AVIRULENCE AND IMMUNOGENICITY IN MICE OF A BOVINE MASTITIS STAPHYLOCOCCUS-AUREUS MUTANT

An avirulent mutant, designated RC122, was derived from Staphylococcus aureus bovine mastitis strain RC108 after N-methyl-N'-nitro-N-nitroso guanidine mutagenesis, Mutant RC122, which was isolated on the basis o f reduced colony size, showed diminished virulence in mice (LD50 of RC 122: 3.1 x 10(10) cfu vs LD50 of RC108: 2.3 x 10(7) cfu), Mutant RC122 grew more slowly than its parental strain and showed decreased produc tion of several exoproteins, such as alpha- and beta-hemolysin, DNAse and coagulase, The production of its capsule was induced only under in vivo growth conditions. Clearance studies performed in the mouse kidn ey revealed that the kinetics of disappearance of the mutant was simil ar to that of its parental strain. Protection experiments carried out by intraperitoneal administration in mice showed that mutant RC122 con ferred a good degree of protection from challenge with homologous and heterologous strains.