MUTANTS OF STREPTOCOCCUS-SUIS TYPE-1 AND TYPE-2 IMPAIRED IN EXPRESSION OF MURAMIDASE-RELEASED PROTEIN AND EXTRACELLULAR PROTEIN INDUCE DISEASE IN NEWBORN GERM-FREE PIGS

The contribution of muramidase-released protein (MRP) and extracellula r factor (EF) to the virulence of Streptococcus suis type 1 and 2 infe ctions was studied. For that aim, we constructed mutants of S. suis ty pes 1 and 2 by inactivating the genes encoding MRP and EF, Moreover, w e changed a type 2 strain producing the 110-kDa EF protein into a stra in producing a modified protein (EF) of increased molecular mass, The chromosomally located mrp and epf genes were inactivated by replaceme nt recombination by using nonreplicative plasmids. Newborn germfree pi gs were inoculated with pathogenic type 1 and 2 strains and with the i sogenic mutant strains. Wild-type as well as mutant strains induced fe ver, specific signs of disease, and lesions. Moreover, all mutant stra ins could be reisolated from the central nervous system of infected pi gs. These results showed that inactivation or alteration of the mrp an d epf genes had no measurable effect on the pathogenicity of S. suis t ypes 1 and 2.