LSC Abstract – Severity of lung tissue pathology is dictated by S. aureus toxins eliciting series of cytolytic and chemotactic responses

S. aureusis a major cause of hospital and community acquired pneumonia. Several virulence factors such as α-toxin, PVL and cytolytic peptides are implicated as major mediators of tissue pathology. Here we use a novel organotypic model of human lung to address the role of exotoxins produced by clinical S. aureus strains causing varying severity of lung infection i.e necrotizing pneumonia(NP) and lung empyema(LE). Exposure of lung tissue models to bacterial supernatants revealed that the NP strains were highly cytotoxic, demonstrating accentuated inflammation, necrosis and loss of Ecadherin, whereas the LE strain induced limited tissue damage. This corresponded to higher levels of α-toxin and PVL being produced by the NP strains, as compared to the LE strain that produced moderate levels of PVL but no α-toxin. A direct role of α-toxin in epithelial disruption was verified by toxin deficient mutants and pure α-toxin. PVL contributed to epithelial injury indirectly through lysis of neutrophils. Notably combined effects of α-toxin and PVL further augmented the tissue pathology. The study identifies a novel immunomodulatory effect of these toxins resulting in strong upregulation and polarization of CXCL8 and CX3CL1 chemokines towards the apical side of the epithelium translating into increased chemotaxis. Association between toxin levels, cytotoxicity and clinical outcome was confirmed in a larger cohort of pneumonia isolates. This study provides novel insight into toxin-mediated roles in lung tissue pathology implicating both α-toxin and PVL in chemotactic and cytolytic events contributing to severe tissue injury linked to NP.