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

Mitigation Potential of Herbal Extracts and Constituent Bioactive Compounds on Salmonella in Meat-Type Poultry

Herbal extracts have been widely evaluated in poultry production for their beneficial effects and potential substitute for antibiotics, which contribute to AMR and risks to human health through the consumption of infected meat. Salmonellosis is a systemic infection caused by Salmonella, an intracellular bacterium with the ability to cause systemic infections with significant implications for both the health and safety of farmers and consumers. The excessive use of antibiotics has escalated the incidence of antibiotic resistance bacteria in the poultry and livestock industry, highlighting the urgent need for alternatives especially in meat-type poultry. Both in vivo usage and in vitro studies of bioactive compounds from herbal extracts have demonstrated the effective antimicrobial activities against pathogenic bacteria, showing promise in managing Salmonella infections and enhancing poultry performance. Phytobiotic feed additives have shown promising results in improving poultry output due to their pharmacological properties, such as stimulating consumption, and enhancing antioxidant properties and preventing the increasing antimicrobial resistance threats. Despite potential for synergistic effects from plant-derived compounds, a further investigation into is essential to fully understand their role and mechanisms of action, for developing effective delivery systems, and for assessing environmental sustainability in controlling Salmonella in poultry production.

Inhibitory effect of resveratrol on swimming motility and adhesion ability against Salmonella enterica serovar Typhimurium infection

Salmonella enterica serovar Typhimurium (S. typhimurium) is a common Gram-negative foodborne pathogen that threatens public health and hinders the development of livestock industry. Resveratrol, an important component in grape fruits and seeds, has been shown to possess multiple biological activities, but its potential effects on S. typhimurium-mediated virulence have been rarely reported. In this study, we investigated the effect of resveratrol on S. typhimurium flagella -mediated virulence. The results showed that resveratrol significantly reduced the transcription of flagella genes and swimming motility of S. typhimurium, and also inhibited the transcription of T3SS-related virulence genes with varying degrees inhibiting bacterial growth. Simultaneously, resveratrol significantly reduced the adhesion of S. typhimurium to HeLa cells. Unfortunately, resveratrol does not improve the survival rate of S. typhimurium-infected mice, but it reduces the bacterial load in the liver and spleen of infected mice, and it also has a certain degree of anti-inflammatory activity. In summary, these results indicated that resveratrol has the potential to be developed as an alternative drug or antibacterial agent to prevent Salmonella infection.

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.

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.

Response of Salmonella enterica serovar Typhimurium to alginate oligosaccharides fermented with fecal inoculum: integrated transcriptomic and metabolomic analyses

Alginate oligosaccharides (AOS), extracted from marine brown algae, are a common functional feed additive; however, it remains unclear whether they modulate the gut microbiota and microbial metabolites. The response of Salmonella enterica serovar Typhimurium, a common poultry pathogen, to AOS fermented with chicken fecal inocula was investigated using metabolomic and transcriptomic analyses. Single-strain cultivation tests showed that AOS did not directly inhibit the growth of S. Typhimurium. However, when AOS were fermented by chicken fecal microbiota, the supernatant of fermented AOS (F-AOS) exhibited remarkable antibacterial activity against S. Typhimurium, decreasing the abundance ratio of S. Typhimurium in the fecal microbiota from 18.94 to 2.94%. Transcriptomic analyses showed that the 855 differentially expressed genes induced by F-AOS were mainly enriched in porphyrin and chlorophyll metabolism, oxidative phosphorylation, and Salmonella infection-related pathways. RT-qPCR confirmed that F-AOS downregulated key genes involved in flagellar assembly and the type III secretory system of S. Typhimurium, indicating metabolites in F-AOS can influence the growth and metabolism of S. Typhimurium. Metabolomic analyses showed that 205 microbial metabolites were significantly altered in F-AOS. Among them, the increase in indolelactic acid and 3-indolepropionic acid levels were further confirmed using HPLC. This study provides a new perspective for the application of AOS as a feed additive against pathogenic intestinal bacteria.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-023-00176-z.

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.

New tools to mitigate drug resistance in Enterobacteriaceae - Escherichia coli and Klebsiella pneumoniae

Treatment to common bacterial infections are becoming ineffective of late, owing to the emergence and dissemination of antibiotic resistance globally. Escherichia coli and Klebsiella pneumoniae are the most notorious microorganisms and are among the critical priority pathogens listed by WHO in 2017. These pathogens are the predominant cause of sepsis, urinary tract infections (UTIs), pneumonia, meningitis and pyogenic liver abscess. Concern arises due to the resistance of bacteria to most of the beta lactam antibiotics like penicillin, cephalosporin, monobactams and carbapenems, even to the last resort antibiotics like colistin. Preventing influx by modulation of porins, extruding the antibiotics by overexpression of efflux pumps, mutations of drug targets/receptors, biofilm formation, altering the drug molecules and rendering them ineffective are few resistance mechanisms that are adapted by Enterobacteriaeceae upon exposure to antibiotics. The situation is exacerbated due to the process of horizontal gene transfer (HGT), wherein the genes encoding resistance mechanisms are transferred to the neighbouring bacteria through plasmids/phages/uptake of free DNA. Carbapenemases, other beta lactamases and mcr genes coding for colistin resistance are widely disseminated leading to limited/no therapeutic options against those infections. Development of new antibiotics can be viewed as a possible solution but it involves major investment, time and labour despite which, the bacteria can easily adapt to the new antibiotic and evolve resistance in a relatively short time. Targeting the resistance mechanisms can be one feasible alternative to tackle these multidrug resistant (MDR) pathogens. Removal of plasmid (plasmid curing) causing resistance, use of bacteriophages and bacteriotherapy can be other potential approaches to combat infections caused by MDR E. coli and K. pneumoniae. The present review discusses the efficacies of these therapies in mitigating these infections, which can be potentially used as an adjuvant therapy along with existing antibiotics.

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 as an Antivirulence Compound Interfering with a Morphological Transformation into Coccoid Forms and Potentiating Activity of Antibiotics against Helicobacter pylori

Helicobacter pylori, a gastric pathogen associated with a broad range of stomach diseases, has a high tendency to become resistant to antibiotics. One of the most important factors related to therapeutic failures is its ability to change from a spiral to a coccoid form. Therefore, the main aim of our original article was to determine the influence of myricetin, a natural compound with an antivirulence action, on the morphological transformation of H. pylori and check the potential of myricetin to increase the activity of antibiotics against this pathogen. We observed that sub-minimal inhibitory concentrations (sub-MICs) of this compound have the ability to slow down the process of transformation into coccoid forms and reduce biofilm formation of this bacterium. Using checkerboard assays, we noticed that the exposure of H. pylori to sub-MICs of myricetin enabled a 4–16-fold reduction in MICs of all classically used antibiotics (amoxicillin, clarithromycin, tetracycline, metronidazole, and levofloxacin). Additionally, RT-qPCR studies of genes related to the H. pylori morphogenesis showed a decrease in their expression during exposure to myricetin. This inhibitory effect was more strongly seen for genes involved in the muropeptide monomers shortening (csd3, csd6, csd4, and amiA), suggesting their significant participation in the spiral-to-coccoid transition. To our knowledge, this is the first research showing the ability of any compound to synergistically interact with all five antibiotics against H. pylori and the first one showing the capacity of a natural substance to interfere with the morphological transition of H. pylori from spiral to coccoid forms.