Role of the Tet38 Efflux Pump in Staphylococcus aureus Internalization and Survival in Epithelial Cells

Abstract

ABSTRACT We previously identified the protein Tet38 as a chromosomally encoded efflux pump of Staphylococcus aureus that confers resistance to tetracycline and certain unsaturated fatty acids. Tet38 also contributes to mouse skin colonization. In this study, we discovered a novel regulator of tet38 , named tetracycline regulator 21 (TetR21), that bound specifically to the tet38 promoter and repressed pump expression. A Δ tetR21 mutant showed a 5-fold increase in tet38 transcripts and an 8-fold increase in resistance to tetracycline and fatty acids. The global regulator MgrA bound to the tetR21 promoter and indirectly repressed the expression of tet38 . To further assess the full role of Tet38 in S. aureus adaptability, we tested its effect on host cell invasion using A549 (lung) and HMEC-1 (heart) cell lines. We used S. aureus RN6390, its Δ tet38 , Δ tetR21 , and Δ mgrA mutants, and a Δ tet38 ΔtetR21 double mutant. After 2 h of contact, the Δ tet38 mutant was internalized in 6-fold-lower numbers than RN6390 in A549 and HMEC-1 cells, and the Δ tetR21 mutant was internalized in 2-fold-higher numbers than RN6390. A slight increase of 1.5-fold in internalization was found for the Δ mgrA mutant. The growth patterns of RN6390 and the Δ mgrA and Δ tetR21 mutants within A549 cells were similar, while no growth was observed for the Δ tet38 mutant. These data indicate that the Tet38 efflux pump is regulated by TetR21 and contributes to the ability of S. aureus to internalize and replicate within epithelial cells.