Identification of the natural product paeonol derived from peony bark as an inhibitor of the Salmonella enterica serovar Typhimurium type III secretion system

Battling Salmonella enteritidis infections: integrating proteomics and in vivo assessment of Galla Chinensis tannic acid

Salmonella infections pose a significant threat to animal and human health. Phytochemicals present a potential alternative treatment. Galla chinensis tannic acid (GCTA), a hydrolyzable polyphenolic compound, inhibits bacterial growth and demonstrates potential as an alternative or supplement to antibiotics to prevent Salmonella infections. However, little is known about the antimicrobial mechanism of GCTA against Salmonella. Here, we revealed 456 differentially expressed proteins upon GCTA treatment, impacting pathways related to DNA replication, repair, genomic stability, cell wall biogenesis, and lipid metabolism using TMT-labeled proteomic analysis. TEM analysis suggested altered bacterial morphology and structure post-treatment. A Salmonella-infected-mouse model indicated that GCTA administration improved inflammatory markers, alleviated intestinal histopathological alterations, and reduced Salmonella enterica serovar Enteritidis (S. Enteritidis) colonization in the liver and spleen of Salmonella-infected mice. The LD50 of GCTA was 4100 mg/kg with an oral single dose, vastly exceeding the therapeutic dose. Thus, GCTA exhibited antibacterial and anti-infective activity against S. Enteritidis. Our results provided insight into the molecular mechanisms of these antibacterial effects, and highlights the potential of GCTA as an alternative to antibiotics.

Acaricidal activities of paeonol from Moutan Cortex, dried bark of Paeonia × suffruticosa, against the grain pest mite Aleuroglyphus ovatus (Acari: Acaridae)

Aleuroglyphus ovatus (Acari: Acaridae) is a major pest mite of stored grains that is distributed worldwide. Paeonol, a phenolic component of the essential oil extracted from the Chinese herb Paeonia moutan, possesses a range of biological activities, including antiviral, antifungal and acaricidal activity. This study investigated the bioactivity of paeonol against A. ovatus and its effect on the activity of detoxification enzymes. The bioactivity of paeonol against A. ovatus was determined by contact, fumigation and repellency bioassays, and the mechanism was preliminarily explored via morphological observation of the color changes of mite epidermis and determination of the changing trend of some important enzymes associated with acaricidal efficacy in the mites. The results showed that the median lethal concentration (LC50) in the contact and fumigation bioassays was 9.832 μg/cm2 and 14.827 μg/cm3, respectively, and the acaricidal activity of paeonol was higher under direct contact than under fumigation. Dynamic symptomatology studies registered typical neurotoxicity symptoms including excitation, convulsion and paralysis in A. ovatus treated with paeonol. The enzyme activity of catalase (CAT), nitric oxide synthase (NOS) and glutathione-S-transferase (GST) was higher, whereas the activity of superoxide dismutase (SOD) and acetylcholinesterase (AChE) was lower, compared to the control group. CAT, NOS and GST were activated, whereas SOD and AChE activities were inhibited after paeonol intervention. Our findings suggest paeonol has potent acaricidal activity against A. ovatus and thus may be used as an agent to control the stored-product mite A. ovatus.

Synthesis of novel 5-amido-2-carboxypyrazines as inhibitors of the type three secretion system of Salmonella enterica serovar Typhimurium

A series of novel 5-amido-2-carboxypyrazine derivatives were designed, synthesized and evaluated for the inhibitory activities against the T3SS of Salmonella enterica serovar Typhimurium. Preliminary results displayed that the compounds 2f, 2g, 2h and 2i showed potent inhibitory activities against T3SS. Compound 2h was identified as the most potent T3SS inhibitor and the SPI-1 effector secretion was strongly inhibited by 2h in a dose-dependent manner. The effects of compound 2h on the SPI-1 genes transcription might be via impacting the SicA/InvF regulatory pathway.

Recent advances in the discovery of plant-derived antimicrobial natural products to combat antimicrobial resistant pathogens: insights from 2018-2022

Covering: 2018 to 2022Antimicrobial resistance (AMR) poses a significant global health threat. There is a rising demand for innovative drug scaffolds and new targets to combat multidrug-resistant bacteria. Before the advent of antibiotics, infections were treated with plants chosen from traditional medicine practices. Of Earth's 374 000 plant species, approximately 9% have been used medicinally, but most species remain to be investigated. This review illuminates discoveries of antimicrobial natural products from plants covering 2018 to 2022. It highlights plant-derived natural products with antibacterial, antivirulence, and antibiofilm activity documented in lab studies. Additionally, this review examines the development of novel derivatives from well-studied parent natural products, as natural product derivatives have often served as scaffolds for anti-infective agents.

Flos populi (Male Inflorescence of Populus tomentosa Carrière) Aqueous Extract Suppresses Salmonella Pullorum Infection by Affecting T3SS-1

Pullorum disease, caused by Salmonella Pullorum (S. Pullorum), is one of the most serious infectious diseases in the poultry industry. Flos populi is traditionally used in Eastern Asian countries to treat various intestinal diseases. However, the anti-infection mechanism of Flos populi is not very clear. In this study, we evaluated the anti-infective effects on S. Pullorum of Flos populi aqueous extract (FPAE) in chickens. FPAE significantly reduced S. Pullorum growth in vitro. At the cellular level, FPAE reduced S. Pullorum adhesion and invasion on DF-1 cells but did not affect its intracellular survival or replication in macrophages. Further investigation revealed that FPAE inhibited the transcription of T3SS-1 genes, which is the main virulence factor that mediates S. Pullorum adhesion and invasion in host cells. The results suggest that the anti-infective effect of FPAE likely occurs through the inhibition of S. Pullorum T3SS-1, thereby impairing its ability to adhere to and invade cells. Further, we evaluated its therapeutic effect on animal models (Jianghan domestic chickens) and found that FPAE reduced the bacterial loads in organs and decreased the mortality and weight loss of infected chickens. Our findings provide novel insights into the potential development of FPAE against S. Pullorum as an effective anti-virulence therapeutic substitute for antibiotics.

Targeting bacterial pathogenesis by inhibiting virulence-associated Type III and Type IV secretion systems

Infections caused by Gram-negative pathogens pose a major health burden. Both respiratory and gastrointestinal infections are commonly associated with these pathogens. With the increase in antimicrobial resistance (AMR) over the last decades, bacterial infections may soon become the threat they have been before the discovery of antibiotics. Many Gram-negative pathogens encode virulence-associated Type III and Type IV secretion systems, which they use to inject bacterial effector proteins across bacterial and host cell membranes into the host cell cytosol, where they subvert host cell functions in favor of bacterial replication and survival. These secretion systems are essential for the pathogens to cause disease, and secretion system mutants are commonly avirulent in infection models. Hence, these structures present attractive targets for anti-virulence therapies. Here, we review previously and recently identified inhibitors of virulence-associated bacterial secretions systems and discuss their potential as therapeutics.

Research Progress on Small Molecular Inhibitors of the Type 3 Secretion System

The overuse of antibiotics has led to severe bacterial drug resistance. Blocking pathogen virulence devices is a highly effective approach to combating bacterial resistance worldwide. Type three secretion systems (T3SSs) are significant virulence factors in Gram-negative pathogens. Inhibition of these systems can effectively weaken infection whilst having no significant effect on bacterial growth. Therefore, T3SS inhibitors may be a powerful weapon against resistance in Gram-negative bacteria, and there has been increasing interest in the research and development of T3SS inhibitors. This review outlines several reported small-molecule inhibitors of the T3SS, covering those of synthetic and natural origin, including their sources, structures, and mechanisms of action.

Cinnamaldehyde Resist Salmonella Typhimurium Adhesion by Inhibiting Type I Fimbriae

Salmonella Typhimurium (S. Typhimurium), a common foodborne pathogen, severely harms the public and food security. Type I fimbriae (T1F) of S. Typhimurium, plays a crucial role in the pathogenic processes; it mediates the adhesion of bacteria to the mannose receptor on the host cell, assists the bacteria to invade the host cell, and triggers an inflammatory response. Cinnamaldehyde is the main ingredient in cinnamon essential oil. In this study, cinnamaldehyde was demonstrated to inhibit the expression of T1F by hemagglutination inhibition test, transmission electron microscopy, and biofilms. The mechanism of cinnamaldehyde action was studied by proteomics technology, PCR and Western blotting. The results showed that cinnamaldehyde can inhibit T1F in S. typhimurium without the growth of bacteria, by regulating the level of expression and transcription of fimA, fimZ, fimY, fimH and fimW. Proteomics results showed that cinnamaldehyde downregulated the subunits and regulators of T1F. In addition, the invasion assays proved that cinnamaldehyde can indeed reduce the ability of S. typhimurium to adhere to cells. The results of animal experiments showed that the colonization in the intestinal tract and the expression levels of inflammatory cytokine were significantly decreased, and the intestinal mucosal immune factors MUC1 and MUC2 were increased under cinnamaldehyde treatment. Therefore, cinnamaldehyde may be a potential drug to target T1F to treat Salmonella infections.

Computational Identification of the Plausible Molecular Vaccine Candidates of Multidrug-Resistant Salmonella enterica

Salmonella enterica serovars are responsible for the life-threatening, fatal, invasive diseases that are common in children and young adults. According to the most recent estimates, globally, there are approximately 11–20 million cases of morbidity and between 128,000 and 161,000 mortality per year. The high incidence rates of diseases like typhoid, caused by the serovars Typhi and Paratyphi, and gastroenteritis, caused by the non-typhoidal Salmonellae, have become worse, with the ever-increasing pathogenic strains being resistant to fluoroquinolones or almost even the third generation cephalosporins, such as ciprofloxacin and ceftriaxone. With vaccination still being one of the chosen methods of eradicating this disease, identification of candidate proteins, to be utilized for effective molecular vaccines, has probably remained a challenging issue. In our study here, we portray the usage of computational tools to analyze and predict potential vaccine candidate(s) for the multi-drug resistant serovars of S. enterica.

The Herbal Compound Thymol Targets Multiple Salmonella Typhimurium Virulence Factors for Lon Protease Degradation

Many important bacterial pathogens are using the type III secretion system to deliver effectors into host cells. Salmonella Typhimurium (S. Typhimurium) is a pathogenic Gram-negative bacterium with the type III secretion system as its major virulence factor. Our previous studies demonstrated that thymol, a monoterpene phenol derivative of cymene, inhibited S. Typhimurium invasion into mammalian cells and protected mice from infection. However, the antibacterial mechanism of thymol is not clear. In this study, we revealed that thymol interferes with the abundance of about 100 bacterial proteins through proteomic analysis. Among the 42 proteins whose abundance was reduced, 11 were important virulence factors associated with T3SS-1. Further analyses with SipA revealed that thymol directly interacts with this protein to induce conformational changes, which makes it susceptible to the Lon protease. In agreement with this observation, thymol effectively blocks cell invasion by S. Typhimurium. Thus, thymol represents a class of anti-virulence compounds that function by targeting pathogenic factors for degradation.

Simultaneous Determination of the Five Constituents in Maiwei Dihuang Pills by the HPLC-DAD Method

OBJECTIVE

The purpose of study is to establish an HPLC-DAD method for determination of the five constituents (deoxyschizandrin, γ-schizandrin, loganin, paeoniflorin, and paeonol) in Maiwei Dihuang Pills.

METHODS

An Agilent ZORBAX SB-C18 chromatographic column was carried out to determine the five constituents of 50% methanol extract of Maiwei Dihuang Pills.

RESULTS

It was found the chromatographic peak resolution of each component in the study sample solution was 1.5 higher than that of other peaks and no peaks appeared in the blank control solution during the same time, suggesting specificity of HPLC-DAD was well established. The linearity test indicated that deoxyschizandrin, γ-schizandrin, loganin, paeoniflorin, and paeonol were 11.6-72.3 μg/mL, 6.4-45.2 μg/mL, 35.2-237.6 μg/mL, 18.1-114.2 μg/mL, and 32.2-215.3 μg/mL, respectively, suggesting each component has a good linear relationship within its own range. Additionally, the precision of HPLC-DAD was confirmed by a precision test; the stability of the study sample solution was confirmed by a stability test; and good reproducibility of HPLC-DAD was proved by a reproducible test. The recovery rate test showed that relative standard deviation (RSD) of recovery rate in deoxyschizandrin, γ-schizandrin, loganin, paeoniflorin, and paeonol was 100.26% (1.80%), 101.39% (1.74%), 101.19% (1.76%), 102.50% (1.65%), and 102.30% (1.58%), respectively.

CONCLUSIONS

HPLC-DAD used to determine the five constituents in Maiwei Dihuang Pills, and it was easier and faster to operate, showing good condition in repeatability, precision, stability, and recovery, which is a great option for quality control.

Paeonol Attenuates Quorum-Sensing Regulated Virulence and Biofilm Formation in Pseudomonas aeruginosa

With the prevalence of multidrug-resistant bacteria and clinical -acquired pathogenic infections, the development of quorum-sensing (QS) interfering agents is one of the most potential strategies to combat bacterial infections and antibiotic resistance. Chinese herbal medicines constitute a valuable bank of resources for the identification of QS inhibitors. Accordingly, in this research, some compounds were tested for QS inhibition using indicator strains. Paeonol is a phenolic compound, which can effectively reduce the production of violacein without affecting its growth in Chromobacterium violaceum ATCC 12472, indicating its excellent anti-QS activity. This study assessed the anti-biofilm activity of paeonol against Gram-negative pathogens and investigated the effect of paeonol on QS-regulated virulence factors in Pseudomonas aeruginosa. A Caenorhabditis elegans infection model was used to explore the anti-infection ability of paeonol in vivo. Paeonol exhibited an effective anti-biofilm activity against Gram-negative bacteria. The ability of paeonol to interfere with the AHL-mediated quorum sensing systems of P. aeruginosa was determined, found that it could attenuate biofilm formation, and synthesis of pyocyanin, protease, elastase, motility, and AHL signaling molecule in a concentration- and time-dependent manner. Moreover, paeonol could significantly downregulate the transcription level of the QS-related genes of P. aeruginosa including lasI/R, rhlI/R, pqs/mvfR, as well as mediated its virulence factors, lasA, lasB, rhlA, rhlC, phzA, phzM, phzH, and phzS. In vivo studies revealed that paeonol could reduce the pathogenicity of P. aeruginosa and enhance the survival rate of C. elegans, showing a moderate protective effect on C. elegans. Collectively, these findings suggest that paeonol attenuates bacterial virulence and infection of P. aeruginosa and that further research elucidating the anti-QS mechanism of this compound in vivo is warranted.

Type 3 secretion system 1 of Salmonella typhimurium and its inhibitors: a novel strategy to combat salmonellosis

Unsuccessful vaccination against Salmonella due to a large number of serovars, and antibiotic resistance, necessitates the development of novel therapeutics to treat salmonellosis. The development of anti-virulence agents against multi-drug-resistant bacteria is a novel strategy because of its non-bacterial feature. Hence, a thorough study of the type three secretion system (T3SS) of Salmonella would help us better understand its role in bacterial pathogenesis and development of anti-virulence agents. However, T3SS can be inhibited by different chemicals at different stages of infection and sequenced delivery of effectors can be blocked to restrict the progression of disease. This review highlights the role of T3SS-1 in the internalization, survival, and replication of Salmonella within the intestinal epithelium and T3SS inhibitors. We concluded that the better we understand the structures and functions of T3SS, the more we have chances to develop anti-virulence agents. Furthermore, greater insights into the T3SS inhibitors of Salmonella would help in the mitigation of the antibiotic resistance problem and would lead us to the era of new therapeutics against salmonellosis.

Developing Cyclic Peptomers as Broad-Spectrum Type III Secretion System Inhibitors in Gram-Negative Bacteria

Antibiotic-resistant bacteria are an emerging global health threat. New antimicrobials are urgently needed. The injectisome type III secretion system (T3SS), required by dozens of Gram-negative bacteria for virulence but largely absent from nonpathogenic bacteria, is an attractive antimicrobial target. We previously identified synthetic cyclic peptomers, inspired by the natural product phepropeptin D, that inhibit protein secretion through the Yersinia Ysc and Pseudomonas aeruginosa Psc T3SSs but do not inhibit bacterial growth. Here, we describe the identification of an isomer, 4EpDN, that is 2-fold more potent (50% inhibitory concentration [IC₅₀] of 4 μM) than its parental compound. Furthermore, 4EpDN inhibited the Yersinia Ysa and the Salmonella SPI-1 T3SSs, suggesting that this cyclic peptomer has broad efficacy against evolutionarily distant injectisome T3SSs. Indeed, 4EpDN strongly inhibited intracellular growth of Chlamydia trachomatis in HeLa cells, which requires the T3SS. 4EpDN did not inhibit the unrelated twin arginine translocation (Tat) system, nor did it impact T3SS gene transcription. Moreover, although the injectisome and flagellar T3SSs are evolutionarily and structurally related, the 4EpDN cyclic peptomer did not inhibit secretion of substrates through the Salmonella flagellar T3SS, indicating that cyclic peptomers broadly but specifically target the injectisome T3SS. 4EpDN reduced the number of T3SS needles detected on the surface of Yersinia pseudotuberculosis as detected by microscopy. Collectively, these data suggest that cyclic peptomers specifically inhibit the injectisome T3SS from a variety of Gram-negative bacteria, possibly by preventing complete T3SS assembly.

Myricetin inhibits the type III secretion system of Salmonella enterica serovar typhimurium by downregulating the Salmonella pathogenic island I gene regulatory pathway

Based on the in-depth study of type III secretion systems (T3SS) in pathogenic bacteria, approaches targeting T3SS have become new alternative strategies to combat drug-resistant bacterial infections. As an important food-borne pathogen, Salmonella enterica serovar Typhimurium (S. Typhimurium) injects effector proteins into host cells through the T3SS to disrupt cell signaling and host responses. In this study, myricetin was screened for its ability to block the translocation function of effector proteins (SipA/SipB) using cell biology and molecular biology methods. It exerted strong effects on inhibiting the expression of Salmonella pathogenicity island 1 (SPI-1)-associated effector proteins without affecting S. Typhimurium growth and thus prevented S. Typhimurium from invading HeLa cells and ultimately inhibited S. Typhimurium-mediated cell damage. In an animal experiment, myricetin comprehensively protected mice from death and pathological damage. A further analysis of the mechanism of action showed that myricetin interfered with the regulatory network of SPI-1-related genes, resulting in a significant decrease in the levels of key effector proteins, and thus inhibited T3SS-mediated virulence. In summary, this study provides a solution for clinical resistance to S. Typhimurium infection and potential candidate compounds. Myricetin, a potential T3SS inhibitor, possesses effective biological activity and exerts protective effects in vitro and in vivo. Myricetin will likely be developed as a novel type of antibiotic targeting S. Typhimurium infections in the future.

The in vitro and in vivo anti-virulence activities of Cinnamomum bejolghota by inhibiting type three secretion system effector proteins of Salmonella

The bark of Cinnamomum bejolghota (Buch.-Ham.) Sweet (C. bejolghota) is widely used as medicine to treat bacterial diarrhea in Myanmar. We previously reported that the bark extract of C. bejolghota significantly inhibited secretion effector proteins of the type three secretion system (T3SS) in Salmonella. This study is designed to investigate the anti-virulence potential of the C. bejolghota bark extract against Salmonella Typhimuriumin in in vivo and in vitro experiments. The results suggested that the polar fraction Fr.M₁ inhibited the secretion of effector proteins SipA, SipB, SipC and SipD without affecting bacteria growth and the translocation of SipC into MDA-MB-231 cells. In addition, Fr.M₁ alleviated inflammatory symptoms of mice in Salmonella-infected mouse model. Overall, the results provide evidence for medicinal usage of C. bejolghota bark to treat diarrhea in Myanmar.