analysis of Streptococcus suis in large-scale pig farms

Swine streptococcosis is a zoonotic disease caused by infection with Streptococcus suis, which has occurred globally multiple times and seriously threatens pig farming and public health. With the expansion of pig farming and the ban on antibiotics, the problem of antibiotic resistance in Streptococcus suis has intensified, with the emergence of multi-drug resistant strains and difficulty in treatment. However, there have been few reports on the antibiotic resistance status, virulence factor carrying situation, and diversity changes of Streptococcus suis in the main pig farming areas during the breeding process. Therefore, this study conducted a survey and whole-genome analysis of Streptococcus suis in 8 main pig farming areas from 2022 to 2023. A total of 766 samples were collected, and 158 strains of Streptococcus suis were isolated, revealing severe antibiotic resistance. The results of whole-genome sequencing (WGS) detected 9 classes of 32 antibiotic resistance genes, 15.2% of the strains had virulence factors (EPF, SLY, MRP), and some had high pathogenicity. Importantly, this study discovered 13 novel antibiotic resistance genes that had not been described in Streptococcus suis before, including aac(6')-Im, ant(4')-Ia, aph(2'')-Iia, blaROB-1, cat-TC, catA16, catA7, catA8, lnu(C), msr(D), tet(