Whole-genome sequencing of samples from a Streptococcus parasuis infection

Streptococcus parasuis (S. parasuis) is a close relative of Streptococcus suis (S. suis), and they cause similar clinical symptoms. This retrospective study aimed to identify clinical phenotypic and genetic characteristics of a S. parasuis (namely isolate S1) isolated twice in succession from pleural effusion of an elderly patient with atypical manifestations and to further conduct a systematic literature overview for prevention and control of human S. parasuis infection. The isolate S1 was initially identified as Enterococcus raffinosus (95.5% confidence) by VITEK^®2COMPACT, and subsequently confirmed as S. suis by MALDI-TOF-MS (99.9% confidence). Average nucleotide identity value of isolate S1 (CP137602) showed a sequence similarity of 97.9% to S. parasuis (GCF_004283785), and 16 S rRNA gene sequence confirmed a similarity of 99.86% to S. parasuis (GenBank: No. 069079). The isolate S1 harboring 1,700 COG-annotated genes contained 1,538 predicted functional genes in six different classifications. Except for a potential virulence-associated gene responsible for production of hyaluronic acid capsule, no antimicrobial resistance gene was disclosed. The isolate S1 harboring toxin gene hasC owned an anti-phagocytosis potential, and it was susceptible to antimicrobials tested (9/10), with only intermediate susceptible to Clindamycin. Till December 2024, only 3 articles covering 4 cases of human S. parasuis infection have been reported. This is the first S. parasuis isolate from pleural effusion in a patient with atypical manifestations. Literature overview and our subsequent successful identification of its clinical phenotypic and genetic characteristics have greatly raised the awareness of potential opportunistic Zoonotic S. parasuis infection in humans, which may serve as a reference for medical professionals.