NtrBC Selectively Regulates Host-Pathogen Interactions, Virulence, and Ciprofloxacin Susceptibility of Pseudomonas aeruginosa

Abstract

Pseudomonas aeruginosa is a metabolically versatile opportunistic pathogen capable of infecting distinct niches of the human body, including skin wounds and the lungs of cystic fibrosis patients. Eradication of P. aeruginosa infection is becoming increasingly difficult due to the numerous resistance mechanisms it employs. Adaptive resistance is characterized by a transient state of decreased susceptibility to antibiotic therapy that is distinct from acquired or intrinsic resistance, can be triggered by various environmental stimuli and reverted by removal of the stimulus. Further, adaptive resistance is intrinsically linked to lifestyles such as swarming motility and biofilm formation, both of which are important in infections and lead to multi-drug adaptive resistance. Here, we demonstrated that NtrBC, the master of nitrogen control, had a selective role in host colonization and a substantial role in determining intrinsic resistance to ciprofloxacin. P. aeruginosa mutant strains (ΔntrB, ΔntrC and ΔntrBC) colonized the skin but not the respiratory tract of mice as well as WT and, unlike WT, could be reduced or eradicated from the skin by ciprofloxacin. We hypothesized that nutrient availability contributed to these phenomena and found that susceptibility to ciprofloxacin was impacted by nitrogen source in laboratory media. P. aeruginosa ΔntrB, ΔntrC and ΔntrBC also exhibited distinct host interactions, including modestly increased cytotoxicity toward human bronchial epithelial cells, reduced virulence factor production and 10-fold increased uptake by macrophages. These data might explain why NtrBC mutants were less adept at colonizing the upper respiratory tract of mice. Thus, NtrBC represents a link between nitrogen metabolism, adaptation and virulence of the pathogen P. aeruginosa, and could represent a target for eradication of recalcitrant infections in situ.

Competition between Pseudomonas aeruginosa and Staphylococcus aureus is dependent on intercellular signaling and regulated by the NtrBC two-component system

“…7 ). We confirmed previous observations for PA14 mutant strains 16 , in showing that virulence factor production was significantly downregulated in strain LESB58 Δ ntrBC and/or Δ ntrC strains (Fig. 7 A–C), depending on the virulence factor.…”

“…Genes in the NtrC regulon 14 , 15 are involved in surface colonization (e.g., muc operon), virulence in acute and chronic infections (e.g., algU , pvdD , pscH , phuR ) and scavenging of nutrients (e.g., nap , nas , nir operons), some of which have no annotated σ 54 binding site. Accordingly, we previously demonstrated 15 , 16 that NtrBC regulated several adaptive lifestyles of P. aeruginosa including biofilm formation in vitro, colonization in a subcutaneous infection model in vivo and expression of virulence factors.…”

Pseudomonas aeruginosa two-component system LadS/PA0034 regulates macrophage phagocytosis via fimbrial protein cupA1

“…Macrophage uptake assay was performed as previously with slight changes ( 49 ). Briefly, murine macrophage-like RAW264.7 cells were cultured in RPMI-1640 medium supplemented with 10% fetal bovine serum at 37°C in a 5% CO 2 environment.…”

The many antibiotic resistance and tolerance strategies of Pseudomonas aeruginosa

“…While the molecular mechanisms of resistance are not fully understood, this phenotype is primarily driven by environmental stimuli such as antimicrobial exposure, pH changes, anaerobic environments, and starvation. Adaptive resistance has also been highly linked to swarming motility, biofilm development, and a transient upregulation of the MexXY-OprM efflux pump [ [47] , [48] , [49] ]. Once the antibiotic pressure is removed, the adaptive resistance bacteria are able to revert to a wild-type level of antibiotic susceptibility [ 48 ].…”