Role of Inflammasome-Mediated Pyroptosis as a Mechanism of Pathogenicity in Pseudomonas Biofilms

Author(s): Keerthi S, Vishnu Raj M, and Maya Nandkumar A

Most of the studied mechanisms of pathogenesis hold true for planktonic bacterial infections, while pathogenesis of biofilm is less well understood. Hence, in the current study, we delineate the mechanism of pathogenicity of Pseudomonas biofilms. The model systems used to understand cell-microbial interactions were A549 monolayers representing lung epithelium, THP1 cells representing the immune system, and a combination of both, representing a multicellular system. Our study shows that biofilm of Pseudomonas on endotracheal tube (ETT) reduced reactive oxygen species generation in A549 and THP1. Assessment of morphological changes during infection revealed features of both apoptosis and necrosis in all systems challenged with biofilms of Pseudomonas. Biofilm infection in A549, THP1, and their co-cultures showed increased expression of tumour necrosis factor α (TNFα) but decreased interleukin 8 (IL8) and IL6 expression and induced nitric oxide synthase (iNOS) expression. A reduction in IL8, IL6 and iNOS was observed in all the three model systems challenged with Pseudomonas biofilms on ETT, with a concomitant observation of DNA fragmentation, within an intact nuclear membrane. Taken together, our data suggest that biofilms induce inflammasome activation, as evidenced by the increase in casapase 1 and IL-1β upregulation; downregulation of caspase 3 rules out apoptosis as a mechanism of pathogenicity. This provides an insight into the mechanism of chronic inflammation during biofilm infection.