Pf Bacteriophage and Their Impact on Pseudomonas Virulence, Mammalian Immunity, and Chronic Infections

Pf bacteriophage are temperate phages that infect the bacterium Pseudomonas aeruginosa, a major cause of chronic lung infections in cystic fibrosis (CF) and other settings. Pf and other temperate phages have evolved complex, mutualistic relationships with their bacterial hosts that impact both bacterial phenotypes and chronic infection. We and others have reported that Pf phages are a virulence factor that promote the pathogenesis of P. aeruginosa infections in animal models and are associated with worse skin and lung infections in humans. Here we review the biology of Pf phage and what is known about its contributions to pathogenesis and clinical disease. First, we review the structure, genetics, and epidemiology of Pf phage. Next, we address the diverse and surprising ways that Pf phages contribute to P. aeruginosa phenotypes including effects on biofilm formation, antibiotic resistance, and motility. Then, we cover data indicating that Pf phages suppress mammalian immunity at sites of bacterial infection. Finally, we discuss recent literature implicating Pf in chronic P. aeruginosa infections in CF and other settings. Together, these reports suggest that Pf bacteriophage have direct effects on P. aeruginosa infections and that temperate phages are an exciting frontier in microbiology, immunology, and human health.

Filamentous bacteriophages are associated with chronic Pseudomonas lung infections and antibiotic resistance in cystic fibrosis

Filamentous bacteriophage (Pf phage) contribute to the virulence of Pseudomonas aeruginosa infections in animal models, but their relevance to human disease is unclear. We sought to interrogate the prevalence and clinical relevance of Pf phage in patients with cystic fibrosis (CF) using sputum samples from two well-characterized patient cohorts. Bacterial genomic analysis in a Danish longitudinal cohort of 34 patients with CF revealed that 26.5% (n = 9) were consistently Pf phage positive. In the second cohort, a prospective cross-sectional cohort of 58 patients with CF at Stanford, sputum qPCR analysis showed that 36.2% (n = 21) of patients were Pf phage positive. In both cohorts, patients positive for Pf phage were older, and in the Stanford CF cohort, patients positive for Pf phage were more likely to have chronic P. aeruginosa infection and had greater declines in pulmonary function during exacerbations than patients negative for Pf phage presence in the sputum. Last, P. aeruginosa strains carrying Pf phage exhibited increased resistance to antipseudomonal antibiotics. Mechanistically, in vitro analysis showed that Pf phage sequesters these same antibiotics, suggesting that this mechanism may thereby contribute to the selection of antibiotic resistance over time. These data provide evidence that Pf phage may contribute to clinical outcomes in P. aeruginosa infection in CF.

Phospholipase C activation during elicitation of the oxidative burst in cultured plant cells

Although phospholipase C hydrolysis of polyphosphoinositides constitutes one of the major second messenger pathways in animal cells, its participation in signal transduction in higher plants has not been established. To determine whether activation of phosphatidylinositol-directed phospholipase C might be involved in signaling the elicitor-induced oxidative burst in plants, suspension-cultured soybean cells were treated with two stimulants of the H2O2 burst and examined for polyphosphoinositide turnover. Both polygalacturonic acid elicitor and the G protein activator, mastoparan, promoted a transient increase in inositol 1,4,5-trisphosphate (IP3) content that exceeded basal IP3 levels (0.9 +/- 0.4 pmol of IP3/10(6) cells, n = 28) by 2.6- and 7-fold, respectively. In each case, intracellular IP3 content reached a maximum at 1 min post-stimulation and declined to near basal levels during the subsequent 5-10 min. Neomycin sulfate, an inhibitor of polyphosphoinositide hydrolysis, blocked the IP3 transient, and Mas-17, an inactive analogue of mastoparan, induced no change in IP3. Thin layer chromatography of lipid extracts of the soybean cells corroborated the above results by revealing a rapid decrease in phosphatidyl-inositol monophosphate and phosphatidylinositol 4,5-bisphosphate following polygalacturonic acid elicitor and mastoparan (but not Mas-17) stimulation. Since the rise in IP3 preceded H2O2 production and since neomycin sulfate inhibited the appearance of both, we hypothesize that phospholipase C activation might constitute one pathway by which elicitors trigger the soybean oxidative burst.