Cephalosporins Interfere With Quorum Sensing and Improve the Ability of Caenorhabditis elegans to Survive Pseudomonas aeruginosa Infection

Abstract

Pseudomonas aeruginosa utilizes the quorum sensing (QS) system to strategically coordinate virulence and biofilm formation. Targeting QS pathways may be a potential anti-infective approach to treat P. aeruginosa infections. In the present study, we define cephalosporins’ anti-QS activity using Chromobacterium violaceum CV026 for screening and QS-regulated mutants of P. aeruginosa for validation. We quantified the effects of three cephalosporins, cefepime, ceftazidime, and ceftriaxone, on (1) pyocyanin production using spectrophotometric assay, (2) bacterial motility using agar plate assay, and (3) biofilm formation using scanning electron microscopy. We also studied isogenic QS mutant strains of PAO1 (ΔlasR,ΔrhlR,ΔpqsA, and ΔpqsR) to compare and distinguish QS-mediated effects on the motility phenotypes and bacterial growth with and without sub-MIC concentrations of antibiotics. Results showed that cephalosporins have anti-QS activity and reduce bacterial motility, pyocyanin production, and biofilm formation for CV026 and PAO1. Also, sub-MICs of cefepime increased aminoglycosides’ antimicrobial activity against P. aeruginosa PAO1, suggesting the advantage of combined anti-QS and antibacterial treatment. To correlate experimentally observed anti-QS effects with the interactions between cephalosporins and QS receptors, we performed molecular docking with ligand binding sites of quorum sensing receptors using Autodock Vina. Molecular docking predicted cephalosporins’ binding affinities to the ligand-binding pocket of QS receptors (CviR, LasR, and PqsR). To validate our results using an infection model, we quantified the survival rate of Caenorhabditis elegans following P. aeruginosa PAO1 challenge at concentrations less than the minimum inhibitory concentration (MIC) of antibiotics. C. elegans infected with PAO1 without antibiotics showed 0% survivability after 72 h. In contrast, PAO1-infected C. elegans showed 65 ± 5%, 58 ± 4%, and 49 ± 8% survivability after treatment with cefepime, ceftazidime, and ceftriaxone, respectively. We determined the survival rates of C. elegans infected by QS mutant strains ΔlasR (32 ± 11%), ΔrhlR (27 ± 8%), ΔpqsA (27 ± 10%), and ΔpqsR (37 ± 6%), which suggest essential role of QS system in virulence. In summary, cephalosporins at sub-MIC concentrations show anti-QS activity and enhance the antibacterial efficacy of aminoglycosides, a different class of antibiotics. Thus, cephalosporins at sub-MIC concentrations in combination with other antibiotics are potential candidates for developing therapies to combat infections caused by P. aeruginosa.

New Sesquiterpenoids From Plant-Associated Irpex lacteus

“…The efficacy of purified compounds on inhibiting QS mechanisms was screened using indicator organisms Chromobacterium violaceum CV026 and Agrobacterium tumefaciens A136. Overnight grown C. violaceum CV026 culture (1 ml) (OD 600 ≈ 0.1) was added into 100 ml LB agar medium supplemented with kanamycin (20 μg/ml) and C6-HSL (5 μM), mixed, and poured into the plates ( Kumar et al, 2021 ). After the medium was solidified, 2 μl of samples ( 1–4 ) (50 mg/ml) were dropped onto the plates and then incubated at 28°C for 24 h, recording the violacein changes in color.…”

Peptidomimetics as Potential Anti-Virulence Drugs Against Resistant Bacterial Pathogens

“…The functionality of quorum-sensing systems resides on basic components that are druggable and tend to be absent in mammals ( LaSarre and Federle, 2013 ; Fleitas Martínez et al, 2019b ; Ellermann and Sperandio, 2020 ). Similarly to the observed in bacterial secretion systems, mutant strains in quorum sensing system components could become avirulent strains in infection models ( Askoura et al, 2021 ; Kumar et al, 2021 ). Studies focused on quenching quorum sensing systems with inhibitors have demonstrated that targeting these communication systems is a promising strategy to face resistant pathogens ( Sully et al, 2014 ; Daly et al, 2015 ; Parlet et al, 2019 ; Salam et al, 2021 ; Wang et al, 2021 ).…”

Gentamicin Augments the Quorum Quenching Potential of Cinnamaldehyde In Vitro and Protects Caenorhabditis elegans From Pseudomonas aeruginosa Infection

“…Computational analysis provides an excellent tool to simulate the ligand-receptor interactions at the atomic level ( Kumar et al., 2021 ). Hence, in silico analysis was carried out to gain better insights into the possible associations between CiNN and the QS receptors of P. aeruginosa .…”

“…Since QS functions as an auxiliary factor that promotes pseudomonal virulence, its abrogation using QS inhibitors may possibly minimize the risk of exerting any selection pressure for the emergence of anthropogenic resistance, a phenomenon commonly witnessed with conventional antibiotic therapy ( Rasmussen and Givskov, 2006 ). The fascinating property of a potent quorum quenching (QQ) agent is that it attenuates QS circuits of a pathogen at sub-inhibitory concentrations (sub-MICs) by either degrading the QS molecule or by abrogating its interaction with their cognate receptors without directly targeting the vital pathways required for bacterial survival ( Kumar et al., 2021 ). Since this strategy does not impose any survival threat, the probability of developing resistance against the anti-QS drugs also remains low.…”

“…Their antimicrobial properties have been favored worldwide due to their natural existence, easy and economic availability, formidable pharmacological properties, and negligible cytotoxicity ( Chadha et al., 2021c ). Essential oils (EOs) contain a plethora of volatile secondary metabolites, including aldehydes, flavonoids, terpenoids, phenolics, polyacetylenes, and quinones that exhibit QQ at lower concentrations and antimicrobial properties at higher concentrations ( Kumar et al., 2021 ). Cinnamon, derived from the inner bark of Cinnamomum verum has been long known as a traditional Indian spice and is used habitually in the Asian subcontinent.…”