Interactions between effector proteins of the Pseudomonas aeruginosa type III secretion system do not significantly affect several measures of disease severity in mammals

Shaver, Ciara M.; Hauser, Alan R.

doi:10.1099/mic.0.28368-0

Cited by 16 publications

(19 citation statements)

References 66 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…4). This is consistent with reports indicating that cosecretion of ExoS or ExoT along with ExoU did not substantially alter the severity of pneumonia (36). Nonetheless, cosecretion of other effector proteins could have subtle effects on the total numbers and proportions of host cells injected with ExoU.…”

Section: Discussionsupporting

confidence: 81%

Pseudomonas aeruginosa Cytotoxin ExoU Is Injected into Phagocytic Cells during Acute Pneumonia

Diaz¹,

Hauser

2010

Infect Immun

Self Cite

108

View full text Add to dashboard Cite

ExoU, a cytotoxin translocated into host cells via the type III secretion system of Pseudomonas aeruginosa, is associated with increased mortality and disease severity. We previously showed that impairment of recruited phagocytic cells allowed survival of ExoU-secreting P. aeruginosa in the lung. Here we analyzed types of cells injected with ExoU in vivo using translational fusions of ExoU with a ␤-lactamase reporter (ExoU-Bla). Cells injected with ExoU-Bla were detectable in vitro but not in vivo, presumably due to the rapid cytotoxicity induced by the toxin. Therefore, we used a noncytotoxic ExoU variant, designated ExoU(S142A)-Bla, to analyze injection in vivo. We determined that phagocytic cells in the lung were frequently injected with ExoU(S142A). Early during infection, resident macrophages constituted the majority of cells into which ExoU was injected, but neutrophils and monocytes became the predominant types of cells into which ExoU was injected upon recruitment into the lung. We observed a modest preference for injection into neutrophils over injection into other cell types, but in general the repertoire of injected immune cells reflected the relative abundance of these cells in the lung. Our results indicate that phagocytic cells in the lung are injected with ExoU and support the hypothesis that ExoU-mediated impairment of phagocytes has a role in the pathogenesis of pneumonia caused by P. aeruginosa.

show abstract

Section: Discussionsupporting

confidence: 81%

Pseudomonas aeruginosa Cytotoxin ExoU Is Injected into Phagocytic Cells during Acute Pneumonia

Diaz¹,

Hauser

2010

Infect Immun

Self Cite

108

View full text Add to dashboard Cite

show abstract

“…During acute P. aeruginosa infections, bacterial burden is not the only issue worth consideration. P. aeruginosa strains possessing or not possessing a T3SS colonize the lung to the same extent; however, expression of T3SS effectors facilitates systemic dissemination (49). Neutralization of innate immunity as well as systemic dissemination appears to be promoted by the activities of the P. aeruginosa effectors secreted by the T3SS.…”

Section: Discussionmentioning

confidence: 99%

Activation of ExoU Phospholipase Activity Requires Specific C-Terminal Regions

2010

View full text Add to dashboard Cite

Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen that utilizes a type III secretion system to subvert host innate immunity. Of the 4 known effector proteins injected into eukaryotic cells, ExoS and ExoU are cytotoxic. The cytotoxic phenotype of ExoU depends on the enzymatic activity of the patatin-like phospholipase A 2 domain localized to the N-terminal half of the protein. Amino acid residues located within the C-terminal region of ExoU are postulated to be required for trafficking or localization to the plasma membrane of eukaryotic cells. This report describes the characterization of a transposon-based linker insertion library in ExoU. Utilizing an unbiased screening approach and sensitive methods for measuring enzymatic activity, we identified regions of ExoU that are critical for activation of the phospholipase activity by the only known cofactor, SOD1. Insertions at D572 and L618 reduced the rate of substrate cleavage. Enzymatic activity could be restored to almost parental levels when SOD1 concentrations were increased, suggesting that the linker insertion disrupted the interaction between ExoU and SOD1. An enzyme-linked immunosorbent assay (ELISA)-based binding test was developed to measure ExoU-SOD1 binding. These experiments suggest that ExoU activation by SOD1 is hampered by linker insertion. ExoU derivatives harboring minimal phospholipase activity retained biological activity in tissue culture assays. These proteins affected primarily cellular architecture in a manner similar to that of ExoT. Our studies suggest that conformational changes in ExoU are facilitated by SOD1. Importantly, the level of phospholipase activity influences the biological outcome of ExoU intoxication.

show abstract

“…Complementation restored the mutants to an expected level of virulence, and neither mutant displayed a growth defect on laboratory medium (52). The absence of the other type III effectors secreted by parental strain PA99 (ExoS and ExoT) does not significantly affect the in vitro cytotoxicity or in vivo virulence of ExoU (51).…”

Section: Methodsmentioning

confidence: 97%

Pseudomonas aeruginosa Induces Localized Immunosuppression during Pneumonia

et al. 2008

Self Cite

View full text Add to dashboard Cite

Hospital-acquired bacterial pneumonia is a common and serious complication of modern medical care. Many aspects of such infections remain unclear, including the mechanisms by which invading pathogens resist clearance by the innate immune response and the tendency of the infections to be polymicrobial. Here, we used a mouse model of infection to show that Pseudomonas aeruginosa, a leading cause of hospital-acquired pneumonia, interferes with the ability of recruited phagocytic cells to eradicate bacteria from the lung. Early in infection, phagocytic cells, predominantly neutrophils, are recruited to the lungs but are incapacitated when they enter the airways by the P. aeruginosa toxin ExoU. The resulting paucity of functioning phagocytes allows P. aeruginosa to persist within the lungs and results in local immunosuppression that facilitates superinfection with less-pathogenic bacteria. Together, our results provide explanations for previous reports linking ExoU-secreting P. aeruginosa with more severe pulmonary infections and for the tendency of hospital-acquired pneumonia to be polymicrobial.Hospital-acquired pneumonia (HAP) is a common and frequently lethal complication of admission to an acute medical care facility. HAP infections occur in 0.5 to 2% of hospitalized patients (30,33) and are associated with mortality rates of approximately 30% (6,13,41,54). HAP is usually caused by bacterial pathogens, and in 26 to 67% of cases the etiology is polymicrobial (3,8,39). While the reasons for this are unclear, the coexistence of multiple species of bacteria within the lungs of patients may contribute to the high mortality associated with this disease.The gram-negative bacterium Pseudomonas aeruginosa is the leading cause of HAP in patients undergoing mechanical ventilation (referred to as ventilator-associated pneumonia [VAP]) (40). Interestingly, infection with P. aeruginosa, as opposed to infection with most other bacterial species, is an independent risk factor for death in patients with VAP (23). Although a high incidence of antibiotic resistance among P. aeruginosa strains contributes to the excess mortality associated with this bacterium, its intrinsic virulence also likely plays a role. Even VAP patients treated with antimicrobial agents to which their P. aeruginosa isolates were susceptible had a relapse rate of 18% (42). This suggests that P. aeruginosa elaborates potent virulence determinants that are adept at neutralizing the host immune response, resulting in persistent bacterial infections with poor outcomes.Despite the severity of HAP caused by P. aeruginosa, much remains unknown about the mechanisms by which this bacterium persists in the lungs and causes the tissue damage and inflammation associated with pneumonia. P. aeruginosa elaborates a number of virulence factors that may augment the disease process (12, 45), including a type III secretion system, which has been associated with more-severe disease in patients with HAP (18,44). Via a type III secretion system, some strains of P. aeruginosa injec...

show abstract

Interactions between effector proteins of the Pseudomonas aeruginosa type III secretion system do not significantly affect several measures of disease severity in mammals

Cited by 16 publications

References 66 publications

Pseudomonas aeruginosa Cytotoxin ExoU Is Injected into Phagocytic Cells during Acute Pneumonia

Pseudomonas aeruginosa Cytotoxin ExoU Is Injected into Phagocytic Cells during Acute Pneumonia

Activation of ExoU Phospholipase Activity Requires Specific C-Terminal Regions

Pseudomonas aeruginosa Induces Localized Immunosuppression during Pneumonia

Contact Info

Product

Resources

About