RT Journal Article SR Electronic(1) A1 Charland, Nathalie A1 Harel, Josée A1 Kobisch, Marylène A1 Lacasse, Serge A1 Gottschalk, MarceloYR 1998 T1 Streptococcus suis serotype 2 mutants deficient in capsular expression JF Microbiology, VO 144 IS 2 SP 325 OP 332 DO https://doi.org/10.1099/00221287-144-2-325 PB Microbiology Society, SN 1465-2080, AB Streptococcus suis serotype 2 is responsible for a wide variety of porcine infections. In addition, it is considered a zoonotic agent. Knowledge about the virulence factors for this bacterium is limited but its polysaccharide capsule is thought to be one of the most important. Transposon mutagenesis with the self-conjugative transposon Tn916 was used to obtain acapsular mutants from the virulent S. suis type 2 reference strain S735. Clones were screened by colony-dot ELISA with a monoclonal antibody specific for a type 2 capsular epitope and clones that failed to react with the antibody were characterized. Two mutants, 2A and 79, having one and two Tn916 insertions respectively, were chosen for further characterization. Absence of capsule was confirmed by coagglutination, capillary precipitation and capsular reaction tests and by transmission electron microscopy. Absence of capsular polysaccharides correlated with increased hydrophobicity and phagocytosis by both murine macrophages and porcine monocytes compared to the wild-type strain. Furthermore, both mutants were shown to be avirulent in murine and pig models of infection. Finally, mutant 2A was readily eliminated from circulation in mice compared to the wild-type strain, which persisted more than 48 h in blood. Thus, isogenic mutants defective in capsule production demonstrate the importance of capsular polysaccharides as a virulence factor for S. suis type 2., UL https://www.microbiologyresearch.org/content/journal/micro/10.1099/00221287-144-2-325