Flagellum-Mediated Biofilm Defense Mechanisms of Pseudomonas aeruginosa against Host-Derived Lactoferrin

Abstract

Chronic infection with the gram-negative organism Pseudomonas aeruginosa is a leading cause of morbidity and mortality in human patients, despite high doses of antibiotics used to treat the various diseases this organism causes. These infections are chronic because P. aeruginosa readily forms biofilms, which are inherently resistant to antibiotics as well as the host's immune system. Our laboratory has been investigating specific mutations in P. aeruginosa that regulate biofilm bacterial susceptibility to the host. To continue our investigation of the role of genetics in bacterial biofilm host resistance, we examined P. aeruginosa biofilms that lack the flgK gene. This mutant lacks flagella, which results in defects in early biofilm development (up to 36 h). For these experiments, the flgK-disrupted strain and the parental strain (PA14) were used in a modified version of the 96-well plate microtiter assay. Biofilms were challenged with freshly isolated human leukocytes for 4 to 6 h and viable bacteria enumerated by CFU. Subsequent to the challenge, both mononuclear cells (monocytes and lymphocytes) and neutrophils, along with tumor necrosis factor alpha (TNF-␣), were required for optimal killing of the flgK biofilm bacteria. We identified a cytokine cross talk network between mononuclear cells and neutrophils that was essential to the production of lactoferrin and bacterial killing. Our data suggest that TNF-␣ is secreted from mononuclear cells, causing neutrophil activation, resulting in the secretion of bactericidal concentrations of lactoferrin. These results extend previous studies of the importance of lactoferrin in the innate immune defense against bacterial biofilms.

Human Tear Fluid Reduces Culturability of Contact Lens-Associated Pseudomonas aeruginosa Biofilms but Induces Expression of the Virulence-Associated Type III Secretion System

“…Biofilms are communities of surface-associated microbial cells in a heterogenous protective matrix of polysaccharides, proteins, and nucleic acids. 8–10 Biofilm growth can enhance bacterial tolerance to antimicrobial agents 11–13 and to host immune responses, 14–16 and involves changes in microbial metabolism, gene expression, and contributions from the matrix itself. 17 P. aeruginosa biofilms readily form on human contact lenses and in lens storage cases.…”

Biofilm formation and serum susceptibility in Pseudomonas aeruginosa

“…In addition, its ability to form biofilm provides greater protection against host immune defense systems and susceptibility to various antimicrobial agents [16,17]. P. aeruginosa is a multidrug resistant (MDR) organism and is considered a phenomenon of bacterial resistance.…”

Interactions between Neutrophils and Pseudomonas aeruginosa in Cystic Fibrosis

“…NE degrades bacterial flagellin and represses its transcription [209,210]. Lactoferrin, a PMN antibacterial product, attacks flagellin-dependent biofilm formation of P. aeruginosa [211]. Extrusion of NETs induced by motile P. aeruginosa must primarily occur in early disease stages characterized by flagellated bacterial forms (Figure 1).…”