Blocking the acquisition of the essential iron nutrient in Pseudomonas aeruginosa

Abstract

The Gram-negative opportunistic pathogen Pseudomonas aeruginosa (Pa), declared by the World health organization as a “Priority 1: Critical Pathogen," needs immediate new tactics for developing antipseudomonal treatments. Pa uses mechanisms to acquire ferric, heme (Hm), and ferrous iron from human hosts to survive, colonize and cause infection. Efforts have been made to create siderophore blockers to inhibit the ferric acquisition pathway of Pa. However, a lack of inhibitors exist to block the remaining Hm and ferrous pathways. We developed a targeted high throughput screening (HTS) approach and identified molecules that specifically inhibit the Hm and ferrous acquisition systems. We screened Pa against a small molecule library under three growth conditions. The iron source was the only variable, and each condition served as a counter screen for the other. We were able to identify econazole, bithionate, as growth inhibitors in Hm and oxyquinoline sulfate in ferrous iron. When exposed to meropenem, a commercial antipseudomonal, there was no interference in activity with some increased antipseudomonal activity. We examined each molecule's mechanisms of action to further understand interactions between Pa and the molecules. We also examined the effects of the compounds in the presence of biofilm and drug-resistant clinical isolates both in shaking and static conditions. The majority of the compounds showed specific activity in the respective iron sources against the isolates. Further analysis is needed to examine the mechanisms of action though initial experiments indicate that each compound has unique targets. In conclusion, we presented proof-of-concept of a successful targeted HTS, identified effective iron acquisition inhibitors against clinical isolates and started initial experiments to characterize the mechanisms of action of the newly identified inhibitors.