The Pseudomonas aeruginosa flagellum confers resistance to pulmonary surfactant protein‐A by impacting the production of exoproteases through quorum‐sensing

Abstract

SummarySurfactant protein-A (SP-A) is an important antimicrobial protein that opsonizes and permeabilizes membranes of microbial pathogens in mammalian lungs. Previously, we have shown that Pseudomonas aeruginosa flagellum-deficient mutants are preferentially cleared in the lungs of wild-type mice by SP-Amediated membrane permeabilization, and not by opsonization. In this study, we report a flagellummediated mechanism of P. aeruginosa resistance to SP-A. We discovered that flagellum-deficient (DfliC) bacteria are unable to produce adequate amounts of exoproteases to degrade SP-A in vitro and in vivo, leading to its preferential clearance in the lungs of SP-A +/+ mice. In addition, DfliC bacteria failed to degrade another important lung antimicrobial protein lysozyme. Detailed analyses showed that DfliC bacteria are unable to upregulate the transcription of lasI and rhlI genes, impairing the production of homoserine lactones necessary for quorum-sensing, an important virulence process that regulates the production of multiple exoproteases. Thus, reduced ability of DfliC bacteria to quorum-sense attenuates production of exoproteases and limits degradation of SP-A, thereby conferring susceptibility to this major pulmonary host defence protein.

Pseudomonas aeruginosa Elastase Provides an Escape from Phagocytosis by Degrading the Pulmonary Surfactant Protein-A

“…Also, there are reports of elastase inactivating secretory immunoglobulin A, immunoglobulin G and opsonin C3 [31], [48]–[50]. Most recently, we have confirmed that P. aeruginosa LasB is able to degrade lysozyme in vitro [22], [51].…”

“…Also, SP-A activates phagocytic cells and upregulates the expression of host cell-surface receptors involved in microbial recognition [8], [17]–[21]. Most recently, we and others have reported that SP-A also directly kills microbes in a macrophage-independent manner by increasing the permeability of microbial membranes [22]–[27]. However, the mechanism by which SP-A permeabilizes microbial membranes and its relative importance in the lung defense is not clear.…”

Type IV Pilus Glycosylation Mediates Resistance of Pseudomonas aeruginosa to Opsonic Activities of the Pulmonary Surfactant Protein A

“…4B). Prolonged exposure abolished the difference of phagocytic efficiency between 1244 and ⌬tfpO strains, most probably due to the production of exoproteases that degraded SP-A, as we had previously reported (28,32). These observations were confirmed by in vivo phagocytosis assays, which showed that ⌬tfpO bacteria were 4.5-fold more susceptible to SP-A-mediated phagocytosis than was strain 1244 (Fig.…”

“…As discussed above, SP-A mediates its antimicrobial effects by enhancing microbial clearance through membrane permeabilization and opsonization (22,24,(28)(29)(30)(31)(32). To further examine whether O-glycosylation of P. aeruginosa Tfp with O-ag increases the resistance to SP-A-mediated membrane permeability, we measured the amounts of leaked thiol containing proteins from 1244 versus ⌬tfpO mutant after exposure to hSP-A.…”

“…We have previously shown that flagellum, another prominent appendage of P. aeruginosa, is important for resistance to SP-A-mediated opsonization and membrane permeabilization (32,37). Similar to Tfp, the flagella of P. aeruginosa can be classified into two groups (a-type and b-type) based on the posttranslational O-glycosylation of flagellins with deoxyhexose (23,(38)(39)(40)(41)(42)(43)(44).…”