In Silico and In Vitro Screening of Antipathogenic Properties of Melianthus comosus (Vahl) against Pseudomonas aeruginosa

Molecular modelling of SdiA protein by selected flavonoid and terpenes compounds to attenuate virulence in Klebsiella pneumoniae

Klebsiella pneumoniae is one of the perturbing multidrug resistant (MDR) and ESKAPE pathogens contributing to the mounting morbidity, mortality and extended rate of hospitalization. Its virulence, often regulated by quorum sensing (QS) reinforces the need to explore alternative and prospective antivirulence agents, relatively from plants secondary metabolites. Computer aided drug discovery using molecular modelling techniques offers advantage to investigate prospective drugs to combat MDR pathogens. Thus, this study employed virtual screening of selected terpenes and flavonoids from medicinal plants to interrupt the QS associated SdiA protein in K. pneumoniae to attenuate its virulence. 4LFU was used as a template to model the structure of SdiA. ProCheck, Verify3D, Ramachandran plot scores, and ProSA-Web all attested to the model's good quality. Since SdiA protein in K. pneumoniae leads to the expression of virulence, 31 prospective bioactive compounds were docked for antagonistic potential. The stability of the protein-ligand complex, atomic motions and inter-atomic interactions were further investigated through molecular dynamics simulations (MDS) at 100 ns production runs. The binding free energy was estimated using the molecular mechanics/poisson-boltzmann surface area (MM/PB-SA). Furthermore, the drug-likeness properties of the studied compounds were validated. Docking studies showed phytol possesses the highest binding affinity (-9.205 kcal/mol) while glycitein had -9.752 kcal/mol highest docking score. The MDS of the protein in complex with the best-docked compounds revealed phytol with the highest binding energy of -44.2625 kcal/mol, a low root-mean-square deviation (RMSD) value of 1.54 Å and root-mean-square fluctuation (RMSF) score of 1.78 Å. Analysis of the drug-likeness properties prediction and bioavailability of these compounds revealed their conformed activity to lipinski's rules with bioavailability scores of 0.55 F. The studied terpenes and flavonoids compounds effectively thwart SdiA protein, therefore regulate inter- or intra cellular communication and associated in virulence Enterobacteriaceae, serving as prospective antivirulence drugs.Communicated by Ramaswamy H. Sarma.

Extracts of Selected South African Medicinal Plants Mitigate Virulence Factors in Multidrug-Resistant Strains of Klebsiella pneumoniae

The emergence of multidrug-resistant (MDR) Klebsiella pneumoniae remains a global health threat due to its alarming rates of becoming resistant to antibiotics. Therefore, identifying plant-based treatment options to target this pathogen's virulence factors is a priority. This study examined the antivirulence activities of twelve plant extracts obtained from three South African medicinal plants (Lippia javanica, Carpobrotus dimidiatus, and Helichrysum populifolium) against carbapenem-resistant (CBR) and extended-spectrum beta-lactamase (ESBL) positive K. pneumoniae strains. The plant extracts (ethyl acetate, dichloromethane, methanol, and water) were validated for their inhibitory activities against bacterial growth and virulence factors such as biofilm formation, exopolysaccharide (EPS) production, curli expression, and hypermucoviscosity. The potent extract on K. pneumoniae biofilm was observed with a scanning electron microscope (SEM), while exopolysaccharide topography and surface parameters were observed using atomic force microscopy (AFM). Chemical profiling of the potent extract in vitro was analysed using liquid chromatography-mass spectrometry (LC-MS). Results revealed a noteworthy minimum inhibitory concentration (MIC) value for the C. dimidiatus dichloromethane extract at 0.78 mg/mL on CBR- K. pneumoniae. L. javanica (ethyl acetate) showed the highest cell attachment inhibition (67.25%) for CBR- K. pneumoniae. SEM correlated the in-vitro findings, evidenced by a significant alteration of the biofilm architecture. The highest EPS reduction of 34.18% was also noted for L. javanica (ethyl acetate) and correlated by noticeable changes observed using AFM. L. javanica (ethyl acetate) further reduced hypermucoviscosity to the least length mucoid string (1 mm-2 mm) at 1.00 mg/mL on both strains. C. dimidiatus (aqueous) showed biofilm inhibition of 45.91% for the ESBL-positive K. pneumoniae and inhibited curli expression at 0.50 mg/mL in both K. pneumoniae strains as observed for H. populifolium (aqueous) extract. Chemical profiling of L. javanica (ethyl acetate), C. dimidiatus (aqueous), and H. populifolium (aqueous) identified diterpene (10.29%), hydroxy-dimethoxyflavone (10.24%), and 4,5-dicaffeoylquinic acid (13.41%), respectively, as dominant compounds. Overall, the ethyl acetate extract of L. javanica revealed potent antivirulence properties against the studied MDR K. pneumoniae strains. Hence, it is a promising medicinal plant that can be investigated further to develop alternative therapy for managing K. pneumoniae-associated infections.

Evolving biofilm inhibition and eradication in clinical settings through plant-based antibiofilm agents

BACKGROUND

After almost 100 years since evidence of biofilm mode of growth and decades of intensive investigation about their formation, regulatory pathways and mechanisms of antimicrobial tolerance, nowadays there are still no therapeutic solutions to eradicate bacterial biofilms and their biomedical related issues.

PURPOSE

This review intends to provide a comprehensive summary of the recent and most relevant published studies on plant-based products, or their isolated compounds with antibiofilm activity mechanisms of action or identified molecular targets against bacterial biofilms. The objective is to offer a new perspective of most recent data for clinical researchers aiming to prevent or eliminate biofilm-associated infections caused by bacterial pathogens.

METHODS

The search was performed considering original research articles published on PubMed, Web of Science and Scopus from 2015 to April 2023, using keywords such as "antibiofilm", "antivirulence", "phytochemicals" and "plant extracts".

RESULTS

Over 180 articles were considered for this review with a focus on the priority human pathogens listed by World Health Organization, including Pseudomonas aeruginosa, Staphylococcus aureus, Klebsiella pneumoniae and Escherichia coli. Inhibition and detachment or dismantling of biofilms formed by these pathogens were found using plant-based extract/products or derivative compounds. Although combination of plant-based products and antibiotics were recorded and discussed, this topic is currently poorly explored and only for a reduced number of bacterial species.

CONCLUSIONS

This review clearly demonstrates that plant-based products or derivative compounds may be a promising therapeutic strategy to eliminate bacterial biofilms and their associated infections. After thoroughly reviewing the vast amount of research carried out over years, it was concluded that plant-based products are mostly able to prevent biofilm formation through inhibition of quorum sensing signals, but also to disrupt mature biofilms developed by multidrug resistant bacteria targeting the biofilm extracellular polymeric substance. Flavonoids and phenolic compounds seemed the most effective against bacterial biofilms.

Ecofriendly phytosynthesized zirconium oxide nanoparticles as antibiofilm and quorum quenching agents against Acinetobacter baumannii

The worldwide increase of multi-drug resistance has directed the researchers to focus on ecofriendly ways of nanoparticles synthesis with effective antivirulence properties. Here, we report the antibiofilm and quorum quenching potential of zirconium oxide nanoparticles (ZrO₂ NPs) synthesized from aqueous ginger extract against multi drug resistant (MDR) Acinetobacter baumannii. The results indicated that ZrO₂ NPs were of tetragonal shape with average diameter of 16 nm. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values for A. baumannii were 15.6 µg/ml and 62.5 µg/ml respectively as revealed by broth microdilution assay. Exposure of bacterial cells to ZrO₂ NPs resulted in reactive oxygen species (ROS) generation which in turn led to cellular membrane disruption as observed by an increase in leakage of cellular contents such as proteins, sugars and DNA. The antibiofilm activity was evaluated by microtiter plate assay and the results revealed that the percentage inhibition of biofilm was found to be 14.3-80.6%. ZrO₂ NPs also obstructed the chemical composition of biofilms matrix by reducing the proteins and carbohydrate contents. Molecular docking studies of ZrO₂ NPs with four proteins (2NAZ, 4HKG, 5D6H and 5HM6) involved in biofilm formation of A. baumannii revealed the interaction of zirconium with target proteins. These findings suggested the in vitro efficacy of phytosynthesized ZrO₂ NPs as antibiofilm and quorum quenching agents that can be exploited in the development of alternative therapeutic options against MDR A. baumannii.

Anti-Biofilm and Associated Anti-Virulence Activities of Selected Phytochemical Compounds against Klebsiella pneumoniae

The ability of Klebsiella pneumoniae to form biofilm renders the pathogen recalcitrant to various antibiotics. The difficulty in managing K. pneumoniae related chronic infections is due to its biofilm-forming ability and associated virulence factors, necessitating the development of efficient strategies to control virulence factors. This study aimed at evaluating the inhibitory potential of selected phytochemical compounds on biofilm-associated virulence factors in K. pneumoniae, as well as authenticating their antibiofilm activity. Five phytochemical compounds (alpha-terpinene, camphene, fisetin, glycitein and phytol) were evaluated for their antibacterial and anti-biofilm-associated virulence factors such as exopolysaccharides, curli fibers, and hypermucoviscosity against carbapenem-resistant and extended-spectrum beta-lactamase-positive K. pneumoniae strains. The antibiofilm potential of these compounds was evaluated at initial cell attachment, microcolony formation and mature biofilm formation, then validated by in situ visualization using scanning electron microscopy (SEM). Exopolysaccharide surface topography was characterized using atomic force microscopy (AFM). The antibacterial activity of the compounds confirmed fisetin as the best anti-carbapenem-resistant K. pneumoniae, demonstrating a minimum inhibitory concentration (MIC) value of 0.0625 mg/mL. Phytol, glycitein and α-terpinene showed MIC values of 0.125 mg/mL for both strains. The assessment of the compounds for anti-virulence activity (exopolysaccharide reduction) revealed an up to 65.91% reduction in phytol and camphene. Atomic force microscopy detected marked differences between the topographies of untreated and treated (camphene and phytol) exopolysaccharides. Curli expression was inhibited at both 0.5 and 1.0 mg/mL by phytol, glycitein, fisetin and quercetin. The hypermucoviscosity was reduced by phytol, glycitein, and fisetin to the shortest mucoid string (1 mm) at 1 mg/mL. Phytol showed the highest antiadhesion activity against carbapenem-resistant and extended-spectrum beta-lactamase-positive K. pneumoniae (54.71% and 50.05%), respectively. Scanning electron microscopy correlated the in vitro findings, with phytol significantly altering the biofilm architecture. Phytol has antibiofilm and antivirulence potential against the highly virulent K. pneumoniae strains, revealing it as a potential lead compound for the management of K. pneumoniae-associated infections.

Pseudomonas aeruginosa Detection Using Conventional PCR and Quantitative Real-Time PCR Based on Species-Specific Novel Gene Targets Identified by Pangenome Analysis

Mining novel specific molecular targets and establishing efficient identification methods are significant for detecting Pseudomonas aeruginosa, which can enable P. aeruginosa tracing in food and water. Pangenome analysis was used to analyze the whole genomic sequences of 2017 strains (including 1,000 P. aeruginosa strains and 1,017 other common foodborne pathogen strains) downloaded from gene databases to obtain novel species-specific genes, yielding a total of 11 such genes. Four novel target genes, UCBPP-PA14_00095, UCBPP-PA14_03237, UCBPP-PA14_04976, and UCBPP-PA14_03627, were selected for use, which had 100% coverage in the target strain and were not present in nontarget bacteria. PCR primers (PA1, PA2, PA3, and PA4) and qPCR primers (PA12, PA13, PA14, and PA15) were designed based on these target genes to establish detection methods. For the PCR primer set, the minimum detection limit for DNA was 65.4 fg/μl, which was observed for primer set PA2 of the UCBPP-PA14_03237 gene. The detection limit in pure culture without pre-enrichment was 10⁵ colony-forming units (CFU)/ml for primer set PA1, 10³ CFU/ml for primer set PA2, and 10⁴ CFU/ml for primer set PA3 and primer set PA4. Then, qPCR standard curves were established based on the novel species-specific targets. The standard curves showed perfect linear correlations, with R² values of 0.9901 for primer set PA12, 0.9915 for primer set PA13, 0.9924 for primer set PA14, and 0.9935 for primer set PA15. The minimum detection limit of the real-time PCR (qPCR) assay was 10² CFU/ml for pure cultures of P. aeruginosa. Compared with the endpoint PCR and traditional culture methods, the qPCR assay was more sensitive by one or two orders of magnitude. The feasibility of these methods was satisfactory in terms of sensitivity, specificity, and efficiency after evaluating 29 ready-to-eat vegetable samples and was almost consistent with that of the national standard detection method. The developed assays can be applied for rapid screening and detection of pathogenic P. aeruginosa, providing accurate results to inform effective monitoring measures in order to improve microbiological safety.

An Andrographolide from Helichrysum caespitium (DC.) Sond. Ex Harv., (Asteraceae) and Its Antimicrobial, Antiquorum Sensing, and Antibiofilm Potentials

Helichrysum caespititium (DC.) Sond. Ex Harv., (Asteraceae) is a medicinal plant indigenous to South Africa. Its non-polar extracts exhibit significant antimicrobial and, in particular, antigonorrheal activity. This study aimed at isolating and purifying the active antigonorrheal compound from its chloroform extract and validating its inhibition potential on quorum sensing (QS) and biofilm formation of multi-drug resistant (MDR) pathogens. Phytochemical investigation of aerial parts of H. caespititium afforded a diterpene lactone (CF6). The effect of CF6 on violacein production and biofilm formation was studied using in vitro quantitative violacein inhibition (Chromobacterium violaceum) and biofilm formation (Streptococcus pyogenes, Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Neisseria gonorrhoeae, and Pseudomonas aeruginosa). The structure of CF6 was characterized using FTIR, NMR, and UPLC-MS data accordingly, as 10-methyl-8-(propan-17-ylidene)naphthalen-9-yl)-11-vinyl-14-hydroxyfuran-16-one. The susceptibility testing of the pathogens against CF6 revealed Neisseria gonorrhoeae was noticeably susceptible with a MIC value of 60 µg/mL, while Streptococcus pyogenes and Staphylococcus aureus showed MIC of 125 µg/mL. All gram-negative pathogens, Escherichia coli, Klebsiella pneumonia and Pseudomonas aeruginosa were inhibited at 250 µg/mL. CF6 also inhibited the production of violacein by 51.88% at 250 µg/mL and prevented cell attachment by 40.76-81.18%, with N. gonorrhoeae being highly prohibited from forming biofilm. In conclusion, 10-methyl-8-(propan-17-ylidene)naphthalen-9-yl)-11-vinyl-14-hydroxyfuran-16-one is the first of its kind to be isolated from the non-polar (chloroform) extract of South African Helichrysum caespititium with antigonorrheal, antimicrobial, antiquorum sensing, and antibiofilm properties. The compound may serve as a drug candidate against MDR pathogens.