Serotypes, main virulence genes, and multilocus sequence typing of 199 clinical isolates of Streptococcus suis

Abstract:

[Background] Streptococcus suis (SS) has a variety of serotypes, genotypes, and virulence factors. [Objective] To reveal the serotypes, virulence gene distribution, molecular typing characteristics and their associations of SS clinical isolates. [Methods] A total of 199 clinical isolates of SS were collected in this study. We employed PCR to detect the serotypes and virulence genes and carried out multilocus sequence typing (MLST). Further, we analyzed the prevalence and associations of serotypes, virulence genotypes and sequence types (STs). [Results] The 199 SS clinical isolates belonged to 16 serotypes (1, 2, 3, 4, 6, 7, 8, 9, 10, 12, 15, 16, 21, 24, 29, and 30). The serotypes 2, 4, and 3 were dominant, respectively involving 26.13% (52/199), 14.57% (29/199), and 12.06% (24/199) of the strains, and 21.61% (43/199) of the strains were untypable. We identified 72 STs, among which ST1, ST94, ST117, ST7, ST28, and ST87 were dominant, the strains of which accounted for 12.56% (25/199), 11.56% (23/199), 9.56% (19/199), 9.04% (18/199), 6.03% (12/199), and 3.01% (6/199), respectively. Twenty-four STs (ST1224-ST1227, ST1229-ST1235, ST1241−ST1242, and ST1300-ST1310) were newly discovered. In addition, these 72 STs involved 12 cloning complexes and 32 single STs. The detection rate of the virulence gene fbps in the 199 isolates was 96.98% (193/199). A total of 19 virulence genotypes were detected, among which epf‒/mrp‒/sly‒/gapdh+/fbps+/orf2+ were dominant (66 strains, 33.17%). [Conclusion] In recent years the serotypes 2, 4, and 3 were dominant among the clinical isolates of SS. ST had obvious genetic heterogeneity and high degree of intraspecific differentiation. The serotypes and STs showed certain crossover. The isolates in this study presented varied distribution of virulence genes and diverse virulence genotypes. In this study, the epidemiological characteristics of SS clinical isolates were investigated to provide scientific basis for diagnosis, treatment and prevention and control measures of SS disease.

Key words:Streptococcus suis;serotype;virulence gene;multilocus sequence typing (MLST)