Detection of New Quorum Sensing N-Acyl Homoserine Lactones From Aeromonas veronii

Anti-virulence prospects of Metformin against Pseudomonas aeruginosa: A new dimension to a multifaceted drug

Metformin (MeT) is an FDA-approved drug with a myriad of health benefits. Besides being used as an anti-diabetic drug, MeT is also effective against various cancers, liver-, cardiovascular-, and renal diseases. This study was undertaken to examine its unique potential as an anti-virulence drug against an opportunistic bacterial pathogen, Pseudomonas aeruginosa. Due to the menace of multidrug resistance in pathogenic microorganisms, many novel or repurposed drugs with anti-virulence prospects are emerging as next-generation therapies with the aim to overshadow the application of existing antimicrobial regimens. The quorum sensing (QS) mechanisms of P. aeruginosa are an attractive drug target for attenuating bacterial virulence. In this context, the anti-QS potential of MeT was scrutinized using biosensor assays. MeT was comprehensively evaluated for its effects on different motility phenotypes, virulence factor production (phenotypic and genotypic expression) along with biofilm development in P. aeruginosa in vitro. At sub-lethal concentrations, MeT displayed prolific quorum quenching (QQ) ability and remarkably inhibited AHL biosynthesis in P. aeruginosa. Moreover, MeT (1/8 MIC) effectively downregulated the expression levels of various QS- and virulence genes in P. aeruginosa, which coincided with a notable reduction in the levels of alginate, hemolysin, pyocyanin, pyochelin, elastase, and protease production. In silico analysis through molecular docking also predicted strong associations between MeT and QS receptors of P. aeruginosa. MeT also compromised the motility phenotypes and successfully abrogated biofilm formation by inhibiting EPS production in P. aeruginosa. Hence, MeT may be repurposed as an anti-virulence drug against P. aeruginosa in clinical settings.

Quorum sensing-mediated microbial interactions: Mechanisms, applications, challenges and perspectives

Microbial community in natural or artificial environments playes critical roles in substance cycles, products synthesis and species evolution. Although microbial community structures have been revealed via culture-dependent and culture-independent approaches, the hidden forces driving the microbial community are rarely systematically discussed. As a mode of cell-to-cell communication that modifies microbial interactions, quorum sensing can regulate biofilm formation, public goods secretion, and antimicrobial substances synthesis, directly or indirectly influencing microbial community to adapt to the changing environment. Therefore, the current review focuses on microbial community in the different habitats from the quorum sensing perspective. Firstly, the definition and classification of quorum sensing were simply introduced. Subsequently, the relationships between quorum sensing and microbial interactions were deeply explored. The latest progressives regarding the applications of quorum sensing in wastewater treatment, human health, food fermentation, and synthetic biology were summarized in detail. Finally, the bottlenecks and outlooks of quorum sensing driving microbial community were adequately discussed. To our knowledge, this current review is the first to reveal the driving force of microbial community from the quorum sensing perspective. Hopefully, this review provides a theoretical basis for developing effective and convenient approaches to control the microbial community with quorum sensing approaches.

α-Terpineol synergizes with gentamicin to rescue Caenorhabditis elegans from Pseudomonas aeruginosa infection by attenuating quorum sensing-regulated virulence

AIMS

This study scrutinized α-Terpineol (α-T) for its anti-virulence and anti-fouling potential against P. aeruginosa PAO1 in conjunction with gentamicin (GeN) using in-vitro, in-silico, and in-vivo approaches.

MAIN METHODS

The quorum quenching (QQ) potential of the drug combination was studied using a quorum sensing (QS) biosensor strain and tested for synergy using chequerboard and time-kill kinetics assays. The effect of α-T and GeN on bacterial motility, QS-regulated virulence factor production, and biofilm formation was assessed in P. aeruginosa PAO1 along with molecular docking analysis. The protective effects of α-T-GeN combination were also examined in a Caenorhabditis elegans infection model through slow-killing (SK) assays.

KEY FINDINGS

The drug combination displayed synergy, enhanced QQ activity, and suppressed AHL production in PAO1. At sub-inhibitory concentrations, the drug combination suppressed the expression of genes regulating QS and pseudomonal virulence, thereby inhibiting the production of virulence factors in PAO1. The drug combination compromised all forms of pseudomonal motility, strongly inhibited biofilm formation, and successfully eradicated preformed biofilms. Based on these findings, it is concluded that GeN (alone) does not harbor any QQ properties, but enhances the QQ potential of α-T. Moreover, combinational treatment protected C. elegans from pseudomonal infection and improved survival rates by 73 % at 96 h.

SIGNIFICANCE

For the first time, the molecular mechanism responsible for the anti-QS activity of α-T was unraveled through a comprehensive investigation, thereby asserting its potential as an anti-virulent drug against P. aeruginosa.

Quorum sensing in human gut and food microbiomes: Significance and potential for therapeutic targeting

Human gut and food microbiomes interact during digestion. The outcome of these interactions influences the taxonomical composition and functional capacity of the resident human gut microbiome, with potential consequential impacts on health and disease. Microbe-microbe interactions between the resident and introduced microbiomes, which likely influence host colonisation, are orchestrated by environmental conditions, elements of the food matrix, host-associated factors as well as social cues from other microorganisms. Quorum sensing is one example of a social cue that allows bacterial communities to regulate genetic expression based on their respective population density and has emerged as an attractive target for therapeutic intervention. By interfering with bacterial quorum sensing, for instance, enzymatic degradation of signalling molecules (quorum quenching) or the application of quorum sensing inhibitory compounds, it may be possible to modulate the microbial composition of communities of interest without incurring negative effects associated with traditional antimicrobial approaches. In this review, we summarise and critically discuss the literature relating to quorum sensing from the perspective of the interactions between the food and human gut microbiome, providing a general overview of the current understanding of the prevalence and influence of quorum sensing in this context, and assessing the potential for therapeutic targeting of quorum sensing mechanisms.

Guaiacol augments quorum quenching potential of Ciprofloxacin against Pseudomonas aeruginosa

AIM

The present study aims to investigate the antimicrobial as well as antivirulence potential and the principle mechanism of action of guaiacol against Pseudomonas aeruginosa.

METHODS AND RESULTS

Quorum sensing inhibition and membrane disruption studies were performed to check effect of guaiacol on the virulence of P. aeruginosa. Production of various virulence factors and biofilm formation were studied at sub-MIC concentration of guaiacol alone (1/8 MIC) and in combination with ciprofloxacin (1/2 FIC). Guaiacol exhibited synergistic interactions with ciprofloxacin and further reduced production of all virulence factors and biofilm formation. Using crystal violet (CV) assay and quantification of exopolysaccharide we observed weak biofilm formation, together with reduced motilities at sub MIC which was further visualized by confocal laser microscopy and Field Emission Scanning Electron Microscopy (FESEM).The antibacterial activity of guaiacol against P. aeruginosa upon 2×MIC exposure coincided with enhanced membrane permeability leading to disruption and release of cellular material as quantified by CV uptake assay and Sodium dodecyl suphate-polyacrylamide gel electrophoresis (SDS-PAGE). The results demonstrated that sub MICs of guaiacol in combination with ciprofloxacin can act as a potent alternate compound for attenuation of quorum sensing in P. aeruginosa.

CONCLUSION

Study reports that guaiacol in combination with ciprofloxacin at 1/2 FIC significantly compromised the bacterial growth and motilities alongside inducing quorum quenching potential. This was accompanied by inhibition of biofilm which subsequently decreased EPS production at sub MIC concentration. Furthermore, guaiacol in combination displayed a severe detrimental effect on bacterial membrane disruption, thereby enhancing cellular material release.

SIGNIFICANCE AND IMPACT OF STUDY

For the first time, the potential of guaiacol in combination with ciprofloxacin in attenuation of virulence factors and biofilm formation in P. aeruginosa were described. Results corroborate on how plant bioactive in synergism with antibiotics can act as alternate treatment regime to tackle the menace of drug resistance.

A novel colorimetric sensor array for real-time and on-site monitoring of meat freshness

Food quality control is essential in industry and daily life. In this work, we developed a novel colorimetric sensor array composed of several pH-sensitive dyes for monitoring meat freshness. A color change in the sensor array was seen after exposure to volatile organic compounds (VOCs), and the images were captured for precise quantification of the VOCs. In conjunction with pattern recognition, meat freshness at different storage periods was readily discerned, revealing that the as-fabricated colorimetric sensor array possessed excellent discrimination ability. The linear range for quantitative analysis of volatiles related to meat spoilage was from 5 ppm to 100 ppm, with a limit of detection at the ppb level (S/N = 3). Furthermore, the testing results obtained by the sensor in assessing meat freshness were validated by a standard method for measuring the total volatile basic nitrogen (TVB-N). The sensing signals showed good agreement with the results obtained in TVB-N when measuring real food samples. The sensor also displayed good reproducibility (RSD < 5%) and long-term stability. The sensor was successfully used for on-site and real-time determination of volatiles emitted from rotting meat, demonstrating its potential application in monitoring the quality and safety of meat products.

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

The quorum sensing (QS) circuitry of Pseudomonas aeruginosa represents an attractive target to attenuate bacterial virulence and antibiotic resistance. In this context, phytochemicals harboring anti-virulent properties have emerged as an alternative medicine to combat pseudomonal infections. Hence, this study was undertaken to investigate the synergistic effects and quorum quenching (QQ) potential of cinnamaldehyde (CiNN) in combination with gentamicin (GeN) against P. aeruginosa. The QQ activity of this novel combination was evaluated using a QS reporter strain and synergism was studied using chequerboard assays. Further, the genotypic and phenotypic expression of pseudomonal virulence factors was examined alongside biofilm formation. The combination of CiNN and GeN exhibited synergy and promising anti-QS activity. This drug combination was shown to suppress AHL production and downregulate the expression of critical QS genes in P. aeruginosa PAO1. Molecular docking revealed strong interactions between the QS receptors and CiNN, asserting its QQ potential. Bacterial motility was compromised along with a significant reduction in pyocyanin (72.3%), alginate (58.7%), rhamnolipid (33.6%), hemolysin (82.6%), protease (70.9%), and elastase (63.9%) production. The drug combination successfully eradicated preformed biofilms and inhibited biofilm formation by abrogating EPS production. Our findings suggest that although GeN alone could not attenuate QS, but was able to augment the anti-QS potential of CiNN. To validate our results using an infection model, we quantified the survival rates of Caenorhabditis elegans following PAO1 challenge. The combination significantly rescued C. elegans from PAO1 infection and improved its survival rate by 54% at 96 h. In summary, this study is the first to elucidate the mechanism behind the QQ prospects of CiNN (augmented in presence of GeN) by abrogating AHL production and increasing the survival rate of C. elegans, thereby highlighting its anti-virulent properties.

Application of Biotechnology in Specific Spoilage Organisms of Aquatic Products

Aquatic products are delicious and have high nutritive value, however, they are highly perishable during storage due to the growth and metabolism of microorganisms. The spoilage process of aquatic products was demonstrated to be highly related to the composition of microorganisms, in which the specific spoilage organisms (SSOs) are the main factors. In this article, the spoilage indicators of SSOs were systematically described, which could make a comprehensive evaluation of the quality of aquatic products. Quorum sensing (QS) regulates the growth, metabolism and characteristics of SSOs, the common signaling molecules and the QS system in the major SSOs of aquatic products were discussed. Moreover, we compared various technologies for the analysis of SSOs in aquatic products. Besides, quality control techniques based on microbiota regulating of aquatic products, including physical, chemical and biological preservation strategies, were also compared. In conclusion, novel preservation technologies and hurdle techniques are expected to achieve comprehensive inhibition of SSOs.

Screening and validation of quorum quenching enzyme PF2571 from Pseudomonas fluorescens strain PF08 to inhibit the spoilage of red sea bream filets

Bacteria are the main cause of spoilage for fish and fishery products. Through the inactivation of the quorum sensing (QS) system, quorum quenching (QQ) enzymes can block the synthesis of bacterial virulence factors and effectively inhibit bacteria-induced food spoilage. This study analyzed the changes of microbiota in red sea bream filets during refrigerated storage. The results showed a decrease in microbial diversity with storage time, with Aeromonas veronii becoming the dominant bacteria on day 4. A novel N-acyl homoserine lactones (AHL) acylase PF2571, from the screened QQ bacterium Pseudomonas fluorescens PF08, was identified and expressed in Escherichia coli to evaluate its QQ efficiency and effects on spoilage potential. Spoilage-related QS factors of A. veronii BY-8, including biofilm formation, motility, and protease, lipase, and alginate production, were inhibited by PF2571. Its inhibitory effect on red sea bream spoilage was demonstrated by the lower freshness indicators for PF2571 treated filets. Our study demonstrates the potential of the QQ enzyme for prolonging the shelf life of fish and fishery products.

Nemonoxacin enhances antibacterial activity and anti-resistant mutation ability of vancomycin against methicillin-resistant Staphylococcus aureus in an in vitro dynamic pharmacokinetic/pharmacodynamic model

Reduced susceptibility and emergence of resistance to vancomycin in methicillin-resistant Staphylococcus aureus (MRSA) have led to the development of various vancomycin based combinations. Nemonoxacin is a novel nonfluorinated quinolone with antibacterial activity against MRSA. The present study aimed to investigate the effects of nemonoxacin on antibacterial activity and the anti-resistant mutation ability of vancomycin for MRSA and explore whether quinolone resistance genes are associated with a reduction in the vancomycin minimal inhibitory concentration (MIC) and mutant prevention concentration (MPC) when combined with nemonoxacin. Four isolates, all with a vancomycin MIC of 2 μg/mL, were used in a modified in vitro dynamic pharmacokinetic/pharmacodynamic model to investigate the effects of nemonoxacin on antibacterial activity (M04, M23 and M24) and anti-resistant mutation ability (M04, M23 and M25, all with MPC ≥19.2 μg/mL) of vancomycin. The mutation sites of gyrA, gyrB, parC, and parE of 55 clinical MRSA isolates were sequenced. We observed that in M04 and M23, the combination of vancomycin (1g q12h) and nemonoxacin (0.5g qd) showed a synergistic bactericidal activity and resistance enrichment suppression. All clinical isolates resistant to nemonoxacin harbored gyrA (S84→L) mutation; gyrA (S84→L) and parC (E84→K) mutations were the two independent risk factors for the unchanged vancomycin MPC in combination. Nemonoxacin enhances the bactericidal activity and suppresses resistance enrichment ability of vancomycin against MRSA with a MIC of 2 μg/mL. Our in vitro data support the combination of nemonoxacin and vancomycin for the treatment of MRSA infection with a high MIC.

Bacillus spp. Inhibit Edwardsiella tarda Quorum-Sensing and Fish Infection

The disruption of pathogen communication or quorum-sensing (QS) via quorum-quenching (QQ) molecules has been proposed as a promising strategy to fight bacterial infections. Bacillus spp. have recognizable biotechnology applications, namely as probiotic health-promoting agents or as a source of natural antimicrobial molecules, including QQ molecules. This study characterized the QQ potential of 200 Bacillus spp., isolated from the gut of different aquaculture fish species, to suppress fish pathogens QS. Approximately 12% of the tested Bacillus spp. fish isolates (FI). were able to interfere with synthetic QS molecules. Ten isolates were further selected as producers of extracellular QQ-molecules and their QQ capacity was evaluated against the QS of important aquaculture bacterial pathogens, namely Aeromonas spp., Vibrio spp., Photobacterium damselae, Edwardsiela tarda, and Shigella sonnei. The results revealed that A. veronii and E. tarda produce QS molecules that are detectable by the Chr. violaceum biosensor, and which were degraded when exposed to the extracellular extracts of three FI isolates. Moreover, the same isolates, identified as B. subtilis, B. vezelensis, and B. pumilus, significantly reduced the pathogenicity of E. tarda in zebrafish larvae, increasing its survival by 50%. Taken together, these results identified three Bacillus spp. capable of extracellularly quenching aquaculture pathogen communication, and thus become a promising source of bioactive molecules for use in the biocontrol of aquaculture bacterial diseases.

Detection of Quorum Sensing N-Acyl-Homoserine Lactone Molecules Produced by Different Resistant Klebsiella pneumoniae Isolates Recovered from Poultry and Different Environmental Niches

This study aimed to detect and identify the N-acyl-homoserine lactones molecules (AHLs) produced by different resistant Klebsiella pneumoniae isolates recovered from poultry and environmental samples using a modified validated high-performance liquid chromatography method. A total of 56 K. pneumoniae isolates were recovered, investigated for their antibiotic susceptibility, and screened for AHLs production using the Agrobacterium tumefaciens NTL4 biosensor system and a validated high-performance liquid chromatography method. The results revealed the detection of different short- and long-chain AHLs molecules among 39 K. pneumoniae isolates recovered from poultry and environmental samples. All environmental isolates produced nine peaks with retention times for C4-HSL, C6-HSL, C12-HSL, C8-HSL, C14-HSL, C8-oxo-HSL, C10-HSL, C6-oxo-HSL, and C7-HSL. The most quantifiable AHL signal molecules in poultry isolates were C4-HSL, C6-HSL, and C12-HSL. No statistical correlation between the AHL-producing ability of K. pneumoniae isolates and antibiotic resistance was reported. To the best of our knowledge, this study provides the first detailed report on the detection and identification of AHLs in K. pneumoniae isolates recovered from poultry and environmental samples. Furthermore, it provides a new insight available tool other than LC-MS/MS for detection and identification of AHL molecules.

N-acyl homoserine lactone molecules assisted quorum sensing: effects consequences and monitoring of bacteria talking in real life

Bacteria utilize small signal molecules to monitor population densities. Bacteria arrange gene regulation in a method called Quorum Sensing (QS). The most widespread signalling molecules are N-Acyl Homoserine Lactones (AHLs/HSLs) for Gram-negative bacteria communities. QS plays significant role in the organizing of the bacterial gene that adapts to harsh environmental conditions for bacteria. It is involved in the arrangement of duties, such as biofilm formation occurrence, virulence activity of bacteria, production of antibiotics, plasmid conjugal transfer incident, pigmentation phenomenon and production of exopolysaccharide (EPS). QS obviously impacts on human health, agriculture and environment. AHL-related QS researches have been extensively studied and understood in depth for cell to cell intercommunication channel in Gram-negative bacteria. It is understood that AHL-based QS research has been extensively studied for cell-to-cell communication in Gram-negative bacteria; hence, a comprehensive study of AHLs, which are bacterial signal molecules, is required. The purpose of this review is to examine the effects of QS-mediated AHLs in many areas by looking at them from a different perspectives, such as clinic samples, food industry, aquatic life and wastewater treatment system.

An innovative role for luteolin as a natural quorum sensing inhibitor in Pseudomonas aeruginosa

AIMS

The emergence of antibiotic tolerance was a tricky problem in the treatment of chronic Pseudomonas aeruginosa-infected cystic fibrosis and burn victims. The quorum sensing (QS) inhibitor may serve as a new tactic for the bacterial resistance by inhibiting the biofilm formation and the production of virulence factors. This study explored the potential of luteolin as a QS inhibitor against P. aeruginosa and the molecular mechanism involved.

MAIN METHODS

Crystal violet staining, CLSM observation, and SEM analysis were carried out to assess the effect of luteolin on biofilm formation. The motility assays and the production of virulence factors were determined to evaluate the QS-inhibitory activity of luteolin. Acyl-homoserine lactone, RT-PCR, and molecular docking assays were conducted to explain its anti-QS mechanisms.

KEY FINDINGS

The biofilm formation, the production of virulence factors, and the motility of P. aeruginosa could be efficiently inhibited by luteolin. Luteolin could also attenuate the accumulation of the QS-signaling molecules N-(3-oxododecanoyl)-L-homoserine lactone (OdDHL) and N-butanoyl-L-homoserine lactone (BHL) (P < 0.01) and downregulate the transcription levels of QS genes (lasR, lasI, rhlR, and rhlI) (P < 0.01). Molecular docking analysis indicated that luteolin had a greater docking affinity with LasR regulator protein compared with OdDHL.

SIGNIFICANCE

This study is important as it reports the molecular mechanisms involved in the anti-biofilm formation activity of luteolin against P. aeruginosa. This study also indicated that luteolin could be helpful when used for the treatment of clinical drug-resistant infections of P. aeruginosa.

Aeromonas hydrophila RIT668 and Citrobacter portucalensis RIT669-Potential Zoonotic Pathogens Isolated from Spotted Turtles

Antimicrobial resistance (AMR) is one of the biggest challenges of the 21st century, and biofilm formation enables bacteria to resist antibiotic at much higher concentrations than planktonic cells. Earlier, we showed that the Gram-negative Aeromonas hydrophila RIT668 and Citrobacter portucalensis RIT669 (closely related to C. freundii NBRC 12681) from infected spotted turtles (Clemmys guttata), formed biofilms and upregulated toxin expression on plastic surfaces, and were predicted to possess multiple antibiotic resistance genes. Here, we show that they each resist several antibiotics in the planktonic phase, but were susceptible to neomycin, and high concentrations of tetracycline and cotrimoxazole. The susceptibility of their biofilms to neomycin and cotrimoxazole was tested using the Calgary device. For A. hydrophila, the minimum inhibitory concentration (MIC) = 500-1000, and the minimum biofilm eradication concentration (MBEC) > 1000 μg/mL, using cotrimoxazole, and MIC = 32.3-62.5, and MBEC > 1000 μg/mL, using neomycin. For C. freundii MIC = 7.8-15.6, and, MBEC > 1000 μg/mL, using cotrimoxazole, and MIC = 7.8, and MBEC > 1000 μg/mL, using neomycin. Both A. hydrophila and C. portucalensis activated an acyl homoserine lactone (AHL) dependent biosensor, suggesting that quorum sensing could mediate biofilm formation. Their multidrug resistance in the planktonic form, and weak biofilm eradication even with neomycin and cotrimoxazole, indicate that A. hydrophila and C. portucalensis are potential zoonotic pathogens, with risks for patients living with implants.