Xylitol Inhibits Growth and Blocks Virulence in Serratia marcescens

A novel perspective on eugenol as a natural anti-quorum sensing molecule against Serratia sp

Serratia marcescens is commonly noted to be an opportunistic pathogen and is often associated with nosocomial infections. In addition to its high antibiotic resistance, it exhibits a wide range of virulence factors that confer pathogenicity. Targeting quorum sensing (QS) presents a potential therapeutic strategy for treating bacterial infections caused by S. marcescens, as it regulates the expression of various virulence factors. Inhibiting QS can effectively neutralize S. marcescens' bacterial virulence without exerting stress on bacterial growth, facilitating bacterial eradication by the immune system. In this study, the antibacterial and anti-virulence properties of eugenol against Serratia sp. were investigated. Eugenol exhibited inhibitory effects on the growth of Serratia, with a minimal inhibitory concentration (MIC) value of 16.15 mM. At sub-inhibitory concentrations, eugenol also demonstrated antiadhesive and eradication activities by inhibiting biofilm formation. Furthermore, it reduced prodigiosin production and completely inhibited protease production. Additionally, eugenol effectively decreased swimming and swarming motilities in Serratia sp. This study demonstrated through molecular modeling, docking and molecular dynamic that eugenol inhibited biofilm formation and virulence factor production in Serratia by binding to the SmaR receptor and blocking the formation of the HSL-SmaR complex. The binding of eugenol to SmaR modulates biofilm formation and virulence factor production by Serratia sp. These findings highlight the potential of eugenol as a promising agent to combat S. marcescens infections by targeting its virulence factors through quorum sensing inhibition.

Developing 3-(2-Isocyano-6-methylbenzyl)-1H-indole Derivatives to Enhance the Susceptibility of Serratia marcescens by Occluding Quorum Sensing

Quorum sensing (QS) inhibition is recognized as a novel antimicrobial target for infections caused by drug-resistant pathogens and is an attractive strategy for antipathogenic agent development. We designed and synthesized three parts of 3-(2-isocyanobenzyl)-1H-indole derivatives and tested their activity as novel quorum sensing inhibitors (QSIs). 3-(2-Isocyanobenzyl)-1H-indole derivatives demonstrated promising QS, biofilms, and prodigiosin inhibitory activities against Serratia marcescens at subminimum inhibitory concentrations (sub-MICs). In particular, 3-(2-isocyano-6-methylbenzyl)-1H-indole (IMBI, 32) was identified as the best candidate based on several screening assays, including biofilm and prodigiosin inhibition. Further studies demonstrated that exposure to IMBI at 1.56 μg/mL to S. marcescens NJ01 significantly inhibited the formation of biofilms by 42%. The IMBI treatment on S. marcescens NJ01 notably enhanced the susceptibility of the formed biofilms, destroying the architecture of the biofilms by up to 40%, as evidenced by scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). For interference of virulence factors in S. marcescens NJ01, IMBI at 3.12 μg/mL inhibited the activity of protease and extracellular polysaccharides (EPS) by 17% and 51%, respectively, which were higher than that of the positive control vanillic acid (VAN). Furthermore, IMBI downregulated the expression of QS- and biofilm-related genes fimA, bsmA, pigP, flhC, rssB, fimC, and rsmA by 1.02- to 2.74-fold. To confirm these findings, molecular docking was performed, which indicated that the binding of IMBI to SmaR, RhlI, RhlR, LasR, and CviR could antagonize the expression of QS-linked traits. In addition, molecular dynamic simulations (MD) and energy calculations indicated that the binding of receptors with IMBI was extremely stable. The biofilms of S. marcescens NJ01 were markedly reduced by 50% when IMBI (0.39 μg/mL) was combined with kanamycin (0.15 μg/mL). In conclusion, this study highlights the potency of IMBI in inhibiting the virulence factors of S. marcescens. IMBI has all the potential to be developed as an effective and efficient QS inhibitor and antibiofilm agent in order to restore or improve antimicrobial drug sensitivity.

Combating planktonic and biofilm growth of Serratia marcescens by repurposing ebselen

AIM OF THE STUDY

The rising instances of multidrug-resistant pathogens are rapidly evolving into a global healthcare crisis. Identifying new ways of synthesis of antibiotics is both time-consuming and expensive. Repurposing existing drugs for the treatment of such antimicrobial-resistant pathogens has also been explored.

METHODS AND RESULTS

In the current study, ebselen was screened for antibacterial and antibiofilm activity against Serratia marcescens. Various antibacterial studies such as minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), time-kill curves, intracellular reactive oxygen species (ROS) quantification, and colony-forming unit assays were performed. The antibiofilm potential was assayed by biofilm inhibition, cell surface hydrophobicity assay, eradication, quantification of extracellular DNA (eDNA), and extracellular polymeric substance (EPS) layer and scanning electron microscopy (SEM) analysis were performed. Anti-quorum sensing assay was validated by quantifying the virulence factors production. Further molecular docking of ebselen with two quorum sensing (QS) specific proteins was also carried out. Antibacterial susceptibility tests showed potent antimicrobial activity of ebselen against S. marcescens with MIC50 of 14 μg/mL. Ebselen's ability to disturb the redox environment by inducing significant ROS generation led to bacterial death. It also showed concentration-dependent bactericidal activity as indicated by reduced bacterial growth and colony-forming unit propagation. Ebselen was also found to prevent biofilm attachment by altering the cell surface hydrophobicity while also being effective against preformed biofilms as validated by scanning electron microscopy (SEM) analysis. Additionally, ebselen showed reduced virulence factors like urease enzyme activity and prodigiosin pigment production indicating its promising anti-quorum sensing potential. Molecular docking analysis validated the strong binding of ebselen with QS-specific proteins (1Joe and PigG) with binding energies of - 6.6 and - 8.1kj/mol through hydrogen bonds and aromatic interactions. These results show that ebselen has potent antibiofilm potential that can be explored to identify treatment against bacterial infections.

Transcriptome analysis reveals that yeast extract inhibits synthesis of prodigiosin by Serratia marcescens SDSPY-136

Prodigiosin (2-methyl-3-pentyl-6-methoxyprodiginine) is a valuable medicinal and edible natural pigment derived from Serratia marcescens. How prodigiosin synthesis is suppressed by environmental factors has not been investigated. Previous studies described a low level of prodigiosin production in the presence of yeast extracts. However, we have observed that S. marcescens SDSPY-136 did not synthesize prodigiosin in yeast extract culture. In this study, transcriptome sequencing of yeast extract cultures was used to estimate the metabolic control of the synthetic prodigiosin pathway in S. marcescens. Key phosphorylation enzymes in the glycolysis pathway, 6-phosphofructokinase, and glyceraldehyde 3-phosphate dehydrogenase, were downregulated by yeast extract and other carbon metabolism pathway genes were enhanced. Genes related to ribosomes, amino acid metabolism, and aminoacyl-tRNA biosynthesis were also highly up-regulated. The presence of metal ions in yeast extracts and the accumulation of fermentation metabolites alter the two-component signaling system, which regulated metabolism to various degrees. The results of metal ion testing suggested that prodigiosin inhibition could be caused by metal ions, such as zinc ion. The findings indicate that yeast extract may affect metabolism through multiple pathways in S. marcescens. This research sheds light on the mechanism of prodigiosin regulatory inhibition.

Relocating Glyceryl Trinitrate as an Anti-Virulence Agent against Pseudomonas aeruginosa and Serratia marcescens: Insights from Molecular and In Vivo Investigations

The problem of antibiotic resistance is a global critical public health concern. In light of the threat of returning to the pre-antibiotic era, new alternative approaches are required such as quorum-sensing (QS) disruption and virulence inhibition, both of which apply no discernible selective pressure on bacteria, therefore mitigating the potential for the development of resistant strains. Bearing in mind the significant role of QS in orchestrating bacterial virulence, disrupting QS becomes essential for effectively diminishing bacterial virulence. This study aimed to assess the potential use of sub-inhibitory concentration (0.25 mg/mL) of glyceryl trinitrate (GTN) to inhibit virulence in Serratia marcescens and Pseudomonas aeruginosa. GTN could decrease the expression of virulence genes in both tested bacteria in a significant manner. Histopathological study revealed the ability of GTN to alleviate the congestion in hepatic and renal tissues of infected mice and to reduce bacterial and leukocyte infiltration. This study recommends the use of topical GTN to treat topical infection caused by P. aeruginosa and S. marcescens in combination with antibiotics.

What’s old is new again: Insights into diabetic foot microbiome

Diabetes is a chronic disease that is considered one of the most stubborn global health problems that continues to defy the efforts of scientists and physicians. The prevalence of diabetes in the global population continues to grow to alarming levels year after year, causing an increase in the incidence of diabetes complications and health care costs all over the world. One major complication of diabetes is the high susceptibility to infections especially in the lower limbs due to the immunocompromised state of diabetic patients, which is considered a definitive factor in all cases. Diabetic foot infections continue to be one of the most common infections in diabetic patients that are associated with a high risk of serious complications such as bone infection, limb amputations, and life-threatening systemic infections. In this review, we discussed the circumstances associated with the high risk of infection in diabetic patients as well as some of the most commonly isolated pathogens from diabetic foot infections and the related virulence behavior. In addition, we shed light on the different treatment strategies that aim at eradicating the infection.

Inhibition of Listeria monocytogenes Cocktail Culture Biofilms on Crab and Shrimp Coupons and the Expression of Biofilm-Related Genes

Listeria monocytogenes, a bacterium that is transmitted by tainted food, causes the infection listeriosis. In this study, quercetin was tested for its antibacterial properties and effectiveness as a food additive in preventing the growth of L. monocytogenes cocktail (ATCC19117, ATCC19113, and ATCC15313) biofilms on crabs and shrimps. Quercetin showed the least bactericidal activity and no discernible microbial growth at a minimum inhibitory concentration (MIC) of 250 µg/mL. The biofilm inhibition was performed at sub-MICs (1/2, 1/4, and 1/8 MIC). There was no quercetin added to the control group. Additionally, the present work examines the expression of various genes related to biofilm formation and quorum sensing (flaA, fbp, agrA, hlyA, and prfA). The levels of target genes were all significantly down-regulated. Quercetin (0-125 µg/mL) on the surfaces of the crab and shrimp was studied; its inhibitory effects were measured as log reductions at 0.39-2.31 log CFU/cm² and 0.42-2.36 log CFU/cm², respectively (p < 0.05). Quercetin reduced the formation of biofilms by disrupting cell-to-cell connections and causing cell lysis, which led to the deformation of the cells, evidenced by FE-SEM (field-emission scanning electron microscopy). These findings emphasize the significance of using natural food agents to target bacteria throughout the entire food production process.

Diminishing the Pathogenesis of the Food-Borne Pathogen Serratia marcescens by Low Doses of Sodium Citrate

Protecting food from bacterial contamination is crucial for ensuring its safety and avoiding foodborne illness. Serratia marcescens is one of the food bacterial contaminants that can form biofilms and pigments that spoil the food product and could cause infections and illness to the consumer. Food preservation is essential to diminish such bacterial contaminants or at least reduce their pathogenesis; however, it should not affect food odor, taste, and consistency and must be safe. Sodium citrate is a well-known safe food additive and the current study aims to evaluate its anti-virulence and anti-biofilm activity at low concentrations against S. marcescens. The anti-virulence and antibiofilm activities of sodium citrate were evaluated phenotypically and genotypically. The results showed the significant effect of sodium citrate on decreasing the biofilm formation and other virulence factors, such as motility and the production of prodigiosin, protease, and hemolysins. This could be owed to its downregulating effect on the virulence-encoding genes. An in vivo investigation was conducted on mice and the histopathological examination of isolated tissues from the liver and kidney of mice confirmed the anti-virulence activity of sodium citrate. In addition, an in silico docking study was conducted to evaluate the sodium citrate binding ability to S. marcescens quorum sensing (QS) receptors that regulates its virulence. Sodium citrate showed a marked virtual ability to compete on QS proteins, which could explain sodium citrate’s anti-virulence effect. In conclusion, sodium citrate is a safe food additive and can be used at low concentrations to prevent contamination and biofilm formation by S. marcescens and other bacteria.

Biofilm Lifestyle in Recurrent Urinary Tract Infections

Urinary tract infections (UTIs) represent one of the most common infections that are frequently encountered in health care facilities. One of the main mechanisms used by bacteria that allows them to survive hostile environments is biofilm formation. Biofilms are closed bacterial communities that offer protection and safe hiding, allowing bacteria to evade host defenses and hide from the reach of antibiotics. Inside biofilm communities, bacteria show an increased rate of horizontal gene transfer and exchange of resistance and virulence genes. Additionally, bacterial communication within the biofilm allows them to orchestrate the expression of virulence genes, which further cements the infestation and increases the invasiveness of the infection. These facts stress the necessity of continuously updating our information and understanding of the etiology, pathogenesis, and eradication methods of this growing public health concern. This review seeks to understand the role of biofilm formation in recurrent urinary tact infections by outlining the mechanisms underlying biofilm formation in different uropathogens, in addition to shedding light on some biofilm eradication strategies.

Tryptone-stabilized silver nanoparticles' potential to mitigate planktonic and biofilm growth forms of Serratia marcescens

Several microbial pathogens are capable of forming biofilms. These microbial communities pose a serious challenge to the healthcare sector as they are quite difficult to combat. Given the challenges associated with the antibiotic-based management of biofilms, the research focus has now been shifted towards finding alternate treatment strategies that can replace or complement the antibacterial properties of antibiotics. The field of nanotechnology offers several novel and revolutionary approaches to eradicate biofilm-forming microbes. In this study, we evaluated the antibacterial and antibiofilm efficacy of in-house synthesized, tryptone-stabilized silver nanoparticles (Ts-AgNPs) against the superbug Serratia marcescens. The nanoparticles were of spherical morphology with an average hydrodynamic diameter of 170 nm and considerable colloidal stability with a Zeta potential of - 24 ± 6.15 mV. Ts-AgNPs showed strong antibacterial activities with a minimum inhibitory concentration (MIC₅₀) of 2.5 µg/mL and minimum bactericidal concentration (MBC) of 12.5 µg/mL against S. marcescens. The nanoparticles altered the cell surface hydrophobicity and inhibited biofilm formation. The Ts-AgNPs were also effective in distorting pre-existing biofilms by degrading the extracellular DNA (eDNA) component of the extracellular polymeric substance (EPS) layer. Furthermore, reduction in quorum-sensing (QS)-induced virulence factors produced by S. marcescens indicated that Ts-AgNPs attenuated the QS pathway. Together, these findings suggest that Ts-AgNPs are an important anti-planktonic and antibiofilm agent that can be explored for both the prevention and treatment of infections caused by S. marcescens.

Prevalence and Characterization of Serratia marcescens Isolated from Clinical Bovine Mastitis Cases in Ningxia Hui Autonomous Region of China

Purpose

This study aimed to investigate the prevalence and genetic characterization of Serratia marcescens isolates from clinical bovine mastitis in Ningxia Hui Autonomous Region of China.

Methods

S. marcescens was identified by the polymerase-chain reaction of 16S rRNA gene and sequencing. Antimicrobial susceptibility was tested by the disk diffusion method. Genes of resistance and virulence were determined by the PCR.

Results

Overall, S. marcescens were confirmed from 32 of 2897 (1.1%) mastitis milk samples. These isolates showed high resistance to cefazolin (30/32, 93.8%) and chloramphenicol (28/32, 87.5%). A 12.5% (4/32) of the isolates displayed multidrug resistance (MDR). The most prevalent resistant genes found in S. marcescens were TEM (32/32, 100%) and CTX-M (24/32, 75.0%; CTX-M-15, 14/32, 43.8%; CTX-M-14, 8/32, 25.0%; CTX-M-65, 2/32, 6.3%) for extended-spectrum beta-lactamase, cmlA (28/32, 87.5%) and floR (16/32, 50.0%) for chloramphenicol resistance, SIM-1 (2/32, 6.3%) for carbapenemases, and sdeB (28/32, 87.5%), sdeY (26/32, 81.3%), sdeR (26/32, 81.3%) and sdeD (20/32, 62.5%) for efflux pumps. Moreover, all isolates carried virulence genes flhD, entB, and kpn, and most of them contained mrkD (30/32, 93.8%), ycfM (26/32, 81.3%), bsmB (26/32, 81.3%), pigP (26/32, 81.3%), kfu (24/32, 75.0%) and shlB (24/32, 75.0%).

Conclusion

To our knowledge, this is the first report of genetic determinants for antimicrobial resistance and virulence in S. marcescens isolated from bovine mastitis cases in China. These findings are useful for developing strategies for prevention and treatment of bovine mastitis caused by S. marcescens in China.

Inhibitory effect of (E)-2-heptenal on Aspergillus flavus growth revealed by metabolomics and biochemical analyses

The prevention of fungal proliferation in postharvest grains is critical for maintaining grain quality and reducing mycotoxin contamination. Fumigation with natural gaseous fungicides is a promising and sustainable approach to protect grains from fungal spoilage. In this study, the antifungal activities of (E)-2-alkenals (C₅-C₁₀) on Aspergillus flavus were tested in the vapor phase, and (E)-2-heptenal showed the highest antifungal activity against A. flavus. (E)-2-Heptenal completely inhibited A. flavus growth at 0.0125 µL/mL and 0.2 µL/mL in the vapor phase and liquid contact, respectively. (E)-2-Heptenal can disrupt the plasma membrane integrity of A. flavus via leakage of intracellular electrolytes. Scanning electron microscopy indicated that the mycelial morphology of A. flavus was remarkably affected by (E)-2-heptenal. Metabolomic analyses indicated that 49 metabolites were significantly differentially expressed in A. flavus mycelia exposed to 0.2 µL/mL (E)-2-heptenal; these metabolites were mainly involved in galactose metabolism, starch and sucrose metabolism, the phosphotransferase system, and ATP-binding cassette transporters. ATP production was reduced in (E)-2-heptenal-treated A. flavus, and Janus Green B staining showed reduced cytochrome c oxidase activity. (E)-2-Heptenal treatment induced oxidative stress in A. flavus mycelia with an accumulation of superoxide anions and hydrogen peroxide and increased activities of superoxide dismutase and catalase. Simulated storage experiments showed that fumigation with 400 µL/L of (E)-2-heptenal vapor could completely inhibit A. flavus growth in wheat grains with 20% moisture; this demonstrates its potential use in preventing grain spoilage. This study provides valuable insights into understanding the antifungal effects of (E)-2-heptenal on A. flavus. KEY POINTS : • (E)-2-Heptenal vapor showed the highest antifungal activity against A. flavus among (C₅-C₁₀) (E)-2-alkenals. • The antifungal effects of (E)-2-heptenal against A. flavus were determined. • The antifungal actions of (E)-2-heptenal on A. flavus were revealed by metabolomics and biochemical analyses.

Hiring of the Anti-Quorum Sensing Activities of Hypoglycemic Agent Linagliptin to Alleviate the Pseudomonas aeruginosa Pathogenesis

Bacteria communicate with each other using quorum sensing (QS) which works in an inducer/receptor manner. QS plays the main role in orchestrating diverse bacterial virulence factors. Pseudomonas aeruginosa is one of the most clinically important bacterial pathogens that can cause infection in almost all body tissues. Besides its efficient capability to develop resistance to different antibiotics, P. aeruginosa acquires a huge arsenal of virulence factors that are controlled mainly by QS. Challenging QS with FDA-approved drugs and natural products was proposed as a promising approach to mitigate bacterial virulence enabling the host immunity to complete the eradication of bacterial infection. The present study aims to evaluate the dipeptidase inhibitor-4 inhibitor hypoglycemic linagliptin anti-QS and anti-virulence activities against P. aeruginosa in vitro, in vivo, and in silico. The current results revealed the significant ability to diminish the production of protease and pyocyanin, motility, and biofilm formation in P. aeruginosa. Furthermore, the histopathological examination of liver and kidney tissues of mice injected with linagliptin-treated bacteria showed an obvious reduction of pathogenesis. Linagliptin downregulation to QS-encoding genes, besides the virtual ability to interact with QS receptors, indicates its anti-QS activities. In conclusion, linagliptin is a promising anti-virulence and anti-QS candidate that can be used solely or in combination with traditional antimicrobial agents in the treatment of P. aeruginosa aggressive infections.

GC-MS Analysis and Microbiological Evaluation of Caraway Essential Oil as a Virulence Attenuating Agent against Pseudomonas aeruginosa

The emergence of resistant microbes threatens public health on our planet, and the emergence of resistant bacteria against the most commonly used antibiotics necessitates urgent alternative therapeutic options. One way to fight resistant microbes is to design new antimicrobial agents, however, this approach takes decades of research. An alternative or parallel approach is to target the virulence of bacteria with natural or synthetic agents. Active constituents from medicinal plants represent a wide library to screen for natural anti-virulence agents. Caraway is used as a traditional spice and in some medicinal applications such as carminative, antispasmodic, appetizer, and expectorant. Caraway essential oil is rich in terpenes that were previously reported to have antimicrobial activities. In our study, we tested the caraway essential oil in sub-inhibitory concentration as a virulence agent against the Gram-negative bacteria Pseudomonas aeruginosa. Caraway essential oil in sub-inhibitory concentration dramatically blocked protease activity, pyocyanin production, biofilm formation, and quorum sensing activity of P. aeruginosa. The gas chromatography-mass spectroscopy (GC-MS) profile of caraway fruit oil identified 13 compounds representing 85.4% of the total oil components with carvone and sylvestrene as the main constituents. In conclusion, caraway essential oil is a promising virulence-attenuating agent that can be used against topical infections caused by P. aeruginosa.

Formulation of water-soluble Buddleja globosa Hope extracts and characterization of their antimicrobial properties against Pseudomonas aeruginosa

Buddleja globosa Hope (BG) extracts are traditionally used to treat skin and gastric ulcers due to their healing properties. Non-aqueous solvents such as ethanol and DMSO are usually used to extract naturally occurring compounds. However, the cytotoxicity of these solvents and the low water solubility of the extracted compounds can hinder their biomedical applications. To overcome the limited solubility of the BG extracts, we aimed to enhance the solubility by processing a standardized hydroalcoholic extract (BG-126) through spray drying (SD), with and without two solubility enhancers. Spray-dried BG (BG-SD) extracts and spray-dried BG extracts plus polyvinylpyrrolidone (BG-SD PVP) and Soluplus® (BG-SD SP) were developed starting from BG-126 (containing 53% ethanol). These four formulations were characterized by total phenolic content, water solubility at 25°C and 37°C, and antimicrobial properties against Pseudomonas aeruginosa. All the SD formulations presented a solubility that allowed them to reach maximum concentrations of 1,024 μg/ml catechin for BG-SD and 2,048 μg/ml catechin for BG-SD PVP and BG-SD SP for antimicrobial testing. BG-SD showed the highest antimicrobial potency with a minimum inhibitory concentration (MIC) of 512 μg/ml catechin, followed by BG-126 with a MIC of 1,024 μg/ml catechin and SP. BG-126 was also shown to inhibit biofilm formation, as well as the excipients PVP and SP. The spray-dried BG (BG-SD) extract represents a promising natural active component with enhanced antimicrobial properties against P. aeruginosa for further research and the development of novel phytopharmaceuticals.

Controlling of Bacterial Virulence: Evaluation of Anti-Virulence Activities of Prazosin against Salmonella enterica

Salmonella enterica is a Gram-negative orofecal transmitted pathogen that causes a wide diversity of local and systemic illnesses. Salmonella enterica utilizes several interplayed systems to regulate its invasion and pathogenesis: namely, quorum sensing (QS) and type three secretion system (T3SS). In addition, S. enterica could sense the adrenergic hormones in the surroundings that enhance its virulence. The current study aimed to evaluate the ability of α-adrenoreceptor antagonist prazosin to mitigate the virulence of S. enterica serovar Typhimurium. The prazosin effect on biofilm formation and the expression of sdiA, qseC, qseE, and T3SS-type II encoding genes was evaluated. Furthermore, the prazosin intracellular replication inside macrophage and anti-virulence activity was evaluated in vivo against S. typhimurium. The current finding showed a marked prazosin ability to compete on SdiA and QseC and downregulate their encoding genes. Prazosin significantly downregulated the virulence factors encoding genes and diminished the biofilm formation, intracellular replication inside macrophages, and in vivo protected mice. To sum up, prazosin showed significant inhibitory activities against QS, T3SS, and bacterial espionage, which documents its considered anti-virulence activities.

3-Phenylpropan-1-Amine Enhanced Susceptibility of Serratia marcescens to Ofloxacin by Occluding Quorum Sensing

Serratia marcescens (S. marcescens) is an environmental bacterium that causes infections with high morbidity and mortality. Notably, infections caused by multidrug-resistant S. marcescens have become a global public health issue. Therefore, the discovery of promising compounds to reduce the virulence of pathogens and restore antibiotic activity against multidrug-resistant bacteria is critical. Quorum sensing (QS) regulates virulence factors and biofilm formation of microorganisms to increase their pathogenicity and is, therefore, an important factor in the formation of multidrug resistance. In this study, we found that 3-phenylpropan-1-amine (3-PPA) inhibited S. marcescens NJ01 biofilm formation and virulence factors, including prodigiosin, protease, lipase, hemolysin, and swimming. The combination of 3-PPA (50.0 μg/mL) and ofloxacin (0.2 μg/mL) enhanced S. marcescens NJ01 sensitivity to ofloxacin. Based on crystalline violet staining, scanning electron microscopy (SEM), and confocal laser scanning microscopy (CLSM), 3-PPA (50.0 μg/mL) reduced S. marcescens NJ01 biofilm formation by 48%. Quantitative real-time PCR (qRT-PCR) showed that 3-PPA regulated the expression of virulence- and biofilm-related genes fimA, fimC, bsmB, pigP, flhC, flhD, and sodB. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) indicated that 3-PPA affected intracellular metabolites of S. marcescens NJ01, leading to reduce metabolic activity. These results suggested that 3-PPA inhibits the pathogenicity of S. marcescens NJ01 by occluding QS. Thus, 3-PPA is feasible as an ofloxacin adjuvant to overcome multidrug-resistant S. marcescens and improve the treatment of intractable infections. IMPORTANCE Multidrug-resistant bacteria have become a major threat to global public health, leading to increased morbidity, mortality, and health care costs. Bacterial virulence factors and biofilms, which are regulated by quorum sensing (QS), are the primary causes of multidrug resistance. In this study, 3-PPA reduced virulence factors and eliminated biofilm formation by inhibiting QS in S. marcescens NJ01 bacteria, without affecting bacterial growth, thus restoring sensitivity to ofloxacin. Thus, the discovery of compounds that can restore antibiotic activity against bacteria is a promising strategy to mitigate multidrug resistance in pathogens.

Muting Bacterial Communication: Evaluation of Prazosin Anti-Quorum Sensing Activities against Gram-Negative Bacteria Pseudomonas aeruginosa, Proteus mirabilis, and Serratia marcescens

Simple Summary

Bacterial infections are considered one of the main challenges to global health. Bacterial virulence is controlled by interplayed systems to regulate bacterial invasion and infection in host tissues. Quorum sensing (QS) plays a crucial role in regulating virulence factor production, thus could be considered as the bacterial communication system in the bacterial population. The current study aimed to assess the anti-QS and anti-virulence activities of α-adrenoreceptor prazosin against three virulent Gram-negative bacteria. It was demonstrated that prazosin significantly downregulates the expression of QS-encoding genes and shows considered ability to compete on QS proteins in tested strains. Prazosin can significantly diminish biofilm formation and production of virulent enzymes and mitigate the virulence factors of tested strains. However, more testing is required alongside pharmacological and toxicological studies to assure the potential clinical use of prazosin as an adjuvant anti-QS and anti-virulence agent.

Abstract

Quorum sensing (QS) controls the production of several bacterial virulence factors. There is accumulative evidence to support that targeting QS can ensure a significant diminishing of bacterial virulence. Lessening bacterial virulence has been approved as an efficient strategy to overcome the development of antimicrobial resistance. The current study aimed to assess the anti-QS and anti-virulence activities of α-adrenoreceptor prazosin against three virulent Gram-negative bacteria Pseudomonades aeruginosa, Proteus mirabilis, and Serratia marcescens. The evaluation of anti-QS was carried out on a series of in vitro experiments, while the anti-virulence activities of prazosin were tested in an in vivo animal model. The prazosin anti-QS activity was assessed on the production of QS-controlled Chromobacterium violaceum pigment violacein and the expression of QS-encoding genes in P. aeruginosa. In vitro tests were performed to evaluate the prazosin effects on biofilm formation and production of extracellular enzymes by P. aeruginosa, P. mirabilis, and S. marcescens. A protective assay was conducted to evaluate the in vivo anti-virulence activity of prazosin against P. aeruginosa, P. mirabilis, and S. marcescens. Moreover, precise in silico molecular docking was performed to test the prazosin affinity to different QS receptors. The results revealed that prazosin significantly decreased the production of violacein and the virulent enzymes, protease and hemolysins, in the tested strains. Prazosin significantly diminished biofilm formation in vitro and bacterial virulence in vivo. The prazosin anti-QS activity was proven by its downregulation of QS-encoding genes and its obvious binding affinity to QS receptors. In conclusion, prazosin could be considered an efficient anti-virulence agent to be used as an adjuvant to antibiotics, however, it requires further pharmacological evaluations prior to clinical application.

The Inhibitory Effect of Quercetin on Biofilm Formation of Listeria monocytogenes Mixed Culture and Repression of Virulence

Listeria monocytogenes is the species of foodborne pathogenic bacteria that causes the infection listeriosis. The food production chain employs various methods to control biofilms, although none are completely successful. This study evaluates the effectiveness of quercetin as a food additive in reducing L. monocytogenes mixed cultures (ATCC19113, ATCC19117, and ATCC15313) biofilm formation on stainless steel (SS), silicon rubber (SR), and hand glove (HG) coupons, as well as tests its antimicrobial activities. With a minimum inhibitory concentration (MIC) of 250 µg/mL, the tested quercetin exhibited the lowest bactericidal action with no visible bacterial growth. In contrast, during various experiments in this work, the inhibitory efficacy of quercetin at sub-MICs levels (1/2, 1/4, and 1/8 MIC) against L. monocytogenes was examined. A control group was not added with quercetin. The current study also investigates the effect of quercetin on the expression of different genes engaged in motility (flaA, fbp), QS (agrA), and virulence (hlyA, prfA). Through increasing quercetin concentration, swarming and swimming motility, biofilm formation, and expression levels of target genes linked to flagella motility, virulence, and quorum-sensing were all dramatically reduced. Quercetin (0−125 μg/mL) was investigated on the SS, SR, and HG surfaces; the inhibitory effects were 0.39−2.07, 0.09−1.96 and 0.03−1.69 log CFU/cm2, respectively (p < 0.05). Field-emission scanning electron microscopy (FE-SEM) corroborated the findings because quercetin prevented the development of biofilms by severing cell-to-cell contacts and inducing cell lysis, which resulted in the loss of normal cell shape. Our findings suggest that plant-derived quercetin should be used as an antimicrobial agent in the food industry to control the development of L. monocytogenes biofilms. These outcomes suggest that bacterial targets are of interest for biofilm reduction, with alternative natural food agents in the food sector along the entire food production chain.

Amphotericin B-PEG Conjugates of ZnO Nanoparticles: Enhancement Antifungal Activity with Minimal Toxicity

Amphotericin B (AMB) is commonly used to treat life-threatening systemic fungal infections. AMB formulations that are more efficient and less nephrotoxic are currently unmet needs. In the current study, new ZnO-PEGylated AMB (ZnO-AMB-PEG) nanoparticles (NPs) were synthesized and their antifungal effects on the Candida spp. were investigated. The size and zeta potential values of AMB-PEG and ZnO-AMB-PEG NPs were 216.2 ± 26.9 to 662.3 ± 24.7 nm and −11.8 ± 2.02 to −14.2 ± 0.94 mV, respectively. The FTIR, XRD, and EDX spectra indicated that the PEG-enclosed AMB was capped by ZnO, and SEM images revealed the ZnO distribution on the surface NPs. In comparison to ZnO-AMB NPs and free AMB against C.albicans and C.neoformans, ZnO-AMB-PEG NPs significantly reduced the MIC and MFC. After a week of single and multiple dosage, the toxicity was investigated utilizing in vitro blood hemolysis, in vivo nephrotoxicity, and hepatic functions. ZnO-AMB-PEG significantly lowered WBC count and hematocrit concentrations when compared to AMB and ZnO-AMB. RBC count and hemoglobulin content, on the other hand, were unaltered. ZnO-AMB-PEG considerably lowered creatinine and blood urea nitrogen (BUN) levels when compared to AMB and ZnO-AMB. The difference in liver function indicators was determined to be minor by all formulae. These findings imply that ZnO-AMB-PEG could be utilized in the clinic with little nephrotoxicity, although more research is needed to determine the formulation’s in vivo efficacy.

Synthesis, Anticancer Potential and Comprehensive Toxicity Studies of Novel Brominated Derivatives of Bacterial Biopigment Prodigiosin from Serratia marcescens ATCC 27117

Prodigiosins (prodiginines) are a class of bacterial secondary metabolites with remarkable biological activities and color. In this study, optimized production, purification, and characterization of prodigiosin (PG) from easily accessible Serratia marcescens ATCC 27117 strain has been achieved to levels of 14 mg/L of culture within 24 h. Furthermore, environmentally friendly bromination of produced PG was used to afford both novel mono- and dibrominated derivatives of PG. PG and its Br derivatives showed anticancer potential with IC₅₀ values range 0.62–17.00 µg/mL for all tested cancer cell lines and induction of apoptosis but low selectivity against healthy cell lines. All compounds did not affect Caenorhabditiselegans at concentrations up to 50 µg/mL. However, an improved toxicity profile of Br derivatives in comparison to parent PG was observed in vivo using zebrafish (Danio rerio) model system, when 10 µg/mL applied at 6 h post fertilization caused death rate of 100%, 30% and 0% by PG, PG-Br, and PG-Br_2, respectively, which is a significant finding for further structural optimizations of bacterial prodigiosins. The drug-likeness of PG and its Br derivatives was examined, and the novel Br derivatives obey the Lipinski’s “rule of five”, with an exemption of being more lipophilic than PG, which still makes them good targets for further structural optimization.

Remedial Aspect of Zinc Oxide Nanoparticles Against Serratia Marcescens and Enterococcus Faecalis

Zinc oxide nanoparticles (ZnO NPs) have been widely used in biomedical applications due to their high biocompatibility and low toxicity to humans. The present work aimed to investigate the antibacterial effects of different concentrations of ZnO NPs on two opportunistic pathogens, Serratia marcescens and Enterococcus faecalis. The surface interaction between nanoparticles and bacterial cell wall, and the subsequent morphological alterations on the bacterial surface, were examined through Fourier transform infrared spectroscopy and scanning electron microscope. The energy dispersive X-ray analysis was used to confirm the elemental composition of ZnO NPs and the cellular accumulation of ZnO NPs in bacteria. The growth-inhibitory test demonstrated a dose-dependent growth inhibitory effect of ZnO NPs against both the test bacteria, as the higher concentration of nanoparticles caused the higher bacterial growth inhibition. The results showed that ZnO NPs caused a higher growth inhibition (63.50 ± 2.50%) on the Gram-positive bacterium E. faecalis compared to the Gram-negative bacterium S. marcescens (51.27 ± 4.56%). Fourier transform infrared spectrum revealed the possible involvement of hydroxyl, carboxyl, amides, methylene, and phosphate groups from the biomolecules of bacterial cell wall such as proteins, carbohydrates, lipids, and phospholipids in the interaction of ZnO NPs on bacterial cell surface. Energy dispersive X-ray analysis showed the higher accumulation of ZnO NPs in E. faecalis than S. marcescens analogous to the bacterial growth inhibition. Scanning electron microscopy images confirmed the antibacterial properties of ZnO NPs, showing the loss of integrity of cell membrane and distortion of bacterial cells. Hence, the potential of ZnO NP as an antibacterial agent against S. marcescens and E. faecalis has been confirmed.

Sodium Citrate Alleviates Virulence in Pseudomonas aeruginosa

The development of bacterial resistance is an insistent global health care issue, especially in light of the dwindled supply of new antimicrobial agents. This mandates the development of new innovative approaches to overcome the resistance development obstacle. Mitigation of bacterial virulence is an interesting approach that offers multiple advantages. Employing safe chemicals or drugs to mitigate bacterial virulence is an additive advantage. In the current study, the in vitro antivirulence activities of citrate were evaluated. Significantly, sodium citrate inhibited bacterial biofilm formation at sub-MIC concentrations. Furthermore, sodium citrate decreased the production of virulence factors protease and pyocyanin and diminished bacterial motility. Quorum sensing (QS) is the communicative system that bacterial cells utilize to communicate with each other and regulate the virulence of the host cells. In the present study, citrate in silico blocked the Pseudomonas QS receptors and downregulated the expression of QS-encoding genes. In conclusion, sodium citrate showed a significant ability to diminish bacterial virulence in vitro and interfered with QS; it could serve as a safe adjuvant to traditional antibiotic treatment for aggressive resistant bacterial infections such as Pseudomonas aeruginosa infections.

Anti-Quorum Sensing Activities of Gliptins against Pseudomonas aeruginosa and Staphylococcus aureus

The development of bacterial resistance to traditional antibiotics constitutes an emerging public health issue. Promising approaches have been innovated to conquer bacterial resistance, and targeting bacterial virulence is one of these approaches. Bacterial virulence mitigation offers several merits, as antivirulence agents do not affect the growth of bacteria and hence do not induce bacteria to develop resistance. In this direction, numerous drugs have been repurposed as antivirulence agents prior to their clinical use alone or in combination with traditional antibiotics. Quorum sensing (QS) plays a key role in controlling bacterial virulence. In the current study, dipeptidase inhibitor-4 (DPI-4) antidiabetic gliptins were screened for their antivirulence and anti-quorum sensing (anti-QS) activities against Gram-negative Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus. Upon assessing their antibiofilm activities, the ten tested gliptins significantly diminished biofilm formation. In particular, sitagliptin exhibited the most efficient antibiofilm activity, so it was chosen as a representative of all gliptins to further investigate its antivirulence activity. Sitagliptin significantly protected mice from P. aeruginosa and S. aureus pathogenesis. Furthermore, sitagliptin downregulated QS-encoding genes in P. aeruginosa and S. aureus. To test the anti-QS activities of gliptins, a detailed molecular docking study was conducted to evaluate the gliptins’ binding affinities to P. aeruginosa and S. aureus QS receptors, which helped explain the anti-QS activities of gliptins, particularly sitagliptin and omarigliptin. In conclusion, this study evaluates the possible antivirulence and anti-QS activities of gliptins that could be promising novel candidates for the treatment of aggressive Gram-negative or -positive bacterial infections either alone or as adjuvants to other antibiotics.

Anti-Quorum Sensing Activities of Gliptins against Pseudomonas aeruginosa and Staphylococcus aureus

The development of bacterial resistance to traditional antibiotics constitutes an emerging public health issue. Promising approaches have been innovated to conquer bacterial resistance, and targeting bacterial virulence is one of these approaches. Bacterial virulence mitigation offers several merits, as antivirulence agents do not affect the growth of bacteria and hence do not induce bacteria to develop resistance. In this direction, numerous drugs have been repurposed as antivirulence agents prior to their clinical use alone or in combination with traditional antibiotics. Quorum sensing (QS) plays a key role in controlling bacterial virulence. In the current study, dipeptidase inhibitor-4 (DPI-4) antidiabetic gliptins were screened for their antivirulence and anti-quorum sensing (anti-QS) activities against Gram-negative Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus. Upon assessing their antibiofilm activities, the ten tested gliptins significantly diminished biofilm formation. In particular, sitagliptin exhibited the most efficient antibiofilm activity, so it was chosen as a representative of all gliptins to further investigate its antivirulence activity. Sitagliptin significantly protected mice from P. aeruginosa and S. aureus pathogenesis. Furthermore, sitagliptin downregulated QS-encoding genes in P. aeruginosa and S. aureus. To test the anti-QS activities of gliptins, a detailed molecular docking study was conducted to evaluate the gliptins' binding affinities to P. aeruginosa and S. aureus QS receptors, which helped explain the anti-QS activities of gliptins, particularly sitagliptin and omarigliptin. In conclusion, this study evaluates the possible antivirulence and anti-QS activities of gliptins that could be promising novel candidates for the treatment of aggressive Gram-negative or -positive bacterial infections either alone or as adjuvants to other antibiotics.

Terazosin Interferes with Quorum Sensing and Type Three Secretion System and Diminishes the Bacterial Espionage to Mitigate the Salmonella Typhimurium Pathogenesis

Salmonella enterica is an invasive intracellular pathogen and hires diverse systems to manipulate its survival in the host cells. Salmonella could eavesdrop on the host cells, sensing and responding to the produced adrenergic hormones and other neurotransmitters, which results in the augmentation of its virulence and establishes its accommodation in host cells. The current study aims to assess the anti-virulence effect of α-adrenergic antagonist terazosin on S. Typhimurium. Our findings show that terazosin significantly reduced S. Typhimurium adhesion and biofilm formation. Furthermore, terazosin significantly decreased invasion and intracellular replication of S. Typhimurium. Interestingly, in vivo, terazosin protected the mice from S. Typhimurium pathogenesis. To understand the terazosin anti-virulence activity, its effect on quorum sensing (QS), bacterial espionage, and type three secretion system (T3SS) was studied. Strikingly, terazosin competed on the membranal sensors that sense adrenergic hormones and down-regulated their encoding genes, which indicates the ability of terazosin to diminish the bacterial eavesdropping on the host cells. Moreover, terazosin significantly reduced the Chromobacterium violaceum QS-controlled pigment production and interfered with the QS receptor Lux-homolog Salmonella SdiA, which indicates the possible terazosin-mediated anti-QS activity. Furthermore, terazosin down-regulated the expression of T3SS encoding genes. In conclusion, terazosin may mitigate S. Typhimurium virulence owing to its hindering QS and down-regulating T3SS encoding genes besides its inhibition of bacterial espionage.

Repurposing α-Adrenoreceptor Blockers as Promising Anti-Virulence Agents in Gram-Negative Bacteria

Antimicrobial resistance is among the world’s most urgent public health problems. Diminishing of the virulence of bacteria is a promising approach to decrease the development of bacterial resistance. Quorum sensing (QS) systems orchestrate the bacterial virulence in inducer–receptors manner. Bacteria can spy on the cells of the host by sensing adrenergic hormones and other neurotransmitters, and in turn, these neurotransmitters can induce bacterial pathogenesis. In this direction, α-adrenergic blockers were proposed as an anti-virulence agents through inhibiting the bacterial espionage. The current study aimed to explore the α-blockers’ anti-QS activities. Within comprehensive in silico investigation, the binding affinities of seven α-adrenoreceptor blockers were evaluated towards structurally different QS receptors. From the best docked α-blockers into QS receptors, terazosin was nominated to be subjected for further in vivo and in vitro anti-QS and anti-virulence activities against Chromobacterium violaceum and Pseudomonas aeruginosa. Terazosin showed a significant ability to diminish the QS-controlled pigment production in C. violaceum. Moreover, Terazosin decreased the P. aeruginosa biofilm formation and down-regulated its QS-encoding genes. Terazosin protected mice from the P. aeruginosa pathogenesis. In conclusion, α-adrenergic blockers are proposed as promising anti-virulence agents as they hinder QS receptors and inhibit bacterial espionage.

Synthesis, Antimicrobial, Anti-virulence and Anticancer Evaluation of New 5(4H)-Oxazolone-Based Sulfonamides

Since the synthesis of prontosil the first prodrug shares their chemical moiety, sulfonamides exhibit diverse modes of actions to serve as antimicrobials, diuretics, antidiabetics, and other clinical applications. This inspiring chemical nucleus has promoted several research groups to investigate the synthesis of new members exploring new clinical applications. In this study, a novel series of 5(4H)-oxazolone-based-sulfonamides (OBS) 9a–k were synthesized, and their antibacterial and antifungal activities were evaluated against a wide range of Gram-positive and -negative bacteria and fungi. Most of the tested compounds exhibited promising antibacterial activity against both Gram-positive and -negative bacteria particularly OBS 9b and 9f. Meanwhile, compound 9h showed the most potent antifungal activity. Moreover, the OBS 9a, 9b, and 9f that inhibited the bacterial growth at the lowest concentrations were subjected to further evaluation for their anti-virulence activities against Pseudomonas aeruginosa and Staphylococcus aureus. Interestingly, the three tested compounds reduced the biofilm formation and diminished the production of virulence factors in both P. aeruginosa and S. aureus. Bacteria use a signaling system, quorum sensing (QS), to regulate their virulence. In this context, in silico study has been conducted to assess the ability of OBS to compete with the QS receptors. The tested OBS showed marked ability to bind and hinder QS receptors, indicating that anti-virulence activities of OBS could be due to blocking QS, the system that controls the bacterial virulence. Furthermore, anticancer activity has been further performed for such derivatives. The OBS compounds showed variable anti-tumor activities, specifically 9a, 9b, 9f and 9k, against different cancer lines. Conclusively, the OBS compounds can serve as antimicrobials, anti-virulence and anti-tumor agents.

Computational and Biological Evaluation of β-Adrenoreceptor Blockers as Promising Bacterial Anti-Virulence Agents

Bacterial resistance to antibiotics is an increasing public health threat as it has the potential to affect people at any stage of life, as well as veterinary. Various approaches have been proposed to counteract the bacterial resistance development. Tackling bacterial virulence is one of the most promising approaches that confer several merits. The bacterial virulence is mainly regulated by a communication system known as quorum sensing (QS) system. Meanwhile, bacteria can sense the adrenergic hormones and eavesdrops on the host cells to establish their infection, adrenergic hormones were shown to enhance the bacterial virulence. In this study, β-adrenoreceptor blockers were proposed not only to stop bacterial espionage on our cells but also as inhibitors to the bacterial QS systems. In this context, a detailed in silico study has been conducted to evaluate the affinities of twenty-two β-blockers to compete on different structural QS receptors. Among the best docked and thermodynamically stable β-blockers; atenolol, esmolol, and metoprolol were subjected to further in vitro and in vivo investigation to evaluate their anti-QS activities against Chromobacterium violaceum, Pseudomonas aeruginosa and Salmonella typhimurium. The three tested β-blockers decreased the production of QS-controlled C. violaceum, and the formation of biofilm by P. aeruginosa and S. typhimurium. Additionally, the tested β-blockers down-regulated the P. aeruginosa QS-encoding genes and S. typhimurium sensor kinase encoding genes. Furthermore, metoprolol protected mice against P. aeruginosa and S. typhimurium. Conclusively, these investigated β-blockers are promising anti-virulence agents antagonizing adrenergic hormones induced virulence, preventing bacterial espionage, and blocking bacterial QS systems.

Alteration of Salmonella enterica Virulence and Host Pathogenesis through Targeting sdiA by Using the CRISPR-Cas9 System

Salmonella enterica is a common cause of many enteric infections worldwide and is successfully engineered to deliver heterologous antigens to be used as vaccines. Clustered Regularly Interspaced Short Palindromic Repeats (CRISPRs) RNA-guided Cas9 endonuclease is a promising genome editing tool. In the current study, a CRISPR-Cas9 system was used to target S.enterica sdiA that encodes signal molecule receptor SdiA and responds to the quorum sensing (QS) signaling compounds N-acylhomoserine lactones (AHLs). For this purpose, sdiA was targeted in both S.enterica wild type (WT) and the ΔssaV mutant strain, where SsaV has been reported to be an essential component of SPI2-T3SS. The impact of sdiA mutation on S. enterica virulence was evaluated at both early invasion and later intracellular replication in both the presence and absence of AHL. Additionally, the influence of sdiA mutation on the pathogenesis S. enterica WT and mutants was investigated in vivo, using mice infection model. Finally, the minimum inhibitory concentrations (MICs) of various antibiotics against S. enterica strains were determined. Present findings show that mutation in sdiA significantly affects S.enterica biofilm formation, cell adhesion and invasion. However, sdiA mutation did not affect bacterial intracellular survival. Moreover, in vivo bacterial pathogenesis was markedly lowered in S.enterica ΔsdiA in comparison with the wild-type strain. Significantly, double-mutant sdiA and ssaV attenuated the S. enterica virulence and in vivo pathogenesis. Moreover, mutations in selected genes increased Salmonella susceptibility to tested antibiotics, as revealed by determining the MICs and MBICs of these antibiotics. Altogether, current results clearly highlight the importance of the CRISPR-Cas9 system as a bacterial genome editing tool and the valuable role of SdiA in S.enterica virulence. The present findings extend the understanding of virulence regulation and host pathogenesis of Salmonellaenterica.

Anti-diabetics and antimicrobials: Harmony of mutual interplay

Diabetes is one of the four major non-communicable diseases, and appointed by the world health organization as the seventh leading cause of death worldwide. The scientists have turned over every rock in the corners of medical sciences in order to come up with better understanding and hence more effective treatments of diabetes. The continuous research on the subject has elucidated the role of immune disorders and inflammation as definitive factors in the trajectory of diabetes, assuring that blood glucose adjustments would result in a relief in the systemic stress leading to minimizing inflammation. On a parallel basis, microbial infections usually take advantage of immunity disorders and propagate creating a pro-inflammatory environment, all of which can be reversed by antimicrobial treatment. Standing at the crossroads between diabetes, immunity and infection, we aim in this review at projecting the interplay between immunity and diabetes, shedding the light on the overlapping playgrounds for the activity of some antimicrobial and anti-diabetic agents. Furthermore, we focused on the anti-diabetic drugs that can confer antimicrobial or anti-virulence activities.

A Novel Use of Allopurinol as A Quorum-Sensing Inhibitor in Pseudomonas aeruginosa

Pseudomonas aeruginosa can cause a variety of healthcare-associated infections by its arsenal of virulence factors. Virulence factor production is largely controlled by the cell-to-cell communication system termed quorum sensing (QS). Targeting QS may be a good approach to inhibit the production of virulence factors and attenuate pathogenicity without exerting selective stress on bacterial growth. This will greatly reduce the emergence of resistant mutants. In this work, we investigated the anti-virulence and anti-QS activities of the FDA-approved drug allopurinol against the P. aeruginosa PAO1 strain. Allopurinol at 200 µg/mL (1/10 MIC) significantly decreased the production of the QS-controlled Chromobacterium violaceum CV026 violet pigment violacein and other P. aeruginosa QS-controlled virulence factors phenotypically. Furthermore, allopurinol reduced the infiltration of P. aeruginosa and leucocytes and diminished the congestion in the liver and kidney tissues of infected mice. In silico study showed that allopurinol could compete with the autoinducers on binding to the receptors LasR and RhlR by hydrogen bonding. On the molecular level, qRT-PCR proved that allopurinol showed a significant downregulating effect on all tested QS-encoding genes that regulate virulence factor production. In summary, allopurinol is a promising QS inhibitor that may be useful in the future treatment of P. aeruginosa infection.

Secnidazole Is a Promising Imidazole Mitigator of Serratia marcescens Virulence

Serratia marcescens is an opportunistic pathogen that causes diverse nosocomial infections. S. marcescens has developed considerable resistance to different antibiotics and is equipped with an armory of virulence factors. These virulence factors are regulated in S. marcescens by an intercellular communication system termed quorum sensing (QS). Targeting bacterial virulence and QS is an interesting approach to mitigating bacterial pathogenesis and overcoming the development of resistance to antimicrobials. In this study, we aimed to evaluate the anti-virulence activities of secnidazole on a clinical isolate of S. marcescens. The effects of secnidazole at sub-inhibitory concentrations (sub-MICs) on virulence factors, swarming motility, biofilm formation, proteases, hemolysin activity, and prodigiosin production were evaluated in vitro. Secnidazole's protective activity against S. marcescens pathogenesis was assessed in vivo in mice. Furthermore, a molecular docking study was conducted to evaluate the binding ability of secnidazole to the S. marcescens SmaR QS receptor. Our findings showed that secnidazole at sub-MICs significantly reduced S. marcescens virulence factor production in vitro and diminished its pathogenesis in mice. The insilico docking study revealed a great ability of secnidazole to competitively hinder the binding of the autoinducer to the SmaR QS receptor. In conclusion, secnidazole is a promising anti-virulence agent that may be used to control infections caused by S. marcescens.

Not Only Antimicrobial: Metronidazole Mitigates the Virulence of Proteus mirabilis Isolated from Macerated Diabetic Foot Ulcer

Diabetic foot ulcers are recognized to be a severe complication of diabetes, increasing the risk of amputation and death. The bacterial infection of Diabetic foot ulcers with virulent and resistant bacteria as Proteus mirabilis greatly worsens the wound and may not be treated with conventional therapeutics. Developing new approaches to target bacterial virulence can be helpful to conquer such infections. In the current work, we evaluated the anti-virulence activities of the widely used antibacterial metronidazole. The minimum inhibitory concentrations (MIC) and minimum biofilm eradication concentrations (MEBC) were determined for selected antibiotics which P. mirabilis was resistant to them in the presence and absence of metronidazole in sub-MIC. The effect of metronidazole in sub-MIC on P. mirabilis virulence factors as production of exoenzymes, motilities, adhesion and biofilm formation, were evaluated. Furthermore, molecular docking of metronidazole into P. mirabilis adhesion and essential quorum sensing (QS) proteins, was performed. The results revealed a significant ability of metronidazole to in-vitro inhibit P. mirabilis virulence factors and antagonize its essential proteins. Moreover, metronidazole markedly decreased the MICs and MBECs of tested antibiotics. Conclusively, metronidazole in sub-MIC is a plausible anti-virulence and anti-QS agent that can be combined to other antibiotics as anti-virulence adjuvant to defeat aggressive infections.

Tackling Virulence of Pseudomonas aeruginosa by the Natural Furanone Sotolon

The bacterial resistance development due to the incessant administration of antibiotics has led to difficulty in their treatment. Natural adjuvant compounds can be co-administered to hinder the pathogenesis of resistant bacteria. Sotolon is the prevailing aromatic compound that gives fenugreek its typical smell. In the current work, the anti-virulence activities of sotolon on Pseudomonas aeruginosa have been evaluated. P. aeruginosa has been treated with sotolon at sub-minimum inhibitory concentration (MIC), and production of biofilm and other virulence factors were assessed. Moreover, the anti-quorum sensing (QS) activity of sotolon was in-silico evaluated by evaluating the affinity of sotolon to bind to QS receptors, and the expression of QS genes was measured in the presence of sotolon sub-MIC. Furthermore, the sotolon in-vivo capability to protect mice against P. aeruginosa was assessed. Significantly, sotolon decreased the production of bacterial biofilm and virulence factors, the expression of QS genes, and protected mice from P. aeruginosa. Conclusively, the plant natural substance sotolon attenuated the pathogenicity of P. aeruginosa, locating it as a plausible potential therapeutic agent for the treatment of its infections. Sotolon can be used in the treatment of bacterial infections as an alternative or adjuvant to antibiotics to combat their high resistance to antibiotics.