Acidic and alkaline conditions enhance Staphylococcus aureus α-toxin pore formation and cytotoxicity

Staphylococcus aureus α-toxin (AT) is a potent pore-forming toxin that causes cell damage during infection. The structure and activity of AT have been studied extensively, but the environmental factors that modulate its toxicity remain unclear. Here, we demonstrate that the extracellular pH modulates AT cytotoxicity through two independent mechanisms in human cells. First, we show that acidic conditions enhance AT pore maturation, causing a toxin-intrinsic and ADAM10 independent increase in cytotoxicity after prolonged exposure to AT. Second, we demonstrate that both acidic and alkaline conditions impair the cellular capacity to internalize AT pores, resulting in toxin retention at the cell surface and increased cytotoxicity after pulse intoxication. The cell-intrinsic, pH-dependent sensitization to AT is observed in various human cell types but not for other pore forming toxins. Together, our findings indicate that the extracellular pH modulates AT activity and host cell susceptibility.