Exoenzyme Y Contributes to End-Organ Dysfunction Caused by Pseudomonas aeruginosa Pneumonia in Critically Ill Patients: An Exploratory Study

Abstract

Pseudomonas aeruginosa is an opportunistic pathogen that causes pneumonia in immunocompromised and intensive care unit (ICU) patients. During host infection, P. aeruginosa upregulates the type III secretion system (T3SS), which is used to intoxicate host cells with exoenzyme (Exo) virulence factors. Of the four known Exo virulence factors (U, S, T and Y), ExoU has been shown in prior studies to associate with high mortality rates. Preclinical studies have shown that ExoY is an important edema factor in lung infection caused by P. aeruginosa, although its importance in clinical isolates of P. aeruginosa is unknown. We hypothesized that expression of ExoY would be highly prevalent in clinical isolates and would significantly contribute to patient morbidity secondary to P. aeruginosa pneumonia. A single-center, prospective observational study was conducted at the University of Alabama at Birmingham Hospital. Mechanically ventilated ICU patients with a bronchoalveolar lavage fluid culture positive for P. aeruginosa were included. Enrolled patients were followed from ICU admission to discharge and clinical P. aeruginosa isolates were genotyped for the presence of exoenzyme genes. Ninety-nine patients were enrolled in the study. ExoY was present in 93% of P. aeruginosa clinical isolates. Moreover, ExoY alone (ExoY+/ExoU−) was present in 75% of P. aeruginosa isolates, compared to 2% ExoU alone (ExoY−/ExoU+). We found that bacteria isolated from human samples expressed active ExoY and ExoU, and the presence of ExoY in clinical isolates was associated with end-organ dysfunction. This is the first study we are aware of that demonstrates that ExoY is important in clinical outcomes secondary to nosocomial pneumonia.

Pseudomonas aeruginosa: An Audacious Pathogen with an Adaptable Arsenal of Virulence Factors

“…ExoY is the second most prevalent exotoxin, expressed by >89% of isolates [ 113 , 120 ]. It is a soluble adenylate cyclase that elevates the intracellular levels of various cyclic nucleotides (cAMP, cCMP, cGMP, and cUMP) when injected into mammalian cells, activating protein kinases [ 117 , 121 ].…”

“…It is a soluble adenylate cyclase that elevates the intracellular levels of various cyclic nucleotides (cAMP, cCMP, cGMP, and cUMP) when injected into mammalian cells, activating protein kinases [ 117 , 121 ]. Consequently, it causes irreversible actin microtubule disassembly, cell necrosis, and alteration of endothelial barrier integrity, following lung injury and end-organ dysfunction [ 120 , 122 ]. Recently, it was shown that ExoY possesses one actin-binding site that directly bundles actin filaments in the host cell [ 123 ].…”

Mechanism of actin-dependent activation of nucleotidyl cyclase toxins from bacterial human pathogens

“…At lower ExoY concentrations, which are more likely during chronical infection, the activity of PaExoY allows P. aeruginosa to hijack host immune response by a suppression of TAK1 and a decreased production of interleukin 1 (9,10). A recent report has established a link between the presence of PaExoY in clinical isolates and end-organ dysfunction in critically ill patients (11).…”

Prevalence of ExoY Activity in Pseudomonas aeruginosa Reference Panel Strains and Impact on Cytotoxicity in Epithelial Cells

“…In addition, a recent study genotyping P. aeruginosa isolates from 99 critically ill, mechanically ventilated patients, showed a 93% prevalence of the exoY gene. GC activity was verified in vitro from six of the exoY encoding P. aeruginosa isolates by measuring cGMP accumulation in infected cells (Wagener et al, 2020).…”