Thymidine starvation promotes c-di-AMP dependent inflammation during infection

Summary Antibiotics remain one of the most effective methods for controlling bacterial infection. However, the diverse impacts of antimicrobials on bacterial physiology and host immunity remain unclear. A comprehensive antibiotic screen revealed that disruption of thymidine synthesis in Firmicutes with anti-folate antibiotics promoted elevated levels of the bacterial second messenger cyclic di-AMP, and consequently induced host STING activation during infection. Extensive exposure to antibiotics targeting folate synthesis drives the emergence of thymidine-dependent Staphylococcus aureus SCVs (TD-SCVs). Respiratory infections with TD-SCVs are common among children with cystic fibrosis and are associated with worse clinical outcomes, although the underlying pathophysiological mechanisms remain to be defined. Our study reveals that TD-SCV isolates exhibited excessive c-di-AMP production and STING activation in a thymidine-dependent manner. Murine lung infection with TD-SCVs revealed STING-dependent elevation of proinflammatory cytokines, leading to higher airway neutrophil infiltration and activation comparing to normal colony S. aureus and hemin-dependent SCV. Our results suggest the elevated inflammatory capacity of TD-SCVs contribute to their pathogenesis and revealed a new aspect of STING signaling in the airway by characterizing its role in neutrophil recruitment.