Tomatidine acts in synergy with aminoglycoside antibiotics against multiresistant Staphylococcus aureus and prevents virulence gene expression

Natural Products-Based Anticancer Agents: Synthesis and Anticancer Activities of Funtumine Amide/Sulfonamide Derivatives

Funtumine is a pregnene-type steroidal alkaloid exhibiting moderate anticancer activity. To discover novel natural product-based anticancer drugs, a series of novel funtumine amide/sulfonamide derivatives were papered and identified using spectroscopic techniques. Additionally, the structures of compounds 2j, 3a, and 4k were further confirmed through X-ray diffraction analysis. Biological activity experiments conducted against three cancer cell lines revealed that several of the synthesized compounds demonstrated inhibition activities comparable to or exceeding those of the commercial anticancer agent, 5-Fluorouracil. Especially compound 4i demonstrated a notably strong growth inhibitory effect on HePG2 (IC50=14.89 μM) and HCT116 (IC50=15.67 μM) cell lines, while exhibiting minimal cytotoxicity towards human normal BEAS-2B cells. Preliminary structure-activity relationships (SARs) analysis indicated that the conversion of the carbonyl group at the C-20 position of funtumine to a hydroxyl group could yield more potent compounds.

Plant-Derived Antimicrobials and Their Crucial Role in Combating Antimicrobial Resistance

Antibiotic resistance emerged shortly after the discovery of the first antibiotic and has remained a critical public health issue ever since. Managing antibiotic resistance in clinical settings continues to be challenging, particularly with the rise of superbugs, or bacteria resistant to multiple antibiotics, known as multidrug-resistant (MDR) bacteria. This rapid development of resistance has compelled researchers to continuously seek new antimicrobial agents to curb resistance, despite a shrinking pipeline of new drugs. Recently, the focus of antimicrobial discovery has shifted to plants, fungi, lichens, endophytes, and various marine sources, such as seaweeds, corals, and other microorganisms, due to their promising properties. For this review, an extensive search was conducted across multiple scientific databases, including PubMed, Elsevier, ResearchGate, Scopus, and Google Scholar, encompassing publications from 1929 to 2024. This review provides a concise overview of the mechanisms employed by bacteria to develop antibiotic resistance, followed by an in-depth exploration of plant secondary metabolites as a potential solution to MDR pathogens. In recent years, the interest in plant-based medicines has surged, driven by their advantageous properties. However, additional research is essential to fully understand the mechanisms of action and verify the safety of antimicrobial phytochemicals. Future prospects for enhancing the use of plant secondary metabolites in combating antibiotic-resistant pathogens will also be discussed.

Mode of Antibacterial Action of Tomatidine C3-Diastereoisomers

Tomatidine (TO) is a natural narrow-spectrum antibiotic acting on the Staphylococcus aureus small colony variant (SCV) with a minimal inhibitory concentration (MIC) of 0.06 µg/mL while it shows no activity against prototypical strains (MIC > 128 µg/mL). To expand the spectrum of activity of TO, the 3β-hydroxyl group was substituted with an ethane-1,2-diamine, resulting in two diastereoisomers, TM-02 (C3-β) and TM-03 (C3-α). These molecules are equally potent against prototypical S. aureus and E. coli strains (MIC 8 and 32 µg/mL, respectively), whereas TM-02 is more potent against SCV (MIC 0.5 µg/mL) and hyperpermeable E. coli strains (MIC 1 µg/mL). The differences in their modes of action were investigated. We used membrane vesicles to confirm the inhibition of the bacterial ATP synthase, the documented target of TO, and measured effects on bacterial cell membranes. Both molecules inhibited E. coli ATP synthase, with Ki values of 1.1 µM and 3.5 µM for TM-02 and TM-03, respectively, and the bactericidal effect of TM-02 was linked to ATP synthase inhibition. Furthermore, TM-02 had no major effect on the membrane fluidity and gradually reduced membrane potential. In contrast, TM-03 caused structural damages to membranes and completely disrupted the membrane potential (>90%). We were successful in broadening the spectrum of activity of TO. C3-β-diastereoisomers may have more specific antibacterial action than C3-α.

Interactions of naturally occurring compounds with antimicrobials

Antibiotics are among the most often used medications in human healthcare and agriculture. Overusing these substances can lead to complications such as increasing antibiotic resistance in bacteria or a toxic effect when administering large amounts. To solve these problems, new solutions in antibacterial therapy are needed. The use of natural products in medicine has been known for centuries. Some of them have antibacterial activity, hence the idea to combine their activity with commercial antibiotics to reduce the latter's use. This review presents collected information on natural compounds (terpenes, alkaloids, flavonoids, tannins, sulfoxides, and mycotoxins), of which various drug interactions have been observed. Many of the indicated compounds show synergistic or additive interactions with antibiotics, which suggests their potential for use in antibacterial therapy, reducing the toxicity of the antibiotics used and the risk of further development of bacterial resistance. Unfortunately, there are also compounds which interact antagonistically, potentially hindering the therapy of bacterial infection. Depending on its mechanism of action, each compound can behave differently in combination with different antibiotics and when acting against various bacterial strains.

AADB: A Manually Collected Database for Combinations of Antibiotics With Adjuvants

Antimicrobial resistance is a global public health concern. The lack of innovations in antibiotic development has led to renewed interest in antibiotic adjuvants. However, there is no database to collect antibiotic adjuvants. Herein, we build a comprehensive database named Antibiotic Adjuvant DataBase (AADB) by manually collecting relevant literature. Specifically, AADB includes 3,035 combinations of antibiotics with adjuvants, covering 83 antibiotics, 226 adjuvants, and 325 bacterial strains. AADB provides user-friendly interfaces for searching and downloading. Users can easily obtain these datasets for further analysis. In addition, we also collected related datasets (e.g., chemogenomic and metabolomic data) and proposed a computational strategy to dissect these datasets. As a test case, we identified 10 candidates for minocycline, and 6 of 10 candidates are the known adjuvants that synergize with minocycline to inhibit the growth of E. coli BW25113. We hope that AADB can help users to identify effective antibiotic adjuvants. AADB is freely available at http://www.acdb.plus/AADB.

Biofilm stimulating activity of solanidine and Solasodine in Pseudomonas aeruginosa

BACKGROUND

Biofilm formation has reported as an important virulence associated properties of Pseudomonas aeruginosa that is regulated by quorum-sensing associated genes. Biofilm and quorum-sensing interfering properties of steroidal alkaloids, Solanidine and Solasodine were investigated in the present study.

RESULTS

Biofilm formation capacity and relative expression level of five studied genes(lasI, lasR, rhlI, rhlR and algD) were significantly increased dose-dependently after treatment with sub-inhibitory concentrations (32 and 512 µg/ml) of the both Solanidine and Solasodine. Biofilm formation capacity was more stimulated in weak biofilm formers(9 iaolates) in comparison to the strong biofilm producers(11 isolates). The lasI gene was the most induced QS-associated gene among five investigated genes.

CONCLUSION

Biofilm inducing properties of the plants alkaloids and probably medicines derived from them has to be considered for revision of therapeutic guidelines. Investigating the biofilm stimulating properties of corticosteroids and other medicines that comes from plant alkaloids also strongly proposed.

The Therapeutic Value of Solanum Steroidal (Glyco)Alkaloids: A 10-Year Comprehensive Review

Steroidal (glycol)alkaloids S(G)As are secondary metabolites made of a nitrogen-containing steroidal skeleton linked to a (poly)saccharide, naturally occurring in the members of the Solanaceae and Liliaceae plant families. The genus Solanum is familiar to all of us as a food source (tomato, potato, eggplant), but a few populations have also made it part of their ethnobotany for their medicinal properties. The recent development of the isolation, purification and analysis techniques have shed light on the structural diversity among the SGAs family, thus attracting scientists to investigate their various pharmacological properties. This review aims to overview the recent literature (2012-2022) on the pharmacological benefits displayed by the SGAs family. Over 17 different potential therapeutic applications (antibiotic, antiviral, anti-inflammatory, etc.) were reported over the past ten years, and this unique review analyzes each pharmacological effect independently without discrimination of either the SGA's chemical identity or their sources. A strong emphasis is placed on the discovery of their biological targets and the subsequent cellular mechanisms, discussing in vitro to in vivo biological data. The therapeutic value and the challenges of the solanum steroidal glycoalkaloid family is debated to provide new insights for future research towards clinical development.

Staphylococcus aureus Small-Colony Variants from Airways of Adult Cystic Fibrosis Patients as Precursors of Adaptive Antibiotic-Resistant Mutations

Prototypic Staphylococcus aureus and their small-colony variants (SCVs) are predominant in cystic fibrosis (CF), but the interdependence of these phenotypes is poorly understood. We characterized S. aureus isolates from adult CF patients over several years. Of 18 S. aureus-positive patients (58%), 13 (72%) were positive for SCVs. Characterization included genotyping, SCCmec types, auxotrophy, biofilm production, antibiotic susceptibilities and tolerance, and resistance acquisition rates. Whole-genome sequencing revealed that several patients were colonized with prototypical and SCV-related clones. Some clonal pairs showed acquisition of aminoglycoside resistance that was not explained by aminoglycoside-modifying enzymes, suggesting a mutation-based process. The characteristics of SCVs that could play a role in resistance acquisition were thus investigated further. For instance, SCV isolates produced more biofilm (p < 0.05) and showed a higher survival rate upon exposure to ciprofloxacin and vancomycin compared to their prototypic associated clones. SCVs also developed spontaneous rifampicin resistance mutations at a higher frequency. Accordingly, a laboratory-derived SCV (ΔhemB) acquired resistance to ciprofloxacin and gentamicin faster than its parent counterpart after serial passages in the presence of sub-inhibitory concentrations of antibiotics. These results suggest a role for SCVs in the establishment of persistent antibiotic-resistant clones in adult CF patients.

Phytochemicals as Invaluable Sources of Potent Antimicrobial Agents to Combat Antibiotic Resistance

Plants have been used for therapeutic purposes against various human ailments for several centuries. Plant-derived natural compounds have been implemented in clinics against microbial diseases. Unfortunately, the emergence of antimicrobial resistance has significantly reduced the efficacy of existing standard antimicrobials. The World Health Organization (WHO) has declared antimicrobial resistance as one of the top 10 global public health threats facing humanity. Therefore, it is the need of the hour to discover new antimicrobial agents against drug-resistant pathogens. In the present article, we have discussed the importance of plant metabolites in the context of their medicinal applications and elaborated on their mechanism of antimicrobial action against human pathogens. The WHO has categorized some drug-resistant bacteria and fungi as critical and high priority based on the need to develope new drugs, and we have considered the plant metabolites that target these bacteria and fungi. We have also emphasized the role of phytochemicals that target deadly viruses such as COVID-19, Ebola, and dengue. Additionally, we have also elaborated on the synergetic effect of plant-derived compounds with standard antimicrobials against clinically important microbes. Overall, this article provides an overview of the importance of considering phytogenous compounds in the development of antimicrobial compounds as therapeutic agents against drug-resistant microbes.

Inhibitors of ATP Synthase as New Antibacterial Candidates

ATP, the power of all cellular functions, is constantly used and produced by cells. The enzyme called ATP synthase is the energy factory in all cells, which produces ATP by adding inorganic phosphate (Pi) to ADP. It is found in the inner, thylakoid and plasma membranes of mitochondria, chloroplasts and bacteria, respectively. Bacterial ATP synthases have been the subject of multiple studies for decades, since they can be genetically manipulated. With the emergence of antibiotic resistance, many combinations of antibiotics with other compounds that enhance the effect of these antibiotics have been proposed as approaches to limit the spread of antibiotic-resistant bacteria. ATP synthase inhibitors, such as resveratrol, venturicidin A, bedaquiline, tomatidine, piceatannol, oligomycin A and N,N-dicyclohexylcarbodiimide were the starting point of these combinations. However, each of these inhibitors target ATP synthase differently, and their co-administration with antibiotics increases the susceptibility of pathogenic bacteria. After a brief description of the structure and function of ATP synthase, we aim in this review to highlight therapeutic applications of the major bacterial ATP synthase inhibitors, including animal’s venoms, and to emphasize their importance in decreasing the activity of this enzyme and subsequently eradicating resistant bacteria as ATP synthase is their source of energy.

An Assessment of the In Vitro Models and Clinical Trials Related to the Antimicrobial Activities of Phytochemicals

An increased number antibiotic-resistant bacteria have emerged with the rise in antibiotic use worldwide. As such, there has been a growing interest in investigating novel antibiotics against antibiotic-resistant bacteria. Due to the extensive history of using plants for medicinal purposes, scientists and medical professionals have turned to plants as potential alternatives to common antibiotic treatments. Unlike other antibiotics in use, plant-based antibiotics have the innate ability to eliminate a broad spectrum of microorganisms through phytochemical defenses, including compounds such as alkaloids, organosulfur compounds, phenols, coumarins, and terpenes. In recent years, these antimicrobial compounds have been refined through extraction methods and tested against antibiotic-resistant strains of Gram-negative and Gram-positive bacteria. The results of the experiments demonstrated that plant extracts successfully inhibited bacteria independently or in combination with other antimicrobial products. In this review, we examine the use of plant-based antibiotics for their utilization against antibiotic-resistant bacterial infections. In addition, we examine recent clinical trials utilizing phytochemicals for the treatment of several microbial infections.

High-Throughput Transcriptomic Profiling Reveals the Inhibitory Effect of Hydroquinine on Virulence Factors in Pseudomonas aeruginosa

Hydroquinine is an organic alkaloid compound that exhibits antimicrobial activity against several bacterial strains including strains of both drug-sensitive and multidrug-resistant P. aeruginosa. Despite this, the effects of hydroquinine on virulence factors in P. aeruginosa have not yet been characterized. We therefore aimed to uncover the mechanism of P. aeruginosa hydroquinine-sensitivity using high-throughput transcriptomic analysis. We further confirmed whether hydroquinine inhibits specific virulence factors using RT-qPCR and phenotypic analysis. At half the minimum inhibitory concentration (MIC) of hydroquinine (1.250 mg/mL), 254 genes were differentially expressed (97 downregulated and 157 upregulated). We found that flagellar-related genes were downregulated by between −2.93 and −2.18 Log2-fold change. These genes were consistent with the analysis of gene ontology and KEGG pathway. Further validation by RT-qPCR showed that hydroquinine significantly suppressed expression of the flagellar-related genes. By analyzing cellular phenotypes, P. aeruginosa treated with ½MIC of hydroquinine exhibited inhibition of motility (30−54% reduction) and pyocyanin production (~25−27% reduction) and impaired biofilm formation (~57−87% reduction). These findings suggest that hydroquinine possesses anti-virulence factors, through diminishing flagellar, pyocyanin and biofilm formation.

In Vitro and In Vivo Bactericidal and Antibiofilm Efficacy of Alpha Mangostin Against Staphylococcus aureus Persister Cells

The formation of persister cells is associated with recalcitrance and infections. In this study, we examined the antimicrobial property of alpha mangostin, a natural xanthone molecule, against methicillin-resistant Staphylococcus aureus (MRSA) persisters and biofilm. The MIC of alpha mangostin against MRSA persisters was 2 µg/ml, and activity was mediated by causing membrane permeabilization within 30 min of exposure. The membrane activity of alpha mangostin was further studied by fast-killing kinetics of MRSA persiste r cells and found that the compound exhibited 99.99% bactericidal activity within 30 min. Furthermore, alpha mangostin disrupted established MRSA biofilms and inhibited bacterial attachment as biofilm formation. Alpha mangostin down-regulated genes associated with the formation of persister cells and biofilms, such as norA, norB, dnaK, groE, and mepR, ranging from 2 to 4-folds. Alpha mangostin at 16 μg/ml was non-toxic (> 95% cell survival) to liver-derived HepG2 and lung-derived A549 cells, similarly. Still, alpha mangostin exhibited 50% cell lysis of human RBC at 16 μg/ml. Interestingly, alpha mangostin was effective in vivo at increasing the survival up to 75% (p<0.0001) of Galleria mellonella larvae infected with MRSA persister for 120 h. In conclusion, we report that alpha mangostin is active against MRSA persisters and biofilms, and these data further our understanding of the antistaphylococcal activity and toxicity of this natural compound.

Chemistry and bioactivities of natural steroidal alkaloids

Steroidal alkaloids possess the basic steroidal skeleton with a nitrogen atom in rings or side chains incorporated as an integral part of the molecule. They have demonstrated a wide range of biological activities, and some of them have even been developed as therapeutic drugs, such as abiraterone acetate (Zytiga®), a blockbuster drug, which has been used for the treatment of prostate cancer. Structurally diverse natural steroidal alkaloids present a wide spectrum of biological activities, which are attractive for natural product chemistry and medicinal chemistry communities. This review comprehensively covers the structural classification, isolation and various biological activities of 697 natural steroidal alkaloids discovered from 1926 to October 2021, with 363 references being cited.

n-Butanol Potentiates Subinhibitory Aminoglycosides against Bacterial Persisters and Multidrug-Resistant MRSA by Rapidly Enhancing Antibiotic Uptake

Potentiation of traditional antibiotics is of significance for combating antibiotic-resistant bacteria that have become a severe threat to human and animal health. Here, we report that 1 min co-treatment with n-butanol greatly and specifically enhances the bactericidal action of aminoglycosides by 5 orders of magnitude against stationary-phase Staphylococcus aureus cells, with n-propanol and isobutanol showing less potency. This combined treatment also rapidly kills various S. aureus persisters, methicillin-resistant S. aureus (MRSA) cells, and numerous Gram-positive and -negative pathogens including some clinically isolated multidrug-resistant pathogens (e.g., S. aureus, Staphylococcus epidermidis, and Enterococcus faecalis) in vitro, as well as S. aureus in mice. Mechanistically, the potentiation results from the actions of aminoglycosides on their conventional target ribosome rather than the antiseptic effect of n-butanol and is achieved by rapidly enhancing the bacterial uptake of aminoglycosides, while salts and inhibitors of proton motive force (e.g., CCCP) can diminish this uptake. Importantly, such n-butanol-enhanced antibiotic uptake even enables subinhibitory concentrations of aminoglycosides to rapidly kill both MRSA and conventional S. aureus cells. Given n-butanol is a non-metabolite in the pathogens we tested, our work may open avenues to develop a metabolite-independent strategy for aminoglycoside potentiation to rapidly eliminate antibiotic-resistant/tolerant pathogens, as well as for reducing the toxicity associated with aminoglycoside use.

The steroidal alkaloids α-tomatine and tomatidine: Panorama of their mode of action and pharmacological properties

The steroidal glycoalkaloid α-tomatine (αTM) and its aglycone tomatidine (TD) are abundant in the skin of unripe green tomato and present in tomato leaves and flowers. They mainly serve as defensive agents to protect the plant against infections by insects, bacteria, parasites, viruses, and fungi. In addition, the two products display a range of pharmacological properties potentially useful to treat various human diseases. We have analyzed all known pharmacological activities of αTM and TD, and the corresponding molecular targets and pathways impacted by these two steroidal alkaloids. In experimental models, αTM displays anticancer effects, particularly strong against androgen-independent prostate cancer, as well as robust antifungal effects. αTM is a potent cholesterol binder, useful as a vaccine adjuvant to improve delivery of protein antigens or therapeutic oligonucleotides. TD is a much less cytotoxic compound, able to restrict the spread of certain viruses (such as dengue, chikungunya and porcine epidemic diarrhea viruses) and to provide cardio and neuro-protective effects toward human cells. Both αTM and TD exhibit marked anti-inflammatory activities. They proceed through multiple signaling pathways and protein targets, including the sterol C24 methyltransferase Erg6 and vitamin D receptor, both directly targeted by TD. αTM is a powerful regulator of the NFkB/ERK signaling pathway implicated in various diseases. Collectively, the analysis shed light on the multitargeted action of αTM/TD and their usefulness as chemo-preventive or chemotherapeutic agents. A novel medicinal application for αTM is proposed.

Concise Large-Scale Synthesis of Tomatidine, A Potent Antibiotic Natural Product

Tomatidine has recently generated a lot of interest amongst the pharmacology, medicine, and biology fields of study, especially for its newfound activity as an antibiotic agent capable of targeting multiple strains of bacteria. In the light of its low natural abundance and high cost, an efficient and scalable multi-gram synthesis of tomatidine has been developed. This synthesis uses a Suzuki-Miyaura-type coupling reaction as a key step to graft an enantiopure F-ring side chain to the steroidal scaffold of the natural product, which was accessible from low-cost and commercially available diosgenin. A Lewis acid-mediated spiroketal opening followed by an azide substitution and reduction sequence is employed to generate the spiroaminoketal motif of the natural product. Overall, this synthesis produced 5.2 g in a single pass in 15 total steps and 15.2% yield using a methodology that is atom economical, scalable, and requires no flash chromatography purifications.

Exploring Phytochemicals for Combating Antibiotic Resistance in Microbial Pathogens

Antibiotic resistance or microbial drug resistance is emerging as a serious threat to human healthcare globally, and the multidrug-resistant (MDR) strains are imposing major hurdles to the progression of drug discovery programs. Newer antibiotic-resistance mechanisms in microbes contribute to the inefficacy of the existing drugs along with the prolonged illness and escalating expenditures. The injudicious usage of the conventional and commonly available antibiotics in human health, hygiene, veterinary and agricultural practices is proving to be a major driver for evolution, persistence and spread of antibiotic-resistance at a frightening rate. The drying pipeline of new and potent antibiotics is adding to the severity. Therefore, novel and effective new drugs and innovative therapies to treat MDR infections are urgently needed. Apart from the different natural and synthetic drugs being tested, plant secondary metabolites or phytochemicals are proving efficient in combating the drug-resistant strains. Various phytochemicals from classes including alkaloids, phenols, coumarins, terpenes have been successfully demonstrated their inhibitory potential against the drug-resistant pathogens. Several phytochemicals have proved effective against the molecular determinants responsible for attaining the drug resistance in pathogens like membrane proteins, biofilms, efflux pumps and bacterial cell communications. However, translational success rate needs to be improved, but the trends are encouraging. This review highlights current knowledge and developments associated challenges and future prospects for the successful application of phytochemicals in combating antibiotic resistance and the resistant microbial pathogens.

Counteracting Bacterial Motility: A Promising Strategy to Narrow Listeria monocytogenes Biofilm in Food Processing Industry

Listeria monocytogenes (L. monocytogenes) is often associated with processed food as it can form biofilms that represent a source of contamination at all stages of the manufacturing chain. The control and prevention of biofilms in food-processing plants are of utmost importance. This study explores the efficacy of prospect molecules for counteracting bacterial mechanisms leading to biofilm formation. The compounds included the phytomolecule tomatidine, zinc chloride (ZnCl₂), ethylenediaminetetraacetic acid (EDTA), and a more complexed mixture of bacterial compounds from coagulase-negative staphylococci (CNS exoproducts). Significant inhibition of L. monocytogenes biofilm formation was evidenced using a microfluidic system and confocal microscopic analyses (p < 0.001). Active molecules were effective at an early stage of biofilm development (≥50% of inhibition) but failed to disperse mature biofilms of L. monocytogenes. According to our findings, prevention of surface attachment was associated with a disruption of bacterial motility. Indeed, agar cell motility assays demonstrated the effectiveness of these molecules. Overall, results highlighted the critical role of motility in biofilm formation and allow to consider flagellum-mediated motility as a promising molecular target in control strategies against L. monocytogenes in food processing environments.

Photolysis of methicillin-resistant Staphylococcus aureus using Cu-doped carbon spheres

Developing alternative treatment strategies against methicillin-resistant Staphylococcus aureus (MRSA) infections is a challenge but could have many potential applications. In this paper, we developed a novel approach to eradicate MRSA through photolysis of the staphyloxanthin (STX) pigment found within the MRSA membranes and intracellular molecules (e.g. genomic DNA and proteins). Specifically, Cu-doped hollow carbon spheres (Cu-HCSs) were employed here for antibacterial treatment. Unlike blue-light treatment alone, which only "injured" MRSA, Cu-HCSs in combination with blue-light irradiation promoted photobleaching of STX to destroy membrane integrity, and further caused oxidative cleavage of DNA and proteins inside MRSA, working as a nuclease/protease mimicking nanozyme, resulting in efficient killing of MRSA. Mechanism analysis showed that the cleavage activity resulted from the elevated levels of singlet oxygen (1O2) generated from the photosensitized oxidation of Cu-HCSs. Further animal studies demonstrated that the photolysis activity of Cu-HCSs could be used to treat subcutaneous abscesses and bacteremia caused by MRSA. Thus, this photolysis-based antibacterial platform may help avoid bacterial resistance, with the potential to kill multidrug resistant bacteria.

Targeting the ATP Synthase in Staphylococcus aureus Small Colony Variants, Streptococcus pyogenes and Pathogenic Fungi

The ATP synthase has been validated as a druggable target with the approval of the ATP synthase inhibitor, bedaquiline, for treatment of drug-resistant Mycobacterium tuberculosis, a bacterial species in which the ATP synthase is essential for viability. Gene inactivation studies have also shown that the ATP synthase is essential among Streptococci, and some studies even suggest that inhibition of the ATP synthase is a strategy for the elimination of Staphylococcus aureus small colony variants with deficiencies in the electron transport chain, as well as pathogenic fungi, such as Candida albicans. Here we investigated five structurally diverse ATP synthase inhibitors, namely N,N′-dicyclohexylcarbodiimide (DCCD), oligomycin A, tomatidine, resveratrol and piceatannol, for their growth inhibitory activity against the bacterial strains Streptococcus pyogenes, S. aureus and two isogenic small colony variants, as well as the pathogenic fungal species, C. albicans and Aspergillus niger. DCCD showed broad-spectrum inhibitory activity against all the strains (minimum inhibitory concentration (MIC) 2–16 µg/mL), except for S. aureus, where the ATP synthase is dispensable for growth. Contrarily, oligomycin A selectively inhibited the fungal strains (MIC 1–8 µg/mL), while tomatidine showed very potent, but selective, activity against small colony variants of S. aureus with compromised electron transport chain activity (MIC 0.0625 µg/mL). Small colony variants of S. aureus were also more sensitive to resveratrol and piceatannol than the wild-type strain, and piceatannol inhibited S. pyogenes at 16–32 µg/mL. We previously showed that transposon inactivation of the ATP synthase sensitizes S. aureus towards polymyxin B and colistin, and here we demonstrate that treatment with structurally diverse ATP synthase inhibitors sensitized S. aureus towards polymyxin B. Collectively, our data show that ATP synthase inhibitors can have selective inhibitory activity against pathogenic microorganisms in which the ATP synthase is essential. The data also show that the inhibition of the ATP synthase in Streptococcus pyogenes may be a new strategy for development of a narrow-spectrum antibiotic class. In other major bacterial pathogens, such as S. aureus and potentially Escherichia coli, where the ATP synthase is dispensable, the ATP synthase inhibitors may be applied in combination with antimicrobial peptides to provide new therapeutic options.

Combination With Tomatidine Improves the Potency of Posaconazole Against Trypanosoma cruzi

Azoles such as posaconazole (Posa) are highly potent against Trypanosoma cruzi. However, when tested in chronic Chagas disease patients, a high rate of relapse after Posa treatment was observed. It appears that inhibition of T. cruzi cytochrome CYP51, the target of azoles, does not deliver sterile cure in monotherapy. Looking for suitable combination partners of azoles, we have selected a set of inhibitors of sterol and sphingolipid biosynthetic enzymes. A small-scale phenotypic screening was conducted in vitro against the proliferative forms of T. cruzi, extracellular epimastigotes and intracellular amastigotes. Against the intracellular, clinically relevant forms, four out of 15 tested compounds presented higher or equal activity as benznidazole (Bz), with EC₅₀ values ≤2.2 μM. Ro48-8071, an inhibitor of lanosterol synthase (ERG7), and the steroidal alkaloid tomatidine (TH), an inhibitor of C-24 sterol methyltransferase (ERG6), exhibited the highest potency and selectivity indices (SI = 12 and 115, respectively). Both were directed to combinatory assays using fixed-ratio protocols with Posa, Bz, and fexinidazole. The combination of TH with Posa displayed a synergistic profile against amastigotes, with a mean ΣFICI value of 0.2. In vivo assays using an acute mouse model of T. cruzi infection demonstrated lack of antiparasitic activity of TH alone in doses ranging from 0.5 to 5 mg/kg. As observed in vitro, the best combo proportion in vivo was the ratio 3 TH:1 Posa. The combination of Posa at 1.25 mpk plus TH at 3.75 mpk displayed suppression of peak parasitemia of 80% and a survival rate of 60% in the acute infection model, as compared to 20% survival for Posa at 1.25 mpk alone and 40% for Posa at 10 mpk alone. These initial results indicate a potential for the combination of posaconazole with tomatidine against T. cruzi.

Novel Treatments and Preventative Strategies Against Food-Poisoning Caused by Staphylococcal Species

Staphylococcal infections are a widespread cause of disease in humans. In particular, S. aureus is a major causative agent of infection in clinical medicine. In addition, these bacteria can produce a high number of staphylococcal enterotoxins (SE) that may cause food intoxications. Apart from S. aureus, many coagulase-negative Staphylococcus spp. could be the source of food contamination. Thus, there is an active research work focused on developing novel preventative interventions based on food supplements to reduce the impact of staphylococcal food poisoning. Interestingly, many plant-derived compounds, such as polyphenols, flavonoids, or terpenoids, show significant antimicrobial activity against staphylococci, and therefore these compounds could be crucial to reduce the incidence of food intoxication in humans. Here, we reviewed the most promising strategies developed to prevent staphylococcal food poisoning.

Antifungal activity and antidiarrheal activity via antimotility mechanisms of (-)-fenchone in experimental models

BACKGROUND

(-)-Fenchone is a bicyclic monoterpene present in essential oils of plant species, such as Foeniculum vulgare and Peumus boldus, used to treatment of gastrointestinal diseases. Pharmacological studies report its anti-inflammatory, antioxidant, and antinociceptive activity.

AIM

To investigate antidiarrheal activity related to gastrointestinal motility, intestinal secretion and antimicrobial activity.

METHODS

A castor oil-induced diarrhea model was used to evaluate antidiarrheal activity. Intestinal transit and gastric emptying protocols were used to assess a possible antimotility effect. Muscarinic receptors, presynaptic α₂-adrenergic and tissue adrenergic receptors, K_ATP channels, nitric oxide were investigated to uncover antimotility mechanisms of action and castor oil-induced enteropooling to elucidate antisecretory mechanisms. The antimicrobial activity was evaluated in the minimum inhibitory concentration model, the fractional inhibitory concentration index using the (-)-fenchone association method with standard antifungal agents.

RESULTS

(-)-Fenchone (75, 150 and 300 mg/kg) showed antidiarrheal activity, with a significant decrease in the evacuation index. This activity is possibly related to a percentage of reduced intestinal transit (75, 150 and 300 mg/kg). The antimotility effect of (-)-fenchone decreased in the presence of pilocarpine, yohimbine, propranolol, L-NG-nitroarginine methyl ester or glibenclamide. In the enteropooling model, no reduction in intestinal fluid weight was observed. (-)- Fenchone did not show antibacterial activity; on the other hand, inhibits the growth of strains of fungi with a minimum fungicide concentration of 32 μg/mL. However, when it was associated with amphotericin B, no synergism was observed.

CONCLUSION

The antidiarrheal effect of (-)-fenchone in this study involves antimotility effect and not involve antisecretory mechanisms. (-)-Fenchone presents antifungal activity; however, it did not show antibacterial activity.

Persistence of Staphylococcus aureus: Multiple Metabolic Pathways Impact the Expression of Virulence Factors in Small-Colony Variants (SCVs)

Staphylococcus aureus is able to survive within host cells by switching its phenotype to the small-colony variant (SCV) phenotype. The emergence of SCVs is associated with the development of persistent infections, which may be both chronic and recurrent. This slow-growing subpopulation of S. aureus forms small colonies on solid-medium agar, is induced within host cells, presents a non-homogenous genetic background, has reduced expression of virulence factors and presents a variable phenotype (stable or unstable). While virtually all SCVs isolated from clinical specimens can revert to the parental state with rapid growth, the stable SCVs recovered in clinical specimens have been found to contain specific mutations in metabolic pathways. In contrast, other non-stable SCVs are originated from regulatory mechanisms involving global regulators (e.g., sigB, sarA, and agr) or other non-defined mutations. One major characteristic of SCVs was the observation that SCVs were recovered from five patients with infections that could persist for decades. In these five cases, the SCVs had defects in electron transport. This linked persistent infections with SCVs. The term "persistent infection" is a clinical term wherein bacteria remain in the host for prolonged periods of time, sometimes with recurrent infection, despite apparently active antibiotics. These terms were described in vitro where bacteria remain viable in liquid culture medium in the presence of antibiotics. These bacteria are called "persisters". While SCVs can be persisters in liquid culture, not all persisters are SCVs. One mechanism associated with the metabolically variant SCVs is the reduced production of virulence factors. SCVs have consistently shown reduced levels of RNAIII, a product of the accessory gene regulatory (agrBDCA) locus that controls a quorum-sensing system and regulates the expression of a large number of virulence genes. Reduced Agr acitivity is associated with enhanced survival of SCVs within host cells. In this review, we examine the impact of the SCVs with altered metabolic pathways on agr, and we draw distinctions with other types of SCVs that emerge within mammalian cells with prolonged infection.

Venturicidin A, A Membrane-active Natural Product Inhibitor of ATP synthase Potentiates Aminoglycoside Antibiotics

Despite the remarkable advances due to the discovery and development of antimicrobials agents, infectious diseases remain the second leading cause of death worldwide. This fact underlines the importance of developing new therapeutic strategies to address the widespread antibiotic resistance, which is the major contributing factor for clinical failures of the current therapeutics. In a screen for antibiotic adjuvants, we identified a natural product from actinomycetes, venturicidin A (VentA), that potentiates the aminoglycoside antibiotic gentamicin against multidrug-resistant clinical isolates of Staphylococcus, Enterococcus, and Pseudomonas aeruginosa. Furthermore, the combination of gentamicin and VentA was bactericidal and rapidly eradicated methicillin-resistant S. aureus (MRSA). The molecular mechanism of gentamicin potentiation activity is attributed to uncoupling of ATP synthesis by VentA from electron transport presumably by blocking the proton flow through ATP synthase, which results in an elevated concentration of extracellular protons and subsequent anticipated raise in gentamicin uptake. The disruption of the proton flux was characterized by perturbed membrane potential in MRSA. These results demonstrate that inhibition of ATP synthase along with the subsequent membrane dysregulation, as shown here with VentA, complements aminoglycoside antibiotics against MDR bacteria, and that this approach may be employed to combat bacterial resistance.

Bactericidal Activity of the Bacterial ATP Synthase Inhibitor Tomatidine and the Combination of Tomatidine and Aminoglycoside Against Persistent and Virulent Forms of Staphylococcus aureus

Tomatidine (TO), a steroid alkaloid, exerts a strong bactericidal activity on the infection-persistent phenotype of Staphylococcus aureus, the small-colony variant (SCV), with a minimal inhibitory concentration (MIC) of 0.06 μg/ml. Also, the combination of TO to an aminoglycoside (AMG) shows a strong synergistic effect against prototypical (WT) S. aureus (MIC 0.06 μg/ml), which is otherwise unaffected by TO alone (MIC > 128 μg/ml). We have recently established that the ATP synthase (subunit AtpE) was the molecular target of TO and that TO reduces the production of ATP in S. aureus. The purpose of this study was to understand how TO and the TO-AMG combination exert bactericidal activities against S. aureus SCV and WT strains, respectively. The impact of TO and of the TO-gentamicin (GEN) combination on the membrane potential and generation of reactive oxygen species (ROS) were determined using florescent probes. GEN uptake in WT was assessed in the presence of TO. Virulence of SCV and WT strains as well as of in vitro-selected mutants showing resistance to TO or the TO-GEN combination was evaluated in a murine thigh infection model. TO causes a reduction in membrane potential in both WT and SCV, but significant amounts of ROS are only produced in SCVs. Besides, the presence of TO improves the uptake of GEN by the WT strain and the combination TO-GEN generated 2.5-folds more ROS in WT, compared to that induced by GEN alone. Under anaerobic conditions, WT adopts a fermentative slow-growth phenotype and becomes susceptible to TO even if used alone. In vivo, TO- or TO-GEN-resistant strains were significantly altered in their ability to colonize tissues. These results shed light on the mechanism of action of TO and its synergy with AMGs against S. aureus WT. TO bactericidal activity against SCVs is attributable to both a critical drop in the membrane potential accompanied by a substantial ROS production. In the WT, TO helps GEN uptake and ROS is also important for the synergy. Acquiring resistance to TO significantly impairs virulence. The residual ATP synthase activity of SCVs might represent the Achilles’ heel of persistent S. aureus.

Virulence Characteristics of mecA-Positive Multidrug-Resistant Clinical Coagulase-Negative Staphylococci

Coagulase-negative staphylococci (CoNS) are an important group of opportunistic pathogenic microorganisms that cause infections in hospital settings and are generally resistant to many antimicrobial agents. We report on phenotypic and genotypic virulence characteristics of a select group of clinical, mecA-positive (encoding penicillin-binding protein 2a) CoNS isolates. All CoNS were resistant to two or more antimicrobials with S. epidermidis strain 214EP, showing resistance to fifteen of the sixteen antimicrobial agents tested. Aminoglycoside-resistance genes were the ones most commonly detected. The presence of megaplasmids containing both horizontal gene transfer and antimicrobial resistance genetic determinants indicates that CoNS may disseminate antibiotic resistance to other bacteria. Staphylococcus sciuri species produced six virulence enzymes, including a DNase, gelatinase, lipase, phosphatase, and protease that are suspected to degrade tissues into nutrients for bacterial growth and contribute to the pathogenicity of CoNS. The PCR assay for the detection of biofilm-associated genes found the eno (encoding laminin-binding protein) gene in all isolates. Measurement of their biofilm-forming ability and Spearman’s rank correlation coefficient analyses revealed that the results of crystal violet (CV) and extracellular polymeric substances (EPS) assays were significantly correlated (ρ = 0.9153, P = 3.612e-12). The presence of virulence factors, biofilm-formation capability, extracellular enzymes, multidrug resistance, and gene transfer markers in mecA-positive CoNS clinical strains used in this study makes them powerful opportunistic pathogens. The study also warrants a careful evaluation of nosocomial infections caused by CoNS and may be useful in studying the mechanism of virulence and factors associated with their pathogenicity in vivo and developing effective strategies for mitigation.

Tomatidine Alleviates Osteoporosis by Downregulation of p53

Background

As a common metabolic disorder, osteoporosis is characterized by decreasing bone mass density and increased possibility of fragility fracture. The incidence of senile osteoporosis increases year by year. There is no gold standard of treatment for osteoporosis. Tomatidine is the aglycone derivative of tomatine, having the ability to treat various diseases, including osteoporosis. However, the mechanism by which tomatidine improves osteoporosis has not been fully elucidated. Tomatidine is a potential and promising drug for osteoporosis.

Material/Methods

In this study, the KEGG pathways that tomatidine-targeted genes enriched in were obtained using bioinformatics methods. The KEGG pathways involved in osteoporosis that were also associated with tomatidine-targeted genes were selected. After analysis of these pathways, essential genes that may be involved in this biological process were identified and validated experimentally.

Results

We found 110 osteoporosis related KEGG pathways and 76 tomatidine-targeted genes-related KEGG pathways were obtained. 39 shared KEGG pathways were identified. The top 5 pathways were: pathway of chronic myeloid leukemia, pathway of B cell receptor signaling, pathway in cancer, bladder cancer pathway, and progesterone-mediated oocyte maturation pathway. MAPK1, MAP2K1, MAPK3, RAF1 were involved in all the 5 pathways. The p53 signaling pathway and the MAPK signaling pathway were involved in the 5 KEGG pathways. In vitro experiments showed that downregulating p53 expression could be potentially protective for osteoporosis.

Conclusions

Tomatidine can improve osteoporosis, and one of the mechanisms of its action is achieved by modulating p53. Tomatidine may be a promising drug for osteoporosis.

5-Methylindole Potentiates Aminoglycoside Against Gram-Positive Bacteria Including Staphylococcus aureus Persisters Under Hypoionic Conditions

Antibiotic resistance/tolerance has become a severe threat to human and animal health. To combat antibiotic-resistant/tolerant bacteria, it is of significance to improve the efficacy of traditional antibiotics. Here we show that indole potentiates tobramycin to kill stationary-phase Staphylococcus aureus cells after a short, combined treatment, with its derivative 5-methylindole being the most potent compound tested and with the absence of ions as a prerequisite. Consistently, this combined treatment also kills various types of S. aureus persister cells as induced by the protonophore CCCP, nutrient shift, or starvation, as well as methicillin-resistant S. aureus (MRSA) cells. Importantly, 5-methylindole potentiates tobramycin killing of S. aureus persisters in a mouse acute skin wound model. Furthermore, 5-methylindole facilitates killing of many strains of gram-positive pathogens such as Staphylococcus epidermidis, Enterococcus faecalis, and Streptococcus pyogenes by aminoglycoside antibiotics, whereas it suppresses the action of aminoglycoside against the gram-negative pathogens Escherichia coli and Shigella flexneri. In conclusion, our work may pave the way for the development of indole derivatives as adjuvants to potentiate aminoglycosides against gram-positive pathogens.

Despite Antagonism in vitro, Pseudomonas aeruginosa Enhances Staphylococcus aureus Colonization in a Murine Lung Infection Model

Staphylococcus aureus and Pseudomonas aeruginosa are prevalent lung pathogens in cystic fibrosis (CF). Whereas co-infection worsens the clinical outcome, prototypical strains are usually antagonistic in vitro. We sought to resolve the discrepancy between these in vitro and in vivo observations. In vitro, growth kinetics for co-cultures of co-isolates from CF patients showed that not all P. aeruginosa strains affected S. aureus viability. On solid media, S. aureus slow-growing colonies were visualized around some P. aeruginosa strains whether or not S. aureus viability was reduced in liquid co-cultures. The S. aureus-P. aeruginosa interactions were then characterized in a mouse lung infection model. Lung homogenates were plated on selective media allowing colony counts of either bacterium. Overall, 35 P. aeruginosa and 10 S. aureus strains (clinical, reference, and mutant strains), for a total of 200 co-infections, were evaluated. We observed that S. aureus colonization of lung tissues was promoted by P. aeruginosa and even by strains showing antagonism in vitro. Promotion was proportional to the extent of P. aeruginosa colonization, but no correlation was found with the degree of myeloperoxidase quantification (as marker of inflammation) or with specific virulence-associated factors using known mutant strains of S. aureus and P. aeruginosa. On the other hand, P. aeruginosa significantly increased the expression of two possible cell receptors for S. aureus, i.e., ICAM-1 and ITGA-5 (marker for integrin α₅β₁) in lung tissue, while mono-infections by S. aureus did not. This study provides insights on polymicrobial interactions that may influence the progression of CF-associated pulmonary infections.

Therapeutic value of steroidal alkaloids in cancer: Current trends and future perspectives

Discovery and development of new potentially selective anticancer agents are necessary to prevent a global cancer health crisis. Currently, alternative medicinal agents derived from plants have been extensively investigated to develop anticancer drugs with fewer adverse effects. Among them, steroidal alkaloids are conventional secondary metabolites that comprise an important class of natural products found in plants, marine organisms and invertebrates, and constitute a judicious choice as potential anti-cancer leads. Traditional medicine and modern science have shown that representatives from this compound group possess potential antimicrobial, analgesic, anticancer and anti-inflammatory effects. Therefore, systematic and recapitulated information about the bioactivity of these compounds, with special emphasis on the molecular or cellular mechanisms, is of high interest. In this review, we methodically discuss the in vitro and in vivo potential of the anticancer activity of natural steroidal alkaloids and their synthetic and semi-synthetic derivatives. This review focuses on cumulative and comprehensive molecular mechanisms, which will help researchers understand the molecular pathways involving steroid alkaloids to generate a selective and safe new lead compound with improved therapeutic applications for cancer prevention and therapy. In vitro and in vivo studies provide evidence about the promising therapeutic potential of steroidal alkaloids in various cancer cell lines, but advanced pharmacokinetic and clinical experiments are required to develop more selective and safe drugs for cancer treatment.

Protein expression profiles in methicillin-resistant Staphylococcus aureus (MRSA) under effects of subminimal inhibitory concentrations of imipenem

Imipenem is a beta-lactam antibiotic mainly active against gram-negative bacterial pathogens and also could cause cell wall impairment in methicillin-resistant Staphylococcus aureus(MRSA). However, related antibacterial mechanisms of imipenem on MRSA and mixed infections of MRSA and gram-negative bacteria are relatively poorly revealed. This study was to identify proteins in the MRSA response to subminimal inhibitory concentrations (sub-MICs) of imipenem treatment. Our results showed that 240 and 58 different expression proteins (DEPs) in sub-MICs imipenem-treated S3 (a standard MRSA strain) and S23 (a clinical MRSA strain) strains were identified through the isobaric tag for relative and absolute quantitation method when compared with untreated S3 and S23 strains, respectively, which was further confirmed by multiple reactions monitoring. Our result also demonstrated that expressions of multiple DEPs involved in cellular proliferation, metabolism and virulence were significantly changed in S3 and S23 strains, which was proved by gene ontology annotations and qPCR analysis. Further, transmission electron microscopy and scanning electron microscopy analysis showed cell wall deficiency, cell lysis and abnormal nuclear mitosis on S23 strain. Our study provides important information for understanding the antibacterial mechanisms of imipenem on MRSA and for better usage of imipenem on patients co-infected with MRSA and other multidrug-resistant gram-negative bacteria.

The Anti-virulence Efficacy of 4-(1,3-Dimethyl-2,3-Dihydro-1H-Benzimidazol-2-yl)Phenol Against Methicillin-Resistant Staphylococcus aureus

Antimicrobial drug discovery against drug-resistant bacteria is an urgent need. Beyond agents with direct antibacterial activity, anti-virulent molecules may also be viable compounds to defend against bacterial pathogenesis. Using a high throughput screen (HTS) that utilized Caenorhabditis elegans infected with methicillin-resistant Staphylococcus aureus (MRSA) strain of MW2, we identified 4-(1,3-dimethyl-2,3-dihydro-1H-benzimidazol-2-yl)phenol (BIP). Interestingly, BIP had no in vitro inhibition activity against MW2, at least up to 64 μg/ml. The lack of direct antimicrobial activity suggests that BIP could inhibit bacterial virulence factors. To explore the possible anti-virulence effect of the identified molecule, we first performed real-time PCR to examine changes in virulence expression. BIP was highly active against MRSA virulence factors at sub-lethal concentrations and down-regulated virulence regulator genes, such as agrA and codY. However, the benzimidazole derivatives omeprazole and pantoprazole did not down-regulate virulence genes significantly, compared to BIP. Moreover, the BIP-pretreated MW2 cells were more vulnerable to macrophage-mediated killing, as confirmed by intracellular killing and live/dead staining assays, and less efficient in establishing a lethal infection in the invertebrate host Galleria mellonella (p = 0.0131). We tested the cytotoxicity of BIP against human red blood cells (RBCs), and it did not cause hemolysis at the highest concentration tested (64 μg/ml). Taken together, our findings outline the potential anti-virulence activity of BIP that was identified through a C. elegans-based, whole animal based, screen.

Review on plant antimicrobials: a mechanistic viewpoint

Microbial resistance to classical antibiotics and its rapid progression have raised serious concern in the treatment of infectious diseases. Recently, many studies have been directed towards finding promising solutions to overcome these problems. Phytochemicals have exerted potential antibacterial activities against sensitive and resistant pathogens via different mechanisms of action. In this review, we have summarized the main antibiotic resistance mechanisms of bacteria and also discussed how phytochemicals belonging to different chemical classes could reverse the antibiotic resistance. Next to containing direct antimicrobial activities, some of them have exerted in vitro synergistic effects when being combined with conventional antibiotics. Considering these facts, it could be stated that phytochemicals represent a valuable source of bioactive compounds with potent antimicrobial activities.

Ouabain potentiates the antimicrobial activity of aminoglycosides against Staphylococcus aureus

Background

Staphylococcus aureus is a notorious pathogen which often causes nosocomial and community attained infections. These infections steadily increased after evolving the resistance due to indecorous practice of antibiotics and now become a serious health issue. Ouabain is a Na⁺/K⁺-ATPase inhibitor that leads to increase the heart contraction in patients with congestive heart failure.

Methods

In the present study, in vitro antimicrobial effect of ouabain together with aminoglycosides was determined against clinical and non-clinical S. aureus strains. Using checkerboard, Gentamycin uptake and biofilm assays, we analysed he interactions of ouabain with aminoglycosides.

Results

Ouabain induced the staphylocidal potency of aminoglycosides by remarkably reducing the MIC of gentamycin (GEN) by 16 (0.25 μg/mL), 8 folds (0.5 μg/mL) amikacin (AMK); and 16 folds (1.0 μg/mL) with kanamycin (KAN), compared to their individual doses. OBN severely reduced cell viability within 60 min with GEN (1 μg/mL), KAN (2 μg/mL) and 90 min with AMK (1 μg/mL). This bactericidal effect was enhanced due to GEN uptake potentiated by 66% which led to increase the cell permeability as revealed by leakage of bacterial ATP and nitrocefin assay. The biofilm adherence disrupted by 80 and 50% at 5 mg/mL and 1.5 mg/mL OBN and 50 and 90% biofilm formation was inhibited at 5 mg/mL (MBIC₅₀) and 10 mg/mL (MBIC₉₀), respectively. Moreover, OBN with GEN further induced biofilm inhibition by 67 ± 5% at pH 7.0.

Conclusions

Taken together, we established that OBN synergizes the antimicrobial activity of aminoglycosides that induces cell killing due to intracellular accumulation of GEN by disturbing cell homeostasis. It may be proven an effective approach for the treatment of staphylococcal infections.

Respiration and Small Colony Variants of Staphylococcus aureus

Respiratory mutants, both naturally occurring and genetically constructed, have taught us about the importance of metabolism in influencing virulence factor production, persistence, and antibiotic resistance. As we learn more about small colony variants, we find that Staphylococcus aureus has many pathways to produce small colony variants, although the respiratory variants are the best described clinically and in the laboratory.

Immunomodulatory molecules regulate adhesin gene expression in Staphylococcus aureus: Effect on bacterial internalization into bovine mammary epithelial cells

Staphylococcus aureus is a major pathogen of subclinical bovine mastitis that usually is chronic and recurrent, which has been related to its ability to internalize into bovine mammary epithelial cells (bMECs). Previously, we reported that short and medium fatty acids and cholecalciferol reduce S. aureus internalization into pretreated-bMECs with these molecules suggesting a role as immunomodulatory agents. Hence, we assessed the role of sodium butyrate (NaB), sodium octanoate (NaO) and cholecalciferol on S. aureus adhesin expression and its internalization into bMECs. S. aureus pre-treated 2 h with 0.5 mM or 2 mM NaB showed a reduction in internalization into bMECs (∼35% and ∼55%; respectively), which coincided with a down-regulated expression of clumping factor B (ClfB). Also, the S. aureus internalization reduction by 2 mM NaB (2 h) agreed with a down-regulated expression of sdrC. Moreover, the 2 mM NaB (24 h) pre-treatment induced bacterial internalization (∼3-fold), which was related with an up-regulation of spa, clfB and sdrC genes. Also, NaO (0.25 mM and 1 mM) only reduced S. aureus internalization when bacteria were grown 2 h with this molecule but there was no relationship with adhesin expression. In addition, cholecalciferol (50 nM) reduced bacteria internalization at similar levels (∼50%) when bacteria were grown 2 and 24 h in broth supplemented with this compound, which correlated with spa and sdrC mRNA expression down-regulated at 2 h, and fnba and clfB mRNA expression decreased at 24 h. In conclusion, our data support the fact that fatty acids and cholecalciferol regulate adhesin gene expression as well as bacteria internalization in nonprofessional phagocytic cells, which may lead to development of anti-virulence agents for control of pathogens.

Gentisaldehyde and Its Derivative 2,3-Dihydroxybenzaldehyde Show Antimicrobial Activities Against Bovine Mastitis Staphylococcus aureus

Bovine mastitis is a worldwide disease of dairy cattle associated with significant economic losses for the dairy industry. One of the most common pathogens responsible for mastitis is Staphylococcus (S.) aureus. Due to the development and spreading of antibiotic resistance, the search for novel antimicrobial substances against S. aureus is of great importance. The aim of this study was to evaluate two dihydroxybenzaldehydes for the prevention of bovine mastitis. Therefore we determined the minimal inhibitory concentration (MICs) of gentisaldehyde (2,5-dihydroxybenzaldehyde) and 2,3-dihydroxybenzaldehyde of a diverse set of 172 bovine mastitis S. aureus isolates using an automated robot-based microdilution method. To characterize the bovine isolates we determined the genotype by spa-typing, the antimicrobial resistance to eight antibiotic classes using the disk diffusion method and the MICs of three commonly used antiseptics (benzalkonium chloride, chlorhexidine, and iodine). Further we investigated the cytotoxicity of gentisaldehyde and 2,3-dihydroxybenzaldehyde in bovine mammary epithelial MAC-T cells using the XTT assay. The S. aureus strains showed a high genetic diversity with 52 different spa-types, including five novel types. Antibiotic susceptibility testing revealed that 24% of isolates were resistant to one antimicrobial agent and 3% of isolates were multi-resistant. The occurrence of antibiotic resistance strongly correlated with the spa-type. Both dihydroxybenzaldehydes showed antimicrobial activities with a MIC50 of 500 mg/L. The MIC of gentisaldehyde significantly correlated with that of 2,3-dihydroxybenzaldehyde, whereas no correlation was observed with the MIC of the three antiseptics. Cytotoxicity testing using bovine mammary epithelial MAC-T cells revealed that gentisaldehyde and 2,3-dihydroxybenzaldehyde show low toxicity at MIC50 and MIC90 concentrations. In conclusion, gentisaldehyde and 2,3-dihydroxybenzaldehyde exhibited antimicrobial activities against a diverse range of bovine mastitis S. aureus strains at low-cytotoxic concentrations. Therefore, both compounds are potential candidates as antiseptics to prevent bovine mastitis and to reduce the use of antibiotics in dairy cows.

Influence of subinhibitory concentrations of NH125 on biofilm formation & virulence factors of Staphylococcus aureus

AIM

l-benzyl-3-cetyl-2-methylimidazolium iodide (NH125) can inhibit Staphylococcus aureus growth. We investigated the effects of sub-MIC concentrations of NH125 on S. aureus biofilm and virulence. Methodology & results: Three strains of S. aureus were tested. Sub-lethal concentrations of NH125 repressed biofilm formation. At partial sub-MICs, NH125 downregulated the expression of most virulence, while strain-dependent effects were found in the production of α-hemolysin, δ-hemolysin, coagulase and nuclease. In Galleria mellonella model, methicillin-resistant S. aureus pre-exposed to NH125 demonstrated significantly lower killing (p = 0.032 for 1/16 and 1/8 MICs; 0.008 for 1/4 MIC; and 0.001 for 1/2 MIC).

CONCLUSION

Sub-MIC concentrations of NH125 inhibited biofilm formation and virulence of S. aureus. These findings provide further support for evaluating the clinical efficacy of NH125 in staphylococcal infection.

Developments in strategies for Quorum Sensing virulence factor inhibition to combat bacterial drug resistance

Quorum sensing (QS) is a complex bacterial intercellular communication system. It is mediated by molecules called auto-inducers (AIs) and allows coordinated responses to a variety of environmental signals by inducing alterations in gene expression. Communication through QS can tremendously stimulate the pathogenicity and virulence via multiple mechanisms in pathogenic bacteria. The present review explores the major types of multitudinous QS systems known in Gram-positive and Gram-negative bacteria and their roles in bacterial pathogenesis and drug resistance. Because bacterial resistance to antibiotics is increasingly becoming a significant clinical challenge to human health; alternate strategies to combat drug resistance are warranted. Targeting bacterial pathogenicity by interruptions in QS using natural QS inhibitors and synthetic quorum-quenching analogs are being increasingly considered for development of next generation antimicrobials. The review highlights the recent advancements in discovery of promising new QS modulators and their efficiency in controlling infections caused by multidrug-resistant bacterial pathogens.

α-Chaconine and α-Solanine Inhibit RL95-2 Endometrium Cancer Cell Proliferation by Reducing Expression of Akt (Ser473) and ERα (Ser167)

The aim of this study is to investigate the potential inhibitory effect of α-chaconine and α-solanine on RL95-2 estrogen receptor (ER) positive human endometrial cancer cell line and to identify the effect of these glycoalkaloids on the Akt signaling and ERα. The cell proliferation profiles and the cytotoxicity studies were performed by Real-Time Cell Analyzer (xCELLigence) and compared with Sulphorhodamine B (SRB) assay. The effects of α-chaconine (2.5, 5, 10 µM), α-solanine (20, 30, 50 µM), API-1 (25 µM) and MPP (20 µM) effects on Akt (Ser473) and ERα (Ser167) expressions evaluated by Western blot and qPCR method. Their IC₅₀ values were as α-chaconine (4.72 µM) < MPP (20.01 µM) < α-solanine (26.27 µM) < API-1 (56.67 µM). 10 μM α-chaconine and 20, 30 and 50 μM α-solanine were effective in decreasing p-Akt(Ser473)/Akt ratio compared to positive control API-1. When the p-ERα/ERα ratios were evaluated, it was observed that α-chaconine (2.5, 5, 10 μM) and α-solanine (50 μM) were as effective as the specific ERα inhibitor MPP in reducing the ratio of p-ERα/ERα compared to the control group. In conclusion, it has been shown that the proliferation of α-chaconine and α-solanine in human endometrial carcinoma cells reduces the expression and activity of the Akt and ERα signaling pathway.