Pseudomonas aeruginosa Type IV pilus and resistance to the antimicrobial properties of surfactant protein-A
The lung contains numerous innate immune cells and effector proteins. One important component of this immune system is the surfactant protein-A (SP-A), which facilitates microbial clearance by opsonization and membrane permeabilization. Pseudomonas aeruginosa (PA) is a major Gram-negative bacterial pathogen commonly associated with chronic lung infection in cystic fibrosis. In order to resist the antibacterial effects of SP-A, PA expresses various structural and secreted virulence factors. Previously, Wu et al (2003) have shown that Escherichia coli lipopolysaccharides (LPS) are important in resisting SP-A-mediated membrane permeabilization. Zhang et al (2005) performed a comparative signature-tagged mutagenesis screen to identify PA virulence factors needed to resist SP-A-mediated lung clearance, and identified PchA (isochorismate synthase) and PtsP (phosphoenolpyruvate protein phosphotransferase) as important for resisting SP-A-mediated membrane permeability. Zhang et al (2007) further showed that PA flagellum is important for resisting SP-A-mediated membrane permeabilization. Finally, Kuang et al (2011) have shown PA elastase degrades SP-A, allowing an avenue for PA to escape SP-A-mediated opsonization and membrane permeabilization. In this study, we demonstrated that type IV pilus (Tfp) is important in the resistance of lung clearance both in the presence and absence of SP-A. The Tfp-deficient mutant, ΔpilA, is severely attenuated in an acute pneumonia model of infection in the lungs of wild-type mice that it allows similar bacterial load as PAO1 in the lungs of SP-A-/- mice. The ΔpilA bacteria are more susceptible to SP-A-mediated aggregation and opsonization. In addition, the integrity of the outer membranes of ΔpilA bacteria is compromised, rendering them more susceptible to SP-A-mediated membrane permeabilization. By using Tfp extension and retraction mutants, we demonstrate that the increased susceptibility of ΔpilA to SP-A-mediated opsonization is caused by the total absence of Tfp from PA cells. Finally, we provide evidence that increased expression of an 18 kDa nonpilus adhesin OprH in ΔpilA, may explain why there is an increased susceptibility to SP-A-mediated phagocytosis. In addition, we also have shown that Tfp glycosylation with O-antigen subunits allows for increased resistance to SP-A. We have also shown the glycosyltransferase mutant, 1244G7, which is deficient in O-antigen, is more susceptible to SP-A-mediated lung clearance and phagocytosis, but not membrane permeability. Finally, we have shown that the increase susceptibility of 1244G7 is associated with exposure of putative mannose residues.
Pseudomonas aeruginosa, Surfactant protein-A, Type IV pilus
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign