PHENOTYPIC CHARACTERIZATION AND VIRULENCE OF A SAE- AGR- MUTANT OF STAPHYLOCOCCUS-AUREUS

A sae::Tn551 agr::tetM double mutant was constructed and characterized . The production of several exoproteins (e.g., beta-hemolysin, DNase, and proteases) by this mutant was determined and found to be lower tha n the already diminished production of either isogenic single mutant s ae(-) or agr(-). The double mutant also showed, like the agr(-) mutant , null production of alpha- and delta-hemolysins and diminished levels of lipase. The reduced levels of many exoproteins in the double mutan t as compared with their already diminished levels in either single mu tant suggest that there is an additive or synergistic interaction betw een the two mutations involved, sae(-) and agr(-). However, inactivati on of both loci, sae and agi, had a different effect on the two exopro teins that are up regulated in the agr(-) mutant; thus, coagulase drop ped to levels close to the null levels of the sae(-) parental strain, while extracellular protein A displayed the high levels characteristic of the agr(-) single mutant. The virulence of the sae(-) agr(-) doubl e mutant, determined by intraperitoneal injection in mice, was found t o be significantly diminished as compared with that of the sae(+) agr( +) parental strain or the sae(-) agr(+) single mutant.