Streptococcus suis: the Threat Remains

Abstract

Streptococcus suis is an important pathogen associated with a range of diseases in pigs, including meningitis, septicemia, pneumonia, endocarditis, and arthritis. The most important candidates for virulence factors in S. suis serotype 2 are the capsular polysaccharide (CPS) and the virulence related proteins, like muramidase-released protein (MRP), extracellular protein factor (EF), suilysin, and adhesins. The majority of S. suis strains produce narrow zones of alpha-hemolysis on sheep blood agar plates. Presumptive identification based on four biochemical tests (Voges-Proskauer, salicin, trehalose, and 6.5% NaCl) is possible for almost all capsular types of S. suis. Drug resistance to antibiotics varies in different countries. Tetracycline resistance has been observed in almost all S. suis strains isolated from all locations. Various types of vaccines for control of S. suis have been developed for pigs, with varied protective efficacy. The major vaccine commonly used in the pig industry, however, remains an inactivated autogenous vaccine generated from virulent strains from sick pigs. The most common gross lesions are congestion of the meninges, lymph nodes, and lungs, and the most common histopathological findings are within the choroidal plexus. A reference procedure to identify the S. suis serotype 2 issued by the Chinese CDC, which included staining, hemolytic analysis, serological clarification, biochemical analysis, and PCR assay, was used in diagnosis during the outbreaks of S. suis in China in 2005.