Sulfide Protects Staphylococcus aureus from Aminoglycoside Antibiotics but Cannot Be Regarded as a General Defense Mechanism against Antibiotics

Sulfide production has been proposed to be a universal defense mechanism against antibiotics in bacteria (K. Shatalin, E. Shatalina, A. Mironov, and E. Nudler, Science 334:986–990, 2011, doi:10.1126/science.1209855). To gain insight into the mechanism underlying sulfide protection, we systematically and comparatively addressed the interference of sulfide with antibiotic activity against Staphylococcus aureus, as a model organism. The impact of sulfide and sulfide precursors on the antibiotic susceptibility of S. aureus to the most important classes of antibiotics was analyzed using modified disk diffusion assays, killing kinetic assays, and drug uptake studies. In addition, sulfide production and the impact of exogenously added sulfide on the physiology of S. aureus were analyzed. Sulfide protection was found to be limited to aminoglycoside antibiotics, which are known to be taken up by bacterial cells in an energy-dependent process. The protective mechanism was found to rely on an inhibitory effect of sulfide on the bacterial respiratory chain, leading to reduced drug uptake. S. aureus was found to be incapable of producing substantial amounts of sulfide. We propose that bacterial sulfide production should not be regarded as a general defense mechanism against antibiotics, since (i) it is limited to aminoglycosides and (ii) production levels vary considerably among species and, as for S. aureus, may be too low for protection.