Production of quorum sensing-related metabolites and phytoalexins during Pseudomonas aeruginosa-Brassica napus interaction.

Pseudomonas aeruginosa is an opportunistic bacterial pathogen that has been shown to interact with many organisms throughout the domains of life, including plants. How this broad-host-range bacterium interacts with each of its diverse hosts, especially the metabolites that mediate these interactions, is not completely known. In this work, we used a liquid culture root infection system to collect plant and bacterial metabolites on days 1, 3 and 5 post-P. aeruginosa (strain PA14) infection of the oilseed plant, canola (Brassica napus). Using MS-based metabolomics approaches, we identified the overproduction of quorum sensing (QS)-related (both signalling molecules and regulated products) metabolites by P. aeruginosa while interacting with canola plants. However, the P. aeruginosa infection induced the production of several phytoalexins, which is a part of the hallmark plant defence response to microbes. The QS system of PA14 appears to only mediate part of the canola-P. aeruginosa metabolomic interactions, as the use of isogenic mutant strains of each of the three QS signalling branches did not significantly affect the induction of the phytoalexin brassilexin, while induction of spirobrassinin was significantly decreased. Interestingly, a treatment of purified QS molecules in the absence of bacteria was not able to induce any phytoalexin production, suggesting that active bacterial colonization is required for eliciting phytoalexin production. Furthermore, we identified that brassilexin, the only commercially available phytoalexin that was detected in this study, demonstrated a MIC of 400 µg ml-1 against P. aeruginosa PA14. The production of phytoalexins can be an effective component of canola innate immunity to keep potential infections by the opportunistic pathogen P. aeruginosa at bay.

Non-Canonical Host Intracellular Niche Links to New Antimicrobial Resistance Mechanism.

Globally, infectious diseases are one of the leading causes of death among people of all ages. The development of antimicrobials to treat infectious diseases has been one of the most significant advances in medical history. Alarmingly, antimicrobial resistance is a widespread phenomenon that will, without intervention, make currently treatable infections once again deadly. In an era of widespread antimicrobial resistance, there is a constant and pressing need to develop new antibacterial drugs. Unraveling the underlying resistance mechanisms is critical to fight this crisis. In this review, we summarize some emerging evidence of the non-canonical intracellular life cycle of two priority antimicrobial-resistant bacterial pathogens: Pseudomonas aeruginosa and Staphylococcus aureus. The bacterial factors that modulate this unique intracellular niche and its implications in contributing to resistance are discussed. We then briefly discuss some recent research that focused on the promises of boosting host immunity as a combination therapy with antimicrobials to eradicate these two particular pathogens. Finally, we summarize the importance of various strategies, including surveillance and vaccines, in mitigating the impacts of antimicrobial resistance in general.