Isolation of Stable Hemolysin and Catalase Variants of Staphylococcus aureus S6C Includes One with an Exoprotein-Deficient Phenotype

Previous studies suggested that the exoprotein-deficient phenotype of a Δ1058::Tn551 insertion/deletion mutant of Staphylococcus aureus S6C was not owing to the insertion/deletion event, but instead was owing to the inherent instability of the agrC gene during transduction of the Δ1058::Tn551 region into S6C. The purpose of the following study was to examine S6C as a potential source of exoprotein-deficient mutants that would account for their appearance after transposition and transduction. Four stable variants of S6C were isolated that differed in their hemolysin and catalase activities. Surprisingly, the agr regulatory molecule, RNAIII, was undetectable in one of these variants, which most likely accounted for the exoprotein-deficient phenotype of this variant. When the original Δ1058::Tn551 mutation was transduced into the hemolytic, catalase-positive variant of S6C, none of the transductants exhibited an exoprotein-deficient phenotype. These data suggest that, while the exoprotein-deficient phenotype of the S6C variant is most likely due to mutations in the agr regulatory system, these mutations are not caused by the transduction of the Δ1058::Tn551 region into S6C, but instead already exist in an exoprotein-deficient variant of S6C. Received: 6 November 2000 / Accepted: 16 January 2001