[Distributions of pathogenic capsular types and in vitro antimicrobial susceptibility of different serotypes of Streptococcus suis isolated from clinically healthy sows from 10 provinces in China].

OBJECTIVE: To determine the distributions of major pathogenic capsular types and in vitro antimicrobial susceptibility of different serotypes of Streptococcus suis isolated from clinically healthy sows in China. METHODS: Tonsil specimens of clinically healthy sows from 10 different provinces in China were collected, a total of 421 S. suis were isolated. Capsular types of S. suis were decided using the sera agglutination reaction. Antimicrobial susceptibility testing was performed using a broth microdilution method and the differences between serotypes were decided statistically. RESULTS: The prevalent capsular types of S. suis isolated from clinically healthy sows were 9 (26.6%), 3 (23.5%) and 7 (15.7%) types, respectively. 7.4% of isolates were confirmed to be S. suis type 2. Overall, differences in antimicrobial susceptibility among serotypes of S. suis were found. By comparison, lower resistance was observed for S. suis type 2 from clinically healthy sows. CONCLUSION: The prevalence of pathogenic S. suis serotypes from clinically healthy sows again indicates S. suis is a conditional pathogenic bacterium. Differential prevention and treatment regimes should be considered according to antimicrobial susceptibility of different serotypes of S. suis.

Molecular mutations associated with the in vitro passage of virulent porcine reproductive and respiratory syndrome virus.

Mutants of a highly pathogenic, porcine reproductive, and respiratory syndrome virus (PRRSV), JXA1 strain, were prepared by continuous in vitro passage. Genomic sequence comparisons were made between mutants obtained at different passages and the parental strain JXA1. The mutant strain obtained at passage 80 contained a 12 nucleotide insertion and 108 nucleotide mutations that resulted in 45 amino acid changes. Most of these changes (89%) occurred between passage 10 and 45 and were genetically stable for the next 35-70 passages. A comparison of the mutants, their parental strain, and several American PRRSV strains, identified 13 characteristic amino acid changes. These sites, as well as the distinct 12 nucleotide insertion, represent possible genetic markers for the evaluation of live vaccine applications, particularly for additional studies of the safety and potency of live PRRSV vaccines.