Evaluating the effect of antibiotics sub-inhibitory dose on Pseudomonas aeruginosa quorum sensing dependent virulence and its phenotypes

Repurposing ebselen as an inhalable dry powder to treat respiratory tract infections

Respiratory tract infections (RTIs) are one of the leading causes of death globally, lately exacerbated by the increasing prevalence of antimicrobial resistance. While antimicrobial resistance could be overcome by developing new antimicrobial agents, the use of a safe repurposed agent having potent antimicrobial activity against various RTIs can be an efficient and cost-effective alternative to overcome the long and complex process of developing and testing new drugs. Ebselen, a synthetic organoselenium drug originally developed to treat noise-inducing hearing problems, has shown promising antimicrobial activity in vitro against several respiratory pathogens including viruses (e.g., SARS-CoV-2, influenza A virus) and bacteria (e.g., Mycobacterium tuberculosis, Streptococcus pneumoniae, and Staphylococcus aureus). Inhaled drug delivery is considered a promising approach for treating RTIs, as it can ensure effective drug concentrations at a lower dose, thereby minimizing the side effects that are often encountered by using oral or injectable drugs. In this study, we developed inhalable ebselen dry powder formulations using a spray-drying technique. The amino acids leucine, methionine, and tryptophan were incorporated with ebselen to enhance the yield and aerosolization of the dry powders. The amino acid-containing ebselen dry powders showed a better yield (37-56.4 %) than the amino acid-free formulation (30.9 %). All dry powders were crystalline in nature. The mass median aerodynamic diameter (MMAD) was less than 5 µm for amino acids containing dry powders (3-4 µm) and slightly higher (5.4 µm) for amino acid free dry powder indicating their suitability for inhalation. The aerosol performance was higher when amino acids were used, and the leucine-containing ebselen dry powder showed the highest emitted dose (84 %) and fine particle fraction (68 %). All amino acid formulations had similar cytotoxicity as raw ebselen, tested in respiratory cell line (A549 cells), with half-maximal inhibitory concentrations (IC50) between 100 and 250 μg/mL. Raw ebselen and amino acid-containing dry powders showed similar potent antibacterial activity against the Gram-positive bacteria S. aureus and S. pneumoniae with minimum inhibitory concentrations of 0.31 μg/mL and 0.16 μg/mL, respectively. On the other hand, raw ebselen and the formulations showed limited antimicrobial activity against the Gram-negative pathogens Pseudomonas aeruginosa and Klebsiella pneumoniae. In summary, in this study we were able to develop amino-acid-containing inhalable dry powders of ebselen that could be used against different respiratory pathogens, especially Gram-positive bacteria, which could ensure more drug deposition in the respiratory tract, including the lungs. DPIs are generally used to treat lung (lower respiratory tract) diseases. However, DPIs can also be used to treat both upper and lower RTIs. The deposition of the dry powder in the respiratory tract is dependent on its physicochemical properties and this properties can be modulated to target the intended site of infection (upper and/or lower respiratory tract). Further studies will allow the development of similar formulations of individual and/or combination of antimicrobials that could be used to inhibit a number of respiratory pathogens.

Synergistic effect of kanamycin and amikacin with setomimycin on biofilm formation inhibition of Listeria monocytogenes

Listeria monocytogenes, a foodborne pathogen that causes listeriosis with high fatality rate, exhibits multidrug resistance (MDR) known to be progressively increasing. Alternative antibacterial strategies are in high demand for treating this well-known pathogen. Anti-biofilm and anti-virulence strategies are being explored as novel approaches to treat bacterial infections. In this study, one rare antibacterial named setomimycin was isolated from Streptomyces cyaneochromogenes, which showed potent antibacterial activity against L. monocytogenes. Next, the inhibition of biofilm formation and listeriolysin O (LLO) production against L. monocytogenes were investigated at sub-minimal inhibitory concentrations (sub-MICs) of setomimycin alone or combined with kanamycin and amikacin. Crystal violet staining confirmed that setomimycin combining with kanamycin or amikacin could dramatically reduce biofilm formation against L. monocytogenes at sub-MICs, which was further evaluated by scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). In the meantime, sub-MICs of setomimycin could significantly suppress the secretion of LLO. Furthermore, the transcription of genes associated with biofilms and main virulence factors, such as LLO, flagellum, and metalloprotease, were suppressed by setomimycin at sub-MICs. Hence, the study provided a deep insight into setomimycin as an alternative antibacterial agent against L. monocytogenes.

Attenuation of Pseudomonas aeruginosa Quorum Sensing Virulence of Biofilm and Pyocyanin by mBTL-Loaded Calcium Alginate Nanoparticles

Pseudomonas aeruginosa contributes to many chronic infections and has been found to be resistant to multiple antibiotics. Pseudomonas use a quorum sensing system (QS) to control biofilm establishment and virulence factors, and, thus, quorum sensing inhibitors (QSIs), such as meta-bromo-thiolactone (mBTL), are promising anti-infective agents. Accordingly, this study intended to investigate the antibacterial and anti-virulence activity of mBTL-loaded calcium alginate nanoparticles (CANPs) against Pseudomonas aeruginosa and different QS mutants. The results show that the mBTL-CANPs had higher antibacterial activity, which was made evident by decreases in all tested strains except the ∆lasR/∆rhlR double mutant, with MIC₅₀ (0.5 mg/mL) of mBTL-CANPs compared with free mBTL at MIC₅₀ (˃1 mg/mL). The biofilm formation of P. aeruginosa and some QS-deficient mutants were reduced in response to 0.5-0.125 mg/mL of mBTL-encapsulating CANPs. The pyocyanin production of the tested strains except ∆lasA and ∆rhlR decreased when challenged with 0.5 mg/mL of mBTL-loaded NPs. The subsequent characterization of the cytotoxic effect of these NPs on human lung epithelial cells (A549) and cystic fibrosis fibroblast cells (LL 29) demonstrated that synthesized NPs were cytocompatible at MIC₅₀ in both cell lines and markedly reduced the cytotoxic effect observed with mBTL alone on these cells. The resulting formulation reduced the P. aeruginosa strains' adhesion to A549 comparably with mBTL, suggesting their potential anti-adhesive effect. Given the virulence suppressing action, cytocompatibility, and enhanced anti-biofilm effect of mBTL-CANPs, and the advantage of alginate-based NPs as an antimicrobial delivery system these nanoparticles have great potential in the prophylaxis and treatment of infection caused by Pseudomonas aeruginosa.

Structural and Metabolic Profiling of Lycopersicon esculentum Rhizosphere Microbiota Artificially Exposed at Commonly Used Non-Steroidal Anti-Inflammatory Drugs

In this study, the effect of common non-steroidal anti-inflammatory drugs on Lycopersicon esculentum rhizosphere microbiota was monitored. The experiments were performed with artificially contaminated soil with ibuprofen (0.5 mg·kg⁻¹), ketoprofen (0.2 mg·kg⁻¹) and diclofenac (0.7 mg·kg⁻¹). The results evidenced that the rhizosphere microbiota abundance decreased especially under exposure to diclofenac (187–201 nmol·g⁻¹ dry weight soil) and ibuprofen (166–183 nmol·g⁻¹ dry weight soil) if compared with control (185–240 nmol·g⁻¹ dry weight soil), while the fungal/bacteria ratio changed significantly with exposure to diclofenac (<27%) and ketoprofen (<18%). Compared with control samples, the average amount of the ratio of Gram-negative/Gram-positive bacteria was higher in rhizosphere soil contaminated with ibuprofen (>25%) and lower in the case of diclofenac (<46%) contamination. Carbon source consumption increased with the time of assay in case of the control samples (23%) and those contaminated with diclofenac (8%). This suggests that rhizosphere microbiota under contamination with diclofenac consume a higher amount of carbon, but they do not consume a larger variety of its sources. In the case of contamination with ibuprofen and ketoprofen, the consumption of carbon source presents a decreasing tendency after day 30 of the assay. Rhizosphere microbiota emitting volatile organic compounds were also monitored. Volatile compounds belonging to alcohol, aromatic compounds, ketone, terpene, organic acids, aldehyde, sulphur compounds, esters, alkane, nitrogen compounds, alkene and furans were detected in rhizosphere soil samples. Among these, terpene, ketone, alcohol, aromatic compounds, organic acids and alkane were the most abundant compound classes (>75%), but their percentage changed with exposure to diclofenac, ketoprofen and ibuprofen. Such changes in abundance, structure and the metabolic activity of Lycopersicon esculentum rhizosphere microbiota under exposure to common non-steroidal anti-inflammatory drugs suggest that there is a probability to also change the ecosystem services provided by rhizosphere microbiota.

Quorum Sensing Inhibiting Activity of Cefoperazone and Its Metallic Derivatives on Pseudomonas aeruginosa

The last decade has witnessed a massive increase in the rate of mortalities caused by multidrug-resistant Pseudomonas aeruginosa. Therefore, developing new strategies to control virulence factors and pathogenicity has received much attention. One of these strategies is quorum sensing inhibition (QSI) which was developed to control Pseudomonas infection. This study aims to validate the effect of one of the most used β-lactam antibiotics; cefoperazone (CFP) and its metallic-derivatives on quorum sensing (QS) and virulence factors of P. aeruginosa. Assessment of quorum sensing inhibitory activity of CFP, cefoperazone Iron complex (CFPF) and cefoperazone Cobalt complex (CFPC) was performed by using reporter strain Chromobacterium violaceum ATCC 12472. Minimal inhibitory concentration (MIC) was carried out by the microbroth dilution method. The influence of sub-MICs (1/4 and 1/2 MICs) of CFP, CFPF and CFPC on virulence factors of P. aeruginosa was evaluated. Data was confirmed on the molecular level by RT-PCR. Also, molecular docking analysis was conducted to figure out the possible mechanisms of QSI. CFP, CFPF, and CFPC inhibited violacein pigment production of C. violaceum ATCC 12472. Sub-MICs of CFP (128- 256 μg/mL), and significantly low concentrations of CFPC (0.5- 16 μg/mL) and CFPF (0.5- 64 μg/mL) reduced the production of QS related virulence factors such as pyocyanin, protease, hemolysin and eliminated biofilm assembly by P. aeruginosa standard strains PAO1 and PA14, and P. aeruginosa clinical isolates Ps1, Ps2, and Ps3, without affecting bacterial viability. In addition, CFP, CFPF, and CFPC significantly reduced the expression of lasI and rhlI genes. The molecular docking analysis elucidated that the QS inhibitory effect was possibly caused by the interaction with QS receptors. Both CFPF and CFPC interacted strongly with LasI, LasR and PqsR receptors with a much high ICM scores compared to CFP that could be the cause of elimination of natural ligand binding. Therefore, CFPC and CFPF are potent inhibitors of quorum sensing signaling and virulence factors of P. aeruginosa.

No Correlation between Biofilm Formation, Virulence Factors, and Antibiotic Resistance in Pseudomonas aeruginosa: Results from a Laboratory-Based In Vitro Study

Pseudomonas aeruginosa (P. aeruginosa) possesses a plethora of virulence determinants, including the production of biofilm, pigments, exotoxins, proteases, flagella, and secretion systems. The aim of our present study was to establish the relationship between biofilm-forming capacity, the expression of some important virulence factors, and the multidrug-resistant (MDR) phenotype in P. aeruginosa. A total of three hundred and two (n = 302) isolates were included in this study. Antimicrobial susceptibility testing and phenotypic detection of resistance determinants were carried out; based on these results, isolates were grouped into distinct resistotypes and multiple antibiotic resistance (MAR) indices were calculated. The capacity of isolates to produce biofilm was assessed using a crystal violet microtiter-plate based method. Motility (swimming, swarming, and twitching) and pigment-production (pyoverdine and pyocyanin) were also measured. Pearson correlation coefficients (r) were calculated to determine for antimicrobial resistance, biofilm-formation, and expression of other virulence factors. Resistance rates were the highest for ceftazidime (56.95%; n = 172), levofloxacin (54.97%; n = 166), and ciprofloxacin (54.64%; n = 159), while lowest for colistin (1.66%; n = 5); 44.04% (n = 133) of isolates were classified as MDR. 19.87% (n = 60), 20.86% (n = 63) and 59.27% (n = 179) were classified as weak, moderate, and strong biofilm producers, respectively. With the exception of pyocyanin production (0.371 ± 0.193 vs. non-MDR: 0.319 ± 0.191; p = 0.018), MDR and non-MDR isolates did not show significant differences in expression of virulence factors. Additionally, no relevant correlations were seen between the rate of biofilm formation, pigment production, or motility. Data on interplay between the presence and mechanisms of drug resistance with those of biofilm formation and virulence is crucial to address chronic bacterial infections and to provide strategies for their management.

It's Not Easy Being Green: A Narrative Review on the Microbiology, Virulence and Therapeutic Prospects of Multidrug-Resistant Pseudomonas aeruginosa

Pseudomonas aeruginosa is the most frequent cause of infection among non-fermenting Gram-negative bacteria, predominantly affecting immunocompromised patients, but its pathogenic role should not be disregarded in immunocompetent patients. These pathogens present a concerning therapeutic challenge to clinicians, both in community and in hospital settings, due to their increasing prevalence of resistance, and this may lead to prolonged therapy, sequelae, and excess mortality in the affected patient population. The resistance mechanisms of P. aeruginosa may be classified into intrinsic and acquired resistance mechanisms. These mechanisms lead to occurrence of resistant strains against important antibiotics-relevant in the treatment of P. aeruginosa infections-such as β-lactams, quinolones, aminoglycosides, and colistin. The occurrence of a specific resistotype of P. aeruginosa, namely the emergence of carbapenem-resistant but cephalosporin-susceptible (Car-R/Ceph-S) strains, has received substantial attention from clinical microbiologists and infection control specialists; nevertheless, the available literature on this topic is still scarce. The aim of this present review paper is to provide a concise summary on the adaptability, virulence, and antibiotic resistance of P. aeruginosa to a readership of basic scientists and clinicians.