Pseudomonas aeruginosa PA80 is a cystic fibrosis isolate deficient in RhlRI quorum sensing

The end of the reign of a "master regulator''? A defect in function of the LasR quorum sensing regulator is a common feature of Pseudomonas aeruginosa isolates

Pseudomonas aeruginosa, a bacterium causing infections in immunocompromised individuals, regulates several of its virulence functions using three interlinked quorum sensing (QS) systems (las, rhl, and pqs). Despite its presumed importance in regulating virulence, dysfunction of the las system regulator LasR occurs frequently in strains isolated from various environments, including clinical infections. This newfound abundance of LasR-defective strains calls into question existing hypotheses regarding their selection. Indeed, current assumptions concerning factors driving the emergence of LasR-deficient isolates and the role of LasR in the QS hierarchy must be reconsidered. Here, we propose that LasR is not the primary master regulator of QS in all P. aeruginosa genetic backgrounds, even though it remains ecologically significant. We also revisit and complement current knowledge on the ecology of LasR-dependent QS in P. aeruginosa, discuss the hypotheses explaining the putative adaptive benefits of selecting against LasR function, and consider the implications of this renewed understanding.

Co-occurring microflora and mucin drive Pseudomonas aeruginosa diversification and pathoadaptation

While several environmental factors contribute to the evolutionary diversification of the pathogenic bacterium Pseudomonas aeruginosa during cystic fibrosis lung infections, relatively little is known about the impact of the surrounding microbiota. By using in vitro experimental evolution, we show that the presence of Stenotrophomonas maltophilia, Staphylococcus aureus, or them both, prevent the evolution of loss of virulence, which repeatedly occurs in the absence of these species due to mutations in regulators of the Pseudomonas Quinolone Signal quorum sensing system, vqsM and pqsR. Moreover, the strength of the effect of co-occurring species is attenuated through changes in the physical environment by the addition of mucin, resulting in selection for phenotypes resembling those evolved in the absence of the co-occurring species. Together, our findings show that variation in mucosal environment and the surrounding polymicrobial environment can determine the evolutionary trajectory of P. aeruginosa, partly explaining its diversification and pathoadaptation from acute to chronic phenotype during cystic fibrosis lung infections.

Citrinin Is a Potential Quorum Sensing Inhibitor against Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic pathogen that infects patients by regulating virulence factors and biofilms through a quorum sensing (QS) system to protect itself from antibiotics and environmental stress. Therefore, the development of quorum sensing inhibitors (QSIs) is expected to become a new strategy for studying drug resistance to P. aeruginosa infections. Marine fungi are valuable resources for screening QSIs. A marine fungus, Penicillium sp. JH1, with anti-QS activity was isolated from the offshore waters of Qingdao (China), and citrinin, a novel QSI, was purified from secondary metabolites of this fungus. Citrinin could significantly inhibit the production of violacein in Chromobacterium violaceum CV12472 and the production of three virulence factors (elastase, rhamnolipid and pyocyanin) in P. aeruginosa PAO1. It could also inhibit the biofilm formation and motility of PAO1. In addition, citrinin downregulated the transcript levels of nine genes (lasI, rhlI, pqsA, lasR, rhlR, pqsR, lasB, rhlA and phzH) associated with QS. Molecular docking results showed that citrinin bound to PqsR and LasR with better affinity than the natural ligands. This study laid a foundation for the further study of the structure optimization and structure-activity relationship of citrinin.

Complications and Treatments of Pseudomonas aeruginosa Infection After Rhinoplasty With Implants: A Clinical Study

BACKGROUND

Pseudomonas aeruginosa is an opportunistic pathogen, and because of its specificity, its treatments appear tricky in postrhinoplasty infections with internal implants. This study summarizes the clinical characteristics and treatment of this type of infections to provide some reference for clinical work.

METHODS

We retrospectively analyzed 10 patients who were diagnosed with a nasal infection of P. aeruginosa after implant nasal augmentation. The results of the bacterial culture and drug sensitivity test of the patients' wound secretions were summarized and analyzed. We summarized the characteristics of the patients' infection and the treatments, and we also summarized the patients' prognosis.

RESULTS

In these 10 cases, their implants included rib cartilage and ear cartilage alone, as well as their own cartilage combined with expanded polytetrafluoroethylene and silicone. All patients developed wound infections within 1 month after rhinoplasty, with bacterial cultures of P. aeruginosa . Prolonged use of sensitive antibiotics, as well as wound dressing changes, failed to keep the infection well under control. Patients whose implant was removed and thoroughly debrided within 1 week of infection did not experience any serious complications. In patients who were infected for >1 week before surgery to remove the implants, complications such as nasal column necrosis and nasal contracture occurred, and later the nasal repair was performed after multiple surgeries.

CONCLUSIONS

For bacterial infections in postrhinoplasty wounds with implants, we recommend early bacterial culture. If the infection is clearly P. aeruginosa , the implant should be removed and thoroughly debrided as soon as possible to avoid serious complications.

LEVEL OF EVIDENCE

Level IV.

Reducing the virulence of Pseudomonas aeruginosa by using multiple quorum-quenching enzymes

The emergence of multidrug-resistant Pseudomonas aeruginosa in healthcare settings poses a tremendous challenge to traditional antibiotic therapy. Pseudomonas aeruginosa utilizes quorum sensing (QS) to coordinate the production of virulence factors and the formation of drug-resistant biofilms. QS is mediated by signal compounds produced by P. aeruginosa as well as signal molecules produced by other non-pseudomonad bacteria. A potential strategy to prevent bacterial pathogenicity is utilizing enzymes to interfere with QS. Here, we used AidC, a quorum-quenching (QQ) enzyme from Chryseobacterium sp. strain StRB126 that can effectively hydrolyze N-(3-oxododecanoyl) homoserine lactone (3OC12-HSL) and N-butanoyl-homoserine lactone (C4-HSL), the major signal molecules synthesized by P. aeruginosa. The exogenous addition of AidC to P. aeruginosa wild-type strain PAO1 cultures significantly reduced the total protease and elastase activities and the production of pyocyanin. In addition, the application of AidC resulted in thin and sparse biofilm formation. Later, we used a metagenomic-derived QQ enzyme, QQ-2, in combination with AidC to attenuate PAO1 virulence when the presence of a non-pseudomonad signal compound, autoinducer-2, aggravated it. These findings suggest that using a combined antimicrobial approach may lead to a more efficacious therapeutic intervention against P. aeruginosa PAO1 infection, as its behavior is modulated in the presence of intraspecies and interspecies signal compounds.

ONE-SENTENCE SUMMARY

In this work, the potential of dual enzymes was investigated to interfere with quorum sensing as a novel concept for reducing the virulence of P. aeruginosa, which is influenced by both intra species and interspecies communication.

Evolution of Quorum Sensing in Pseudomonas aeruginosa Can Occur via Loss of Function and Regulon Modulation

Pseudomonas aeruginosa populations evolving in cystic fibrosis lungs, animal hosts, natural environments and in vitro undergo extensive genetic adaption and diversification. A common mutational target is the quorum sensing (QS) system, a three-unit regulatory system that controls the expression of virulence factors and secreted public goods. Three evolutionary scenarios have been advocated to explain selection for QS mutants: (i) disuse of the regulon, (ii) cheating through the exploitation of public goods, or (ii) modulation of the QS regulon. Here, we examine these scenarios by studying a set of 61 QS mutants from an experimental evolution study. We observed nonsynonymous mutations in all three QS systems: Las, Rhl, and Pseudomonas Quinolone Signal (PQS). The majority of the Las mutants had large deletions of the Las regulon, resulting in loss of QS function and the inability to produce QS-regulated traits, thus supporting the first or second scenarios. Conversely, phenotypic and gene expression analyses of Rhl mutants support network modulation (third scenario), as these mutants overexpressed the Las and Rhl receptors and showed an altered QS-regulated trait production profile. PQS mutants also showed patterns of regulon modulation leading to strain diversification and phenotypic tradeoffs, where the upregulation of certain QS traits is associated with the downregulation of others. Overall, our results indicate that mutations in the different QS systems lead to diverging effects on the QS trait profile in P. aeruginosa populations. These mutations might not only affect the plasticity and diversity of evolved populations but could also impact bacterial fitness and virulence in infections. IMPORTANCE Pseudomonas aeruginosa uses quorum sensing (QS), a three-unit multilayered network, to coordinate expression of traits required for growth and virulence in the context of infections. Despite its importance for bacterial fitness, the QS regulon appears to be a common mutational target during long-term adaptation of P. aeruginosa in the host, natural environments, and experimental evolutions. This raises questions of why such an important regulatory system is under selection and how mutations change the profile of QS-regulated traits. Here, we examine a set of 61 experimentally evolved QS mutants to address these questions. We found that mutations involving the master regulator, LasR, resulted in an almost complete breakdown of QS, while mutations in RhlR and PqsR resulted in modulations of the regulon, where both the regulon structure and the QS-regulated trait profile changed. Our work reveals that natural selection drives diversification in QS activity patterns in evolving populations.