Proteome analyses of cellular proteins in methicillin-resistant Staphylococcus aureus treated with rhodomyrtone, a novel antibiotic candidate

A Novel Antibiotic, Rhodomyrtone: Pharmacokinetic Studies in a Murine Model and Optimization and Validation of High-Performance Liquid Chromatographic Method for Plasma Analysis

Rhodomyrtone has indisputable and undeniable potential as a new antibiotic for antibiotic-resistant Gram-positive bacteria. Therefore, the main objective of this study was to determine the pharmacokinetics profiles of orally administered rhodomyrtone in rats. A reverse-phase HPLC-UV method was developed, optimized and validated for the analysis of rhodomyrtone concentrations in rat plasma. The retention time of papaverine and rhodomyrtone was 3.928 and 5.937 min, with no interference with the excipients used. The lower limit of quantification (LLOQ) of rhodomyrtone in the plasma sample was 0.04 μg/mL, the accuracy of rhodomyrtone at the LLOQ level ranged from 93.64 to 106.36%, precision was 6.59%, 80-120% for accuracy and <20% CV for precision. The calibration curve was linear at concentrations ranging from 0.04 to 128 µg/mL with a correlation coefficient (r) value of equal to or greater than 0.999. Sprague Dawley rats received a single dose of rhodomyrtone at 50 and 100 mg/kg. Blood samples were collected from tail veins. The peak plasma concentration was observed at 2 h, and the area under the curve of rhodomyrtone at 50 mg/kg and 100 mg/kg was 3.41 ± 1.04 and 7.82 ± 1.53 μg·h/mL, respectively. The results demonstrated linear pharmacokinetics characteristics at the studied dosage range. The plasma concentration of rhodomyrtone was above the minimal inhibition concentrations of several common pathogenic bacteria of medical importance. The proposed HPLC-UV method is fast, cost-effective, reliable and reproducible, and it is proposed for the routine analysis of rhodomyrtone.

Transferosomes stabilized hydrogel incorporated rhodomyrtone-rich extract from Rhodomyrtus tomentosa leaf fortified with phosphatidylcholine for the management of skin and soft-tissue infections

Rhodomyrtus tomentosa leaf (RT)-incorporated transferosomes were developed with lecithin and cholesterol blends with edge activators at different ratios. RT-transferosomes were characterized and employed in transferosomal gel formulations for the management of skin and soft-tissue infections. The optimized formulation entrapped up to 81.90 ± 0.31% of RT with spherical vesicles (405.3 ± 2.0 nm), polydispersity index value of 0.16 ± 0.08, and zeta potential of - 61.62 ± 0.86 mV. Total phenolic and flavonoid contents of RT-transferosomes were 15.65 ± 0.04 μg GAE/g extract and 43.13 ± 0.91 μg QE/g extract, respectively. RT-transferosomes demonstrated minimum inhibitory and minimum bactericidal concentrations at 8-256 and 64-1024 μg/mL, respectively. Free radical scavenging assay showed RT-transferosomes with high scavenging activity against DPPH and ABTS radicals. Moreover, RT-transferosomes demonstrated moderate activity against mushroom tyrosinase, with IC50 values of 245.32 ± 1.32 μg/mL. The biocompatibility results against L929 fibroblast and Vero cells demonstrated IC50 at 7.05 ± 0.17 and 4.73 ± 0.13 μg/mL, respectively. In addition, nitric oxide production significantly decreased by 6.78-88.25% following the treatment with 31.2-500 ng/mL RT-transferosomes (p < 0.001). Furthermore, the freeze-thaw stability study displayed no significant change in stability in the sedimentation and pH of gel fortified with RT-transferosomes. The results suggested that RT-transferosome formulation can be effectively employed as natural biomedicines for scar prevention and the management of skin soft-tissue infections.

Health from Brazilian Amazon food wastes: Bioactive compounds, antioxidants, antimicrobials, and potentials against cancer and oral diseases

Brazilian Amazon contains over 30,000 plant species and foods rich in bioactive compounds such as terpenes, phenolic acids, alkaloids, and flavonoids, of potential health benefits (antioxidant, antimicrobial, antiparasitic, anticancer, gastroprotection, prebiotic effects, among others). The existence of residues from non-edible parts of plants (leaves, roots, stems, branches, barks) or fruit wastes (peel, bagasse, seeds) in the agri-food industry and its supply chain is an important challenge in food loss and waste management. In this critical review several Amazon species, focusing on extracts/essential oils from nonedible parts or wastes, were analyzed in terms of phytochemicals, biological activity, and underlying mechanisms. We hope this review emphasizes the importance of Amazon's sustainability initiatives on population health due to the potential shown against cancer, infectious diseases, and prevention of oral diseases. It is urgent to think about the conversion of amazon food wastes and co-products into high-added-value raw materials to develop novel drugs, food packaging systems, or nutraceutical foods.

Untargeted proteomic differences between clinical strains of methicillin-sensitive and methicillin-resistant Staphylococcusaureus

Staphylococcus aureus is a common disease-causing bacterium that has developed resistances to a wide variety of antibiotics. This increasing antibiotic resistance has made management of these infections difficult. A better understanding of the general differences among clinical S. aureus strains beyond the well characterized resistance mechanisms may help in identifying new anti-microbial targets. This study aimed to identify and compare the general differences in protein profiles among clinical strains of S. aureus sensitive and resistant to methicillin. The proteomic profiles of five methicillin sensitive (MSSA) and five methicillin resistant (MRSA) S. aureus strains were analyzed by ultra-performance liquid chromatography-mass spectrometry. Protein identification was done using Progenesis QI for Proteomics and the UniProt S. aureus database. Proteins that play roles in virulence, metabolism, and protein synthesis were found to be present at different abundances between MSSA and MRSA (Data available via ProteomeXchange with identifier PXD021629). This study shows differences in protein profiles between antibiotic sensitive and antibiotic resistant clinical strains of S. aureus that may affect the resistance mechanism. Further research on these differences may identify new drug targets against methicillin resistant S. aureus strains.

Unraveling the mechanisms of inhibition of silver-doped bioactive glass-ceramic particles

Infections are a major concern in orthopedics. Antibacterial agents such as silver ions are of great interest as broad-spectrum biocides and have been incorporated into bioactive glass-ceramic particles to control the release of ions within a therapeutic concentration and provide tissue regenerative properties. In this work, the antibacterial capabilities of silver-doped bioactive glass (Ag-BG) microparticles were explored to reveal the unedited mechanisms of inhibition against methicillin-resistant Staphylococcus aureus (MRSA). The antibacterial properties were not limited to the delivery of silver ions but rather a combination of antibacterial degradation by-products. For example, nano-sized debris punctured holes in bacteria membranes, osmotic effects, and reactive oxygen species causing oxidative stress and almost 40% of the inhibition. Upon successive Ag-BG treatments, MRSA underwent phenotypic and genomic mutations which were not only insufficient to develop resistance but instead, the clones became more sensitive as the treatment was re-delivered. Additionally, the unprecedented restorative functionality of Ag-BG allowed the effective use of antibiotics that MRSA resists. The synergy mechanism was mainly identified for combinations targeting cell-wall activity and their action was proven in biofilm-like and virulent conditions. Unraveling these mechanisms may offer new insights into how to tailor healthcare materials to prevent or debilitate infections and join the fight against antibiotic resistance in clinical cases.

Suppression of Thiol-Dependent Antioxidant System and Stress Response in Methicillin-Resistant Staphylococcus aureus by Docosanol: Explication Through Proteome Investigation

The present study was aimed to investigate the effect of docosanol on the protein expression profile of methicillin-resistant Staphylococcus aureus (MRSA). Thus, two-dimensional gel electrophoresis coupled with MALDI-TOF MS technique was utilized to identify the differentially regulated proteins in the presence of docosanol. A total of 947 protein spots were identified from the intracellular proteome of both control and docosanol treated samples among which 40 spots were differentially regulated with a fold change greater than 1.0. Prominently, the thiol-dependent antioxidant system and stress response proteins are downregulated in MRSA, which are critical for survival during oxidative stress. In particular, docosanol downregulated the expression of Tpx, AhpC, BshC, BrxA, and YceI with a fold change of 1.4 (p = 0.02), 1.4 (p = 0.01), 1.6 (p = 0.002), 4.9 (p = 0.02), and 1.4 (p = 0.02), respectively. In addition, docosanol reduced the expression of proteins involved in purine metabolic pathways, biofilm growth cycle, and virulence factor production. Altogether, these findings suggest that docosanol could efficiently target the antioxidant pathway by reducing the expression of bacillithiol and stress-associated proteins.

Proteomic and Transcriptomic Analyses Indicate Reduced Biofilm-Forming Abilities in Cefiderocol-Resistant Klebsiella pneumoniae

The advent of cefiderocol provides hope for the clinical treatment of multi-drug resistant gram-negative bacteria (GNB), especially those with carbapenem resistance. Resistance of Klebsiella pneumoniae to cefiderocol can be enhanced by acclimatization. In the present study, we collected cefiderocol resistant K. pneumoniae isolates during a 36-day acclimatization procedure while increasing the cefiderocol concentration in the culture medium. Strains were studied for changes in their biological characteristics using proteomics and transcriptomics. A decrease in biofilm formation ability was the main change observed among the induced isolates. Downregulation of genes involved in biofilm formation including hdeB, stpA, yhjQ, fba, bcsZ, uvrY, bcsE, bcsC, and ibpB were the main factors that reduced the biofilm formation ability. Moreover, downregulation of siderophore transporter proteins including the iron uptake system component efeO, the tonB-dependent receptor fecA, and ferric iron ABC transporter fbpA may be among the determining factors leading to cefiderocol resistance and promoting the reduction of biofilm formation ability of K. pneumoniae. This is the first study to investigate cefiderocol resistance based on comprehensive proteomic and transcriptomic analyses.

A Base-Mediated Approach Towards Dihydrofuro[2,3-b]Benzofurans from 2-Nitrobenzofurans and 1,3-Dicarbonyls

A straight-forward approach for the synthesis of a dihydrofuro[2,3-b]benzofuran derivatives has been achieved through a base-mediated Michael addition of 1,3-dicarbonyls to 2-nitrobenzofurans followed by intramolecular cyclization. A variety of 1,3-dicarbonyls, including cyclic as well as trifluoromethylated ones, have been subjected to react with 2-nitrobenzofurans under optimal conditions, and the respective dihydrofuro[2,3-b]benzofurans could be accessed in moderate to excellent yields.

Rhodomyrtone Accumulates in Bacterial Cell Wall and Cell Membrane and Inhibits the Synthesis of Multiple Cellular Macromolecules in Epidemic Methicillin-Resistant Staphylococcus aureus

As the burden of antibacterial resistance worsens and treatment options become narrower, rhodomyrtone—a novel natural antibiotic agent with a new antibacterial mechanism—could replace existing antibiotics for the treatment of infections caused by multi-drug resistant Gram-positive bacteria. In this study, rhodomyrtone was detected within the cell by means of an easy an inexpensive method. The antibacterial effects of rhodomyrtone were investigated on epidemic methicillin-resistant Staphylococcus aureus. Thin-layer chromatography demonstrated the entrapment and accumulation of rhodomyrtone within the bacterial cell wall and cell membrane. The incorporation of radiolabelled precursors revealed that rhodomyrtone inhibited the synthesis of macromolecules including DNA, RNA, proteins, the cell wall, and lipids. Following the treatment with rhodomyrtone at MIC (0.5–1 µg/mL), the synthesis of all macromolecules was significantly inhibited (p ≤ 0.05) after 4 h. Inhibition of macromolecule synthesis was demonstrated after 30 min at a higher concentration of rhodomyrtone (4× MIC), comparable to standard inhibitor compounds. In contrast, rhodomyrtone did not affect lipase activity in staphylococci—both epidemic methicillin-resistant S. aureus and S. aureus ATCC 29213. Interfering with the synthesis of multiple macromolecules is thought to be one of the antibacterial mechanisms of rhodomyrtone.

Antimetastatic Potential of Rhodomyrtone on Human Chondrosarcoma SW1353 Cells

Chondrosarcoma is primary bone cancer, with the forceful capacity to cause local invasion and distant metastasis, and has a poor prognosis. Cancer metastasis is a complication of most cancers; it is one of the leading causes of cancer-related death. Rhodomyrtone is a pure compound that has been shown to induce apoptosis and antimetastasis in skin cancer. However, the inhibitory effect of rhodomyrtone on human chondrosarcoma cell metastasis is largely unknown. Effect of rhodomyrtone on cell viability in SW1353 cell was determined by MTT assay. Antimigration, anti-invasion, and antiadhesion were carried out to investigate the antimetastatic potential of rhodomyrtone on SW1353 cells. Gelatin zymography was performed to determine matrix metalloproteinase-2 (MMP-2) and MMP-9 activities. The effect of rhodomyrtone on the underlying mechanisms was performed by Western blot analysis. The results demonstrated that rhodomyrtone reduced cell viability of SW1353 cells at the low concentration (<3 μg/mL); cell viability was >80%. Rhodomyrtone at the subcytotoxic concentrations (0.5, 1.5, and 3 μg/mL) significantly inhibited cell migration, invasion, and adhesion of SW1353 cells in a dose-dependent fashion. Protein expression of integrin αv, integrin β3, and the downstream migratory proteins including focal adhesion kinase (FAK) and the phosphorylation of serine/threonine AKT, Ras, RhoA, Rac1, and Cdc42 were inhibited after treatment with rhodomyrtone. Moreover, we found that rhodomyrtone decreased the protein level of MMP-2 and MMP-9 as well as the enzyme activity in SW1353 cells. Meanwhile, tissue inhibitor of metalloproteinase-1 (TIMP-1) and TIMP-2 expression was increased in a dose-dependent fashion. Besides, rhodomyrtone dramatically inhibited the expression of growth factor receptor-bound protein-2 (GRB2) and the phosphorylated form of extracellular signal regulation kinase1/2 (ERK1/2) and c-Jun N-terminal kinase1/2 (JNK1/2). These results indicated that rhodomyrtone inhibited SW1353 cell migration, invasion, and metastasis by suppressing integrin αvβ3/FAK/AKT/small Rho GTPases pathway as well as downregulation of MMP-2/9 via ERK and JNK signal inhibition. These findings indicate that rhodomyrtone possessed the antimetastasis activity that may be used for antimetastasis therapy in the future.

Pseudomonas aeruginosa Presents Multiple Vital Changes in Its Proteome in the Presence of 3-Hydroxyphenylacetic Acid, a Promising Antimicrobial Agent

Pseudomonas aeruginosa, a widely distributed opportunistic pathogen, is an important threat to human health for causing serious infections worldwide. Due to its antibiotic resistance and virulence factors, it is so difficult to combat this bacterium; thus, new antimicrobial agents are in search. 3-Hydroxyphenylacetic acid (3-HPAA), which is a phenolic acid mostly found in olive oil wastewater, can be a promising candidate with its dose-dependent antimicrobial properties. Elucidating the molecular mechanism of action is crucial for future examinations and the presentation of 3-HPAA as a new agent. In this study, the antimicrobial activity of 3-HPAA on P. aeruginosa and its action mechanism was investigated via shot-gun proteomics. The data, which are available via ProteomeXchange with identifier PXD016243, were examined by STRING analysis to determine the interaction networks of proteins. KEGG Pathway enrichment analysis via the DAVID bioinformatics tool was also performed to investigate the metabolic pathways that undetected and newly detected groups of the proteins. The results displayed remarkable changes after 3-HPAA exposure in the protein profile of P. aeruginosa related to DNA replication and repair, RNA modifications, ribosomes and proteins, cell envelope, oxidative stress, as well as nutrient availability. 3-HPAA showed its antimicrobial action on P. aeruginosa by affecting multiple bacterial processes; hence, it could be categorized as a multitarget antimicrobial agent.

Antibacterial mechanism of rhodomyrtone involves the disruption of nucleoid segregation checkpoint in Streptococcus suis

Rhodomyrtone has been recently demonstrated to possess a novel antibiotic mechanism of action against Gram-positive bacteria which involved the multiple targets, resulting in the interference of several bacterial biological processes including the cell division. The present study aims to closely look at the downstream effect of rhodomyrtone treatment on nucleoid segregation in Streptococcus suis, an important zoonotic pathogen. The minimum inhibition concentration (MIC) and the minimum bactericidal concentration (MBC) values of rhodomyrtone against the recombinant S. suis ParB-GFP, a nucleoid segregation reporter strain, were 0.5 and 1 µg/ml, respectively, which were equivalent to the potency of vancomycin. Using the fluorescence live-cell imaging, we demonstrated that rhodomyrtone at 2× MIC caused incomplete nucleoid segregation and septum misplacement, leading to the generation of anucleated cells. FtsZ immune-staining of rhodomyrtone-treated S. suis for 30 min revealed that the large amount of FtsZ was trapped in the region of high fluidity membrane and appeared to be able to polymerize to form a complete Z-ring. However, the Z-ring was shifted away from the midcell. Transmission electron microscopy further confirmed the disruption of nucleoid segregation and septum misplacement at 120 min following the rhodomyrtone treatment. Asymmetric septum formation resulted in either generation of minicells without nucleoid, septum formed over incomplete segregated nucleoid (guillotine effect), or formation of multi-constriction of Z-ring within a single cell. This finding spotlights on antibacterial mechanism of rhodomyrtone involves the early stage in bacterial cell division process.

Proteomic profiling unveils citral modulating expression of IsaA, CodY and SaeS to inhibit biofilm and virulence in methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the dangerous human pathogens and it is categorized as a high priority multi-drug resistant bacterium by WHO. Biofilm forming ability of MRSA is responsible for persistent infections and also difficult to eradicate using antibiotic therapy as biofilm is much more resistant to antibiotics. Thus, targeting biofilm and virulence has become an alternative approach to attenuate the pathogenicity of bacterium without affecting the growth. Hence, the present study was aimed at evaluation of antibiofilm potential of citral against MRSA and to decode the possible mode of action. Citral inhibited biofilm formation by MRSA without affecting growth at 100 μg/mL. Microscopic analyses evidenced that citral greatly hampered the surface adherence of MRSA. Effect of citral on cellular proteome of MRSA was studied using two-dimensional gel electrophoresis (2DGE) and differentially regulated proteins were identified using nano LC-MS/MS and MALDI-TOF/TOF analysis. Gene ontology and STRING analysis revealed that citral differentially regulated the proteins involved in pleotropic transcriptional repression (CodY), cell wall homeostasis (IsaA), regulation of exotoxin secretion (SaeS), cell adhesion, hemolysis, capsular polysaccharide biosynthesis and pathogenesis. Gene expression analysis and in vitro assays further validated the alteration in synthesis of slime, hemolysin, lipase, staphyloxanthin and oxidant susceptibility. Thus, the present study unveiled the multiple protein targeted antibiofilm potential of citral and portrays citral as a promising therapeutic agent to combat biofilm mediated MRSA infections with less possibility of resistance development.

The anti-MRSA compound 3-O-alpha-L-(2″,3″-di-p-coumaroyl)rhamnoside (KCR) inhibits protein synthesis in Staphylococcus aureus

Methicillin-resistant S aureus (MRSA) contributes to patient mortality and extended hospital stays. 3-O-alpha-L-(2″,3″-di-p-coumaroyl)rhamnoside (KCR) is a natural product antibiotic that is effective against MRSA but has no known mechanism of action (MOA). We used proteomics to identify the MOA for KCR. Methicillin sensitive S aureus and a mixture of four KCR stereoisomers were tested. A time-kill assay was used to choose a 4 h treatment using KCR at 5× its MIC for proteomic analysis. S aureus was treated in triplicate with KCR, oxacillin or vehicle and quantitative proteomic analysis was carried out using isobaric tags and mass spectrometry. 1190 proteins were identified and 552 were affected by KCR (q < 0.01). Ontology analysis identified 6 distinct translation-related categories that were affected by KCR (PIANO, 10% false-discovery rate) including structural constituent of ribosome, translation, rRNA binding, tRNA binding, tRNA processing and aminoacyl-tRNA ligase activity. Median fold changes (KCR vs Control) for small and large ribosomal components were 1.46 and 1.43 respectively. KCR inhibited the production of luciferase protein in an in vitro assay (IC50 39.6 μg/ml). Upregulation of translation-related proteins in response to KCR indicates that KCR acts to disrupt S aureus protein synthesis. This was confirmed with an in vitro transcription/translation assay. SIGNIFICANCE: Methicillin-resistant S aureus (MRSA) contributes to patient mortality and extended hospital stays. 3-O-alpha-L-(2″,3″-di-p-coumaroyl)rhamnoside (KCR) is a natural product antibiotic that is effective against MRSA but has no known mechanism of action (MOA). Using proteomic analysis we determined that KCR acts by inhibiting protein synthesis. KCR is an exciting novel antibiotic and this work represents an important step in its development towards clinical use.

Inactivation of farR Causes High Rhodomyrtone Resistance and Increased Pathogenicity in Staphylococcus aureus

Rhodomyrtone (Rom) is an acylphloroglucinol antibiotic originally isolated from leaves of Rhodomyrtus tomentosa. Rom targets the bacterial membrane and is active against a wide range of Gram-positive bacteria but the exact mode of action remains obscure. Here we isolated and characterized a spontaneous Rom-resistant mutant from the model strain Staphylococcus aureus HG001 (Rom^R) to learn more about the resistance mechanism. We showed that Rom-resistance is based on a single point mutation in the coding region of farR [regulator of fatty acid (FA) resistance] that causes an amino acid change from Cys to Arg at position 116 in FarR, that affects FarR activity. Comparative transcriptome analysis revealed that mutated farR affects transcription of many genes in distinct pathways. FarR represses for example the expression of its own gene (farR), its flanking gene farE (effector of FA resistance), and other global regulators such as agr and sarA. All these genes were consequently upregulated in the Rom^R clone. Particularly the upregulation of agr and sarA leads to increased expression of virulence genes rendering the Rom^R clone more cytotoxic and more pathogenic in a mouse infection model. The Rom-resistance is largely due to the de-repression of farE. FarE is described as an efflux pump for linoleic and arachidonic acids. We observed an increased release of lipids in the Rom^R clone compared to its parental strain HG001. If farE is deleted in the Rom^R clone, or, if native farR is expressed in the Rom^R strain, the corresponding strains become hypersensitive to Rom. Overall, we show here that the high Rom-resistance is mediated by overexpression of farE in the Rom^R clone, that FarR is an important regulator, and that the point mutation in farR (Rom^R clone) makes the clone hyper-virulent.

A review on medicinal plant extracts and their active ingredients against methicillin-resistant and methicillin-sensitive Staphylococcus aureus

Staphylococcus aureus is among the pathogens capable of developing a broad spectrum of infections in human beings. In addition to the hospital, the bacterium is present in the community and has a high resistance to antibiotics, which is also increasing on an ongoing basis. Resistance to β-lactam antibiotic family is one of the concerns about the bacterium that has encountered the treatment of such infections with difficulty. Due to the increased resistance and importance of this bacterium, new strategies are needed to control this pathogen. One of these approaches is the use of medicinal plants, which has attracted many researchers in the last decade. Several studies have been carried out or are being designed using various herbs to find active ingredients to deal with this bacterium. The aim of this study was to present the antibacterial activity of different medicinal plants and the effects of their active ingredients on methicillin-resistant and methicillin-sensitive S. aureus and to clarify the pathway to further studies in this regard.

The Health Beneficial Properties of Rhodomyrtus tomentosa as Potential Functional Food

Rhodomyrtus tomentosa (Aiton) Hassk. is a flowering plant belonging to the family Myrtaceae, native to southern and southeastern Asia. It has been used in traditional Vietnamese, Chinese, and Malaysian medicine for a long time for the treatment of diarrhea, dysentery, gynecopathy, stomachache, and wound healing. Moreover, R. tomentosa is used to make various food products such as wine, tea, and jam. Notably, R. tomentosa has been known to contain structurally diverse and biologically active metabolites, thus serving as a potential resource for exploring novel functional agents. Up to now, numerous phenolic and terpenoid compounds from the leaves, root, or fruits of R. tomentosa have been identified, and their biological activities such as antioxidant, antibacterial, anti-inflammatory, and anticancer have been evidenced. In this contribution, an overview of R. tomentosa and its health beneficial properties was focused on and emphasized.

Amino acids and proteomic acclimation of Staphylococcus aureus when incubated in a defined minimal medium supplemented with 5% sodium chloride

Staphylococcus aureus is a versatile bacterium that can adapt to survive and grow in a wide range of salt concentrations. This study investigated whether the cells could mount a response to survive a challenge of 5% NaCl in a minimal incubation medium that would not support cell replication. Cells were grown in liquid culture, washed and then incubated for 90 min at 37°C in a medium that contained only glycine and glucose as substrates in PBS plus trace elements. The control cells were compared with a treatment group which was incubated with an additional 5% NaCl. Significantly more glycine was taken up by the cells exposed to 5% NaCl compared with control cells, and both groups consumed 99% of the glucose supplied. The NaCl treated cells had significantly higher cytoplasmic levels of proline and glutamic acid as well as lower levels of alanine and methionine compared with the controls (p < 0.05). The levels of the two major cytoplasmic amino acids, aspartic acid and glycine, remained constant in control and treated cells. Proteomic analyses revealed that 10 proteins showed differential responses between the control and treatment groups. The reductions in proteins were primarily associated with processes of protein biosynthesis, pathogenicity, and cell adhesion. Since cell numbers remained constant during the incubation period in minimal medium, it was concluded that there was no cell division to support population growth. The results provided evidence that the cells in the minimal medium exposed to the NaCl treatment underwent in situ homeostatic changes to adjust to the new environmental conditions. It was proposed that this represented a phenotypic shift to form cells akin to small colony variants, with lower metabolic rates and lower levels of key proteins associated with pathogenicity.

Rhodomyrtosone B, a membrane-targeting anti-MRSA natural acylgphloroglucinol from Rhodomyrtus tomentosa

ETHNOPHARMACOLOGICAL RELEVANCE

The leaves of Rhodomyrtus tomentosa are traditionally used in the treatment of infectious diseases such as wound infections in Chinese traditional medicine. The mechanisms of the activity of rhodomyrtosone B (RDSB), a natural acylphloroglucinol isolated from the leaves of Rhodomyrtus tomentosa, are still not understood. We provided a detailed investigation of the antibacterial action of RDSB against bacteria in vitro and in vivo.

MATERIALS AND METHODS

The antibacterial activity of RDSB was tested by the microdilution method against a panel of bacteria, and a time-killing assay was carried out according to CLSI guidelines. The cytotoxic potential of RDSB was evaluated against mammalian cells, and its haemolytic activity towards rabbit red blood cells (RBCs) was assessed. The mode of action of RDSB was investigated by targeting bacterial membranes, and its resistance was evaluated using a sequential passaging method. The antibacterial activities in vivo were assessed against MRSA in a mouse skin infection mode.

RESULTS

RDSB exhibited distinct antibacterial activities against selected Gram-positive pathogens responsible for serious infections, even including methicillin-resistant Staphylococcus aureus (MRSA) with a minimum inhibitory concentration (MIC) of 0.62-1.25 µg/mL and vancomycin-resistant Enterococcus faecium (VRE) with an MIC of 2.5 µg/mL. RDSB displayed much more rapid bactericidal activity against MRSA than that of vancomycin. The membrane-targeting experiments revealed that RDSB exhibited significant antibacterial activity with the perturbation of bacterial membrane potential and an increase in membrane permeability. In particular, RDSB had weak cytotoxicity to mammalian cells (IC₅₀ >14 µg/mL) and has advantageous specificity against selected Gram-positive bacterial membranes rather than RBCs. Notably, RDSB displayed in vitro antibacterial activities against MRSA without drug-resistance and profoundly attenuated the skin ulcer formation in a murine model of MRSA infection under a single dose of 40 µg RDSB per mouse.

CONCLUSION

RDSB has profound antibacterial activity against drug-resistant bacteria (MRSA and VRE) and low cytotoxicity. It is bactericidal in nature, and an increase in membrane permeability resulting from membrane perturbation is one of its modes of action. RDSB represents a promising natural antibiotic to combat drug-resistant (MRSA and VRE) infections.

Structures and Bioactive Properties of Myrtucommulones and Related Acylphloroglucinols from Myrtaceae

Myrtaceae are a group of plants that include a number of renowned species used in ethnomedicine in many areas worldwide. Their valuable therapeutic properties have stimulated a fruitful research activity addressed to the identification of the bioactive components of their extracts yielding a great diversity of terpenes; polyphenols; and other exclusive products. Among the latter, starting with the discovery of myrtucommulone A from myrtle (Myrtus communis), a series of structurally-related acylphloroglucinol compounds have been characterized from several species that represent the basic active principles to be considered in view of possible drug development. Aspects concerning chemical and biological properties of these products are reviewed in the present paper.

Antibacterial activity of rhodomyrtone on Clostridium difficile vegetative cells and spores in vitro

The increasing incidence and severity of diarrhoea and colitis caused by Clostridium difficile, together with a high rate of relapse following treatment with currently recommended antimicrobials, calls for novel interventions for C. difficile infection (CDI). Rhodomyrtone, a bioactive compound derived from the leaves of the rose myrtle (Rhodomyrtus tomentosa) has demonstrated antibacterial activity against several Gram-positive bacteria. This study compared the in vitro antimicrobial activity of rhodomyrtone on C. difficile with that of vancomycin, a recommended agent for the treatment of CDI. Determination of the minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) of rhodomyrtone and vancomycin for ten C. difficile isolates showed that the MICs of rhodomyrtone for C. difficile vegetative cells (0.625-2.5 mg/L) were comparable with that of vancomycin (1.25 mg/L), but the MBCs of rhodomyrtone (1.25-5 mg/L) were significantly lower than those for vancomycin (5 mg/L to ˃40 mg/L; P < 0.001). Time-kill assays showed rapid bactericidal activity for rhodomyrtone, with ≥99% killing within 4 h. Rhodomyrtone was also four-fold more potent than vancomycin in inhibiting C. difficile spore outgrowth. Transmission electron microscopy of rhodomyrtone-treated C. difficile revealed cell lysis and evidence of defective cell division and spore formation. These studies indicate that rhodomyrtone should be further investigated as a potential treatment for CDI.

Systematically integrated metabonomic-proteomic studies of Escherichia coli under ciprofloxacin stress

Many antibiotics are used to kill pathogenic Escherichia coli each year, resulting in an increase in the number of antibiotic-resistant strains. In this study, an integrated metabonomic-proteomic method was performed to systematically compare the profiles of metabolites and proteins with or without ciprofloxacin (CFLX) treatment. Proteomics identified 290 altered proteins including 143 with decreased and 147 increased expression, respectively. Metabonomics identified 65 altered metabolites including 58 and 7 with decreased and increased expression, respectively. The integrated analysis showed that the CFLX inhibited the DNA replication and increased the expression of DNA gyrase and DNA topoisomerase 1, while causing a sharp decrease in metabolic activity such as the alanine, aspartate and glutamate metabolism. Moreover, CFLX affected the biosynthesis of aminoacyl- transfer RNAs (tRNAs), leading to an increase in aminoacyl-tRNAs ligases, but limited the aminoacyl-tRNAs-mediated-biosynthesis of related amino acids. In this study, we identified the metabolite and protein profiles under CFLX stress, indicating the mode of action of antibiotics in E. coli. Furthermore, the decreasing metabolic activity in E. coli may be an effective strategy to escape killing by antimicrobials or toxic compounds. The results of this study will advance our understanding of the mechanisms underlying the resistance of bacteria to antibiotics.

BIOLOGICAL SIGNIFICANCE

To investigate the biological impact of antibiotics stress on Escherichia coli, we applied an integrated metabonomic-proteomic method to systematically compare the profiles of metabolites and proteins between with and without antibiotics ciprofloxacin (CFLX) treatment. Following bioinformatics analysis showed that CFLX inhibited the DNA replication and increased the expression of DNA gyrase and DNA topoisomerase, while causing a sharp increase in the alanine, aspartate and glutamate metabolism. Moreover, CFLX affected the biosynthesis of tRNAs and limited the generation of related amino acids metabolites. In a summary, our results will provide the metabolite and protein profiles under CFLX stress, indicating the mode of action of antibiotics in E. coli. The results of this study will advance our understanding of the mechanisms underlying the resistance of bacteria to antibiotics.

The novel antibiotic rhodomyrtone traps membrane proteins in vesicles with increased fluidity

The acylphloroglucinol rhodomyrtone is a promising new antibiotic isolated from the rose myrtle Rhodomyrtus tomentosa, a plant used in Asian traditional medicine. While many studies have demonstrated its antibacterial potential in a variety of clinical applications, very little is known about the mechanism of action of rhodomyrtone. Preceding studies have been focused on intracellular targets, but no specific intracellular protein could be confirmed as main target. Using live cell, high-resolution, and electron microscopy we demonstrate that rhodomyrtone causes large membrane invaginations with a dramatic increase in fluidity, which attract a broad range of membrane proteins. Invaginations then form intracellular vesicles, thereby trapping these proteins. Aberrant protein localization impairs several cellular functions, including the respiratory chain and the ATP synthase complex. Being uncharged and devoid of a particular amphipathic structure, rhodomyrtone did not seem to be a typical membrane-inserting molecule. In fact, molecular dynamics simulations showed that instead of inserting into the bilayer, rhodomyrtone transiently binds to phospholipid head groups and causes distortion of lipid packing, providing explanations for membrane fluidization and induction of membrane curvature. Both its transient binding mode and its ability to form protein-trapping membrane vesicles are unique, making it an attractive new antibiotic candidate with a novel mechanism of action.

Bacterial antibiotic resistance constitutes a major public healthcare issue and deaths caused by antimicrobial resistance are expected to soon exceed the number of cancer-related fatalities. In order to fight resistance, new antibiotics have to be developed that are not affected by existing microbial resistance strategies. Thus, antibiotics with novel or multiple targets are urgently needed. Rhodomyrtone displays excellent antibacterial activity, has been safely used in traditional Asian medicine for a long time, and resistance against this promising antibiotic candidate could not be detected in multiple passaging experiments. Here we demonstrate that rhodomyrtone possesses a completely novel mechanism of action, which is opposed to that of existing cell envelope-targeting drugs, minimizing the risk of cross-resistance, and in fact rhodomyrtone is highly active against e.g. vancomycin-resistant Staphylococcus aureus. Thus, rhodomyrtone is an extremely interesting compound for further antibacterial drug development.

Early Effects of Rhodomyrtone on Membrane Integrity in Methicillin-Resistant Staphylococcus aureus

Strong evidence of high potency of rhodomyrtone as a promising antibacterial agent against pathogenic gram-positive bacteria has been clearly demonstrated in our previous work. The aim of this study was to provide insight into early action of rhodomyrtone, an acylphloroglucinol, on membrane damage in multidrug-resistant methicillin-resistant Staphylococcus aureus (MRSA). Early effects of rhodomyrtone on the bacterial membrane integrity were detected in a time-course study. Flow cytometry revealed a reduction in green fluorescent emission and increase in uptake of propidium iodide in rhodomyrtone-treated bacterial cells in a concentration- and time-dependent manner. Disruption of cytoplasmic membrane was further monitored by measuring cellular adenosine triphosphate (ATP) and potassium ion (K⁺). Leakage of both ATP and K⁺ and significant decrease in intracellular ATP in MRSA were observed following treatment. Pronounced changes in the bacterial ultrastructure and morphology were confirmed by transmission electron microscopy and scanning electron microscopy. Bacterial cell disruption, holes in cell surface, and bulge formations were noted in rhodomyrtone-treated cells. In this study, we provided relevant data to clarify that rhodomyrtone is a bacterial cell membrane-damaging agent. A possible early effect of this novel compound involves bacterial membrane disruption.

Antimicrobial constituents of peel and seeds of camu-camu (Myrciaria dubia)

Various antimicrobial constituents of camu-camu fruit were isolated. Acylphloroglucinol (compound 1) and rhodomyrtone (compound 2) were isolated from the peel of camu-camu (Myrciaria dubia) fruit, while two other acylphloroglucinols (compounds 3 and 4) were obtained from camu-camu seeds. The structures of the isolated compounds were characterized by spectrophotometric methods. Compounds 1 and 4 were confirmed to be new acylphloroglucinols with different substituents at the C7 or C9 position of 2, and were named myrciarone A and B, respectively. Compound 3 was determined to be isomyrtucommulone B. This is the first report of the isolation of 3 from a natural resource. The antimicrobial activities of compounds 1, 3, and 4 were similar to those of 2, and the minimum inhibitory concentrations were either similar to or lower than that of kanamycin. These results suggest that the peel and seeds of camu-camu fruit could be utilized for therapeutic applications.

Integrated proteomic and metabolomic analysis reveals that rhodomyrtone reduces the capsule in Streptococcus pneumoniae

The emergence of antibiotic-resistant pathogenic bacteria is a healthcare problem worldwide. We evaluated the antimicrobial activity of rhodomyrtone, an acylphloroglucinol present in Rhodomyrtus tomentosa leaves, against the human Gram-positive pathogen Streptococcus pneumoniae. The compound exhibited pronounced anti-pneumococcal activity against a broad collection of clinical isolates. We studied the effects at the molecular level by integrated proteomic and metabolomic analysis. The results revealed alterations in enzymes and metabolites involved in several metabolic pathways including amino acid biosynthesis, nucleic acid biosynthesis, glucid, and lipid metabolism. Notably, the levels of two enzymes (glycosyltransferase and UTP-glucose-1-phosphate uridylyltransferase) and three metabolites (UDP-glucose, UDP-glucuronic acid and UDP-N-acetyl-D-galactosamine) participating in the synthesis of the pneumococcal capsule clearly diminished in the bacterial cells exposed to rhodomyrtone. Rhodomyrtone-treated pneumococci significantly possessed less amount of capsule, as measured by a colorimetric assay and visualized by electron microscopy. These findings reveal the utility of combining proteomic and metabolomic analyses to provide insight into phenotypic features of S. pneumoniae treated with this potential novel antibiotic. This can lead to an alternative antibiotic for the treatment of S. pneumoniae infections, because of the growing concern regarding antimicrobial resistance.

Rhodomyrtus tomentosa Leaf Extract Inhibits Methicillin-Resistant Staphylococcus aureus Adhesion, Invasion, and Intracellular Survival in Human HaCaT Keratinocytes

Methicillin-resistant Staphylococcus aureus (MRSA) has an ability to invade nonprofessional phagocytic cells, resulting in persistent infections and most likely host cell death. Series of our studies have claimed pronounced antibacterial efficacy of Rhodomyrtus tomentosa leaf extract. This study was to further investigate potency of the extract in intracellular killing of human HaCaT keratinocytes. Pretreatment of MRSA with the extract resulted in a remarkable reduction in the bacterial adhesion to HaCaT keratinocytes, compared with untreated control (p < 0.001). In addition, at least 60% inhibition of the bacterial invasion into HaCaT cells was observed. Intracellular killing assay demonstrated that the extract exhibited strong antibacterial activity against intracellular MRSA at nontoxic concentrations (128 mg/L), which may have resulted from the increase in bactericidal activity under phagolysosomal pH. Transmission electron microscopy displayed the effects of the extract on alterations in the bacterial cell morphology with cell lysis. Fluorescence microscopy revealed that the extract decreased MRSA-induced apoptosis in HaCaT cells. In addition, cytotoxicity of HaCaT cells caused by MRSA supernatant was reduced at least 50% by the extract. The potential activities of R. tomentosa extract may be useful in an alternative treatment of MRSA infections in slight acidic compartments, particularly skin infections.

Proteomic Approach for Extracting Cytoplasmic Proteins from Streptococcus sanguinis using Mass Spectrometry

Streptococcus sanguinis is a commensal and early colonizer of oral cavity as well as an opportunistic pathogen of infectious endocarditis. Extracting the soluble proteome of this bacterium provides deep insights about the physiological dynamic changes under different growth and stress conditions, thus defining "proteomic signatures" as targets for therapeutic intervention. In this protocol, we describe an experimentally verified approach to extract maximal cytoplasmic proteins from Streptococcus sanguinis SK36 strain. A combination of procedures was adopted that broke the thick cell wall barrier and minimized denaturation of the intracellular proteome, using optimized buffers and a sonication step. Extracted proteome was quantitated using Pierce BCA Protein Quantitation assay and protein bands were macroscopically assessed by Coomassie Blue staining. Finally, a high resolution detection of the extracted proteins was conducted through Synapt G2Si mass spectrometer, followed by label-free relative quantification via Progenesis QI. In conclusion, this pipeline for proteomic extraction and analysis of soluble proteins provides a fundamental tool in deciphering the biological complexity of Streptococcus sanguinis.

Effects of rhodomyrtone on Gram-positive bacterial tubulin homologue FtsZ

Rhodomyrtone, a natural antimicrobial compound, displays potent activity against many Gram-positive pathogenic bacteria, comparable to last-defence antibiotics including vancomycin and daptomycin. Our previous studies pointed towards effects of rhodomyrtone on the bacterial membrane and cell wall. In addition, a recent molecular docking study suggested that the compound could competitively bind to the main bacterial cell division protein FtsZ. In this study, we applied a computational approach (in silico), in vitro, and in vivo experiments to investigate molecular interactions of rhodomyrtone with FtsZ. Using molecular simulation, FtsZ conformational changes were observed in both (S)- and (R)-rhodomyrtone binding states, compared with the three natural states of FtsZ (ligand-free, GDP-, and GTP-binding states). Calculations of free binding energy showed a higher affinity of FtsZ to (S)-rhodomyrtone (−35.92 ± 0.36 kcal mol⁻¹) than the GDP substrate (−23.47 ± 0.25 kcal mol⁻¹) while less affinity was observed in the case of (R)-rhodomyrtone (−18.11 ± 0.11 kcal mol⁻¹). In vitro experiments further revealed that rhodomyrtone reduced FtsZ polymerization by 36% and inhibited GTPase activity by up to 45%. However, the compound had no effect on FtsZ localization in Bacillus subtilis at inhibitory concentrations and cells also did not elongate after treatment. Higher concentrations of rhodomyrtone did affect localization of FtsZ and also affected localization of its membrane anchor proteins FtsA and SepF, showing that the compound did not specifically inhibit FtsZ but rather impaired multiple divisome proteins. Furthermore, a number of cells adopted a bean-like shape suggesting that rhodomyrtone possibly possesses further targets involved in cell envelope synthesis and/or maintenance.

Anti-metastatic effect of rhodomyrtone from Rhodomyrtus tomentosa on human skin cancer cells

This study focused on the inhibitory effect of rhodomyrtone, a bioactive compound isolated from the leaves of Rhodomyrtus tomentosa (Aiton) Hassk., on cancer metastasis in epidermoid carcinoma A431 cells and on the verification of the underlying related molecular mechanisms of this event. We demonstrated that rhodomyrtone at the subcytotoxic concentration (0.5 and 1.5 µg/ml) exhibited pronounced inhibition of cancer metastasis by reducing cell migration, cell adhesive ability and cell invasion of A431 cells in a dose-dependent manner. Data demonstrated that rhodomyrtone could inhibit the focal adhesion kinase (FAK) and phosphorylation of protein kinase B (AKT), c-Raf, extracellular signal-regulated kinase 1/2 (ERK1/2) and p38 MAPK involved in the downregulation the enzyme activities and protein expression of matrix metalloproteinase-2 (MMP-2) and MMP-9. Moreover, we found that rhodomyrtone increased the expression of TIMP-1 and TIMP-2, which are inhibitors of MMP-9 and MMP-2, respectively. Rhodomyrtone also inhibited the expression of NF-κB and phosphorylation of NF-κB in a dose-dependent manner. These results suggested that rhodomyrtone inhibited A431 cell metastasis by reducing MMP-2/9 activities and expression through inhibiting ERK1/2, p38 and FAK/Akt signaling pathways via NF-κB activities. This finding suggested that rhodomyrtone may be a novel antimetastasis agent for treatment of skin cancer cells.

Comparative Proteomic Analysis of Differential Proteins in Response to Aqueous Extract of Quercus infectoria Gall in Methicillin-Resistant Staphylococcus aureus

The aim of this study is to analyze the differential proteins in MRSA ATCC 33591 treated with aqueous extract from Q. infectoria gall. Protein extracts were obtained from MRSA cells by sonication and were separated by 2D polyacrylamide gels. Protein spots of interest were extracted from the gels and identified using LC-ESI-QTOF MS. The concentration of Q. infectoria extract used for 2D-gel electrophoresis was subinhibitory concentration. Minimum inhibitory concentration (MIC) value of the extract against MRSA was 19.50 μg/mL with bacteriostatic action at 1x MIC from time-kill assay. However, the extract exhibited dose-dependent manner and was bactericidal at 4x MIC with more than 3 log10 CFU/mL reduction at 4 h. 2D-GE map showed that 18 protein spots were upregulated and another six were downregulated more than twofold (p < 0.05) after treatment with subinhibitory concentration. Out of six proteins being downregulated, four proteins were identified as ferritin and catalase, branched-chain alpha-keto acid dehydrogenase subunit E2, and succinyl-CoA ligase [ADP-forming] subunit beta. Seven upregulated proteins which have been successfully identified were 3-hydroxyacyl-CoA dehydrogenase, NAD binding domain protein, formate C-acetyltransferase, 3-hydroxyacyl-[acyl-carrier-protein] dehydratase FabZ, NAD dependent epimerase/dehydratase family protein, and phosphopantothenoyl cysteine decarboxylase. It is postulated that the main mechanism of aqueous extract from gall of Q. infectoria was most likely involved in energy metabolism and protein stress.

Antibacterial mechanism of daptomycin antibiotic against Staphylococcus aureus based on a quantitative bacterial proteome analysis

Daptomycin (DAP) is a novel lipopeptide antibiotic which exhibits excellent antibacterial activity against most clinically relevant Gram-positive bacteria, but the DAP-targeting protein molecules against host bacterial infection are far from clear. In order to discover bacterial protein response to DAP treatment, an iTRAQ-based quantitative proteomic analysis was applied to identify differential bacterial proteome profiling of Staphylococcus aureus (S. aureus) ATCC 25923 to 0.125μg/ml DAP exposure. Totally 51 bacterial proteins were significantly changed with DAP treatment, among which 34 proteins were obviously up-regulated and 17 proteins were down-regulated. Meanwhile, 139 bacterial cell membrane (CM) proteins were identified, and 7 CM proteins were significantly altered to decrease CM potential to disrupt bacterial cell membrane. Especially the up-regulation of NDK and down-regulation of NT5 in several S. aureus strains are validated to be a universal variation tendency response to DAP treatment. Under DAP exposure, bacterial membrane potential is decreased and cell membrane is disrupted, and bacterial chromosome is aggregated, which contributes to bacterial DNA rapid release and induces bacteria death within 2-5h. In general, multiple bacterial protein expressions are changed in response to DAP antibiotic exposure, which disrupts host bacterial physiology by multiple cellular levels. To our knowledge, this is the first time to exactly identify infectious bacterial proteins in response to DAP antibiotic action. Our findings help better understand DAP antibacterial mechanism and develop novel DAP derivatives against the upcoming antibiotic-resistant bacterial infection.

BIOLOGICAL SIGNIFICANCE

DAP is a novel lipopeptide antibiotic that it exhibits excellent in vitro activity against most clinically relevant Gram-positive bacteria, and the investigations on its pharmaceutical action mode of DAP have dramatically increased in the past decade due to its unique antimicrobial mechanism. However, the target molecules of DAP acting on the infectious bacteria, are far from clear. The state-of-the-art quantitative proteomic technologies provide new avenues to uncover underlying mechanism of antibiotics. Our research main aims to identify bacterial proteome profiling of host strain S. aureus response to DAP treatment through an iTRAQ-based quantitative proteomic analysis, which contributes to understand DAP efficient antibacterial activity and the microbial-antibiotic interactions.

Application of Omics Technologies for Evaluation of Antibacterial Mechanisms of Action of Plant-Derived Products

In the face of increasing bacterial resistance to antibiotics currently in use, the search for new antimicrobial agents has received a boost in recent years, with natural products playing an important role in this field. In fact, several methods have been proposed to investigate the antibacterial activities of natural products. However, given that the ultimate aim is future therapeutic use as novel drugs, it is extremely necessary to elucidate their modes of action, stating the molecular effects in detail, and identifying their targets in the bacterial cell. This review analyzes the application of “omics technologies” to understand the antibacterial mechanisms of bioactive natural products, to stimulate research interest in this area and promote scientific collaborations. Some studies have been specifically highlighted herein by examining their procedures and results (targeted proteins and metabolic pathways). These approaches have the potential to provide new insights into our comprehension of antimicrobial resistance/susceptibility, creating new perspectives for the struggle against bacteria, and leading to the development of novel products in the future.

New Is Old, and Old Is New: Recent Advances in Antibiotic-Based, Antibiotic-Free and Ethnomedical Treatments against Methicillin-Resistant Staphylococcus aureus Wound Infections

Staphylococcus aureus is the most common pathogen of wound infections. Thus far, methicillin-resistant S. aureus (MRSA) has become the major causative agent in wound infections, especially for nosocomial infections. MRSA infections are seldom eradicated by routine antimicrobial therapies. More concerning, some strains have become resistant to the newest antibiotics of last resort. Furthermore, horizontal transfer of a polymyxin resistance gene, mcr-1, has been identified in Enterobacteriaceae, by which resistance to the last group of antibiotics will likely spread rapidly. The worst-case scenario, "a return to the pre-antibiotic era", is likely in sight. A perpetual goal for antibiotic research is the discovery of an antibiotic that lacks resistance potential, such as the recent discovery of teixobactin. However, when considering the issue from an ecological and evolutionary standpoint, it is evident that it is insufficient to solve the antibiotic dilemma through the use of antibiotics themselves. In this review, we summarized recent advances in antibiotic-based, antibiotic-free and ethnomedical treatments against MRSA wound infections to identify new clues to solve the antibiotic dilemma. One potential solution is to use ethnomedical drugs topically. Some ethnomedical drugs have been demonstrated to be effective antimicrobials against MRSA. A decline in antibiotic resistance can therefore be expected, as has been demonstrated when antibiotic-free treatments were used to limit the use of antibiotics. It is also anticipated that these drugs will have low resistance potential, although there is only minimal evidence to support this claim to date. More clinical trials and animal tests should be conducted on this topic.

Divergent Total Syntheses of Rhodomyrtosones A and B

Herein, we report total syntheses of the tetramethyldihydroxanthene natural product rhodomyrtosone B and the related bis-furan β-triketone natural product rhodomyrtosone A. Nickel-(II)-catalyzed 1,4-conjugate addition of an α-alkylidene-β-dicarbonyl substrate was developed to access the congener rhodomyrtosone B, and oxygenation of the same monoalkylidene derivative followed by cyclization was employed to obtain the bis-furan natural product rhodomyrtosone A.

Rhodomentones A and B, novel meroterpenoids with unique NMR characteristics from Rhodomyrtus tomentosa

Two novel meroterpenoids were isolated from Rhodomyrtus tomentosa. Their structures with unique NMR characteristics were determined by extensive spectroscopic analysis, single-crystal X-ray diffraction, quantum molecular calculation, chemical transformation as well as total synthesis.

Effects of Rhodomyrtus tomentosa Leaf Extract on Staphylococcal Adhesion and Invasion in Bovine Udder Epidermal Tissue Model

Bovine mastitis is one of the most important infectious diseases in dairy herds, and staphylococci are the most important etiologic agents of this disease. Antibiotics and chemical agents used in livestock for prevention and cure of the disease can accumulate in milk and give rise to food safety concerns. Rhodomyrtus tomentosa leaf extract was studied as an alternative approach to reduce the bacterial infections. The ethanolic extract of this plant demonstrated antibacterial activity with minimum inhibitory concentration (MIC) values as low as 16–64 μg/mL against staphylococcal isolates. In addition, the extract had an effect on the bacterial cell surface properties by increasing its hydrophobicity in a concentration dependent manner. To further extend the antibacterial efficacy, silver nanoparticles synthesized with the extract, a pure rhodomyrtone, and liposomal encapsulated rhodomyrtone were applied and their inhibitory effects on bacterial adhesion and invasion were determined by ex vivo study in a bovine udder epidermal tissue model. These agents exerted remarkable antibacterial activity against staphylococci and decreased the adhesion of the bacterial cells to the tissues. These results supported that R. tomentosa ethanolic extract could be applied as an alternative agent for bovine udder care in dairy farms.

Potential Bio-Control Agent from Rhodomyrtus tomentosa against Listeria monocytogenes

Listeria monocytogenes is an important foodborne pathogen implicated in many outbreaks of listeriosis. This study aimed at screening for the potential use of Rhodomyrtus tomentosa ethanolic leaf extract as a bio-control agent against L. monocytogenes. Twenty-two L. monocytogenes isolates were checked with 16 commercial antibiotics and isolates displayed resistance to 10 antibiotics. All the tested isolates were sensitive to the extract with inhibition zones ranging from 14 to 16 mm. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values ranged from 16 to 32 µg/mL and 128 to 512 µg/mL, respectively. Time-kill assay showed that the extract had remarkable bactericidal effects on L. monocytogenes. The extract at a concentration of 16 µg/mL reduced tolerance to 10% NaCl in L. monocytogenes in 4 h. Stationary phase L. monocytogenes cells were rapidly inactivated by greater than 3-log units within 30 min of contact time with R. tomentosa extract at 128 µg/mL. Electron microscopy revealed fragmentary bacteria with changes in the physical and morphological properties. Our study demonstrates the potential of the extract for further development into a bio-control agent in food to prevent the incidence of L. monocytogenes contamination.

Metabolomic and proteomic responses of Staphylococcus aureus to prolonged cold stress

The high pathogenicity of Staphylococcus aureus is thought to be due to its extraordinary capacity to rapidly adapt to changes in environmental conditions. This study was carried out to investigate whether the cytoplasmic profiles of metabolites and proteins of S. aureus were altered in response to prolonged exposure to cold stress. Metabolic profiling and proteomics were used to characterise alterations in cytoplasmic proteins and metabolites in cells from the mid-exponential phase of growth under ideal conditions at 37°C and compared with equivalent cells exposed to prolonged cold stress for 2 weeks at 4°C. Principle component analysis (PCA) of the metabolomic and proteomic data indicated that, at the mid-exponential phase of growth, prolonged cold stress conditions generated cells with different metabolite and protein profiles compared with those grown at 37°C. Nine ribosomal proteins and citric acid were substantially elevated in the cytoplasmic fractions from the cells adapted to cold-stress but most amino acids showed a reduction in their concentration in cold-stressed samples. The data provided strong evidence supporting the hypothesis that specific changes in metabolic homeostasis and protein composition were critical to the adaptive processes required for survival under cold stress.

BIOLOGICAL SIGNIFICANCE

Work in our laboratory has shown that prolonged exposure of S. aureus to cold stress can result in the formation of small colony variants (SCVs) associated with significant alterations in the cell wall composition. Further studies revealed that S. aureus altered cell size and cell wall thickness in response to exposure to cold temperatures, alterations in pH and exposure to antibiotics. The current study has utilised the prolonged exposure to cold stress as a model system to explore changes in the proteome and associated metabolic homeostasis following environmental challenges. The study provides an improved understanding of how S. aureus adapts to the changing environment whilst in transition between human hosts. The results indicated an unexpected production of 9 ribosomal proteins and citric acid in response to cold stress suggesting specific survival roles for these proteins and citric acid as an adaptation mechanism for empowering survival under these conditions.

An integrated quantitative and targeted proteomics reveals fitness mechanisms of Aeromonas hydrophila under oxytetracycline stress

To date, above ten thousand tons of antibiotics are used in aquaculture each year that lead to the deterioration of natural resources. However, knowledge is limited on the molecular biological behavior of common aquatic pathogens against antibiotics stress. In this study, proteomics profiles of Aeromonas hydrophila, which were exposed to different levels of oxytetracycline (OXY) stress, were displayed and compared using iTRAQ labeling and SWATH-MS based LC-MS/MS methods. A total 1383 proteins were identified by SWATH-MS method, and 2779 proteins were identified from iTRAQ labeling samples. There are 152 up-regulated and 52 down-regulated proteins overlapped in 5 μg/mL OXY stress and both 83 up- and down-regulated proteins overlapped in 10 μg/mL OXY stress in both methods, respectively. Results show that many protein synthesis and translation related proteins increased, while energy generation related proteins decreased in OXY stress. The varieties of selected proteins involved in both pathways were further validated by sMRM(HR), q-PCR, and enzyme activity assay. Furthermore, the concentrations of NAD+ and NADH were measured to verify the characteristic of energy generation process in OXY stress and OXY resistance strain. We demonstrate that the down-regulation of energy generation related metabolic pathways and up-regulation of translation may play an important role in antibiotics fitness or resistance of aquatic pathogens.

In vitro and in vivo evaluation of vancomycin-loaded PMMA cement in combination with ultrasound and microbubbles-mediated ultrasound

Ultrasound (US) has been used to increase elution of antibiotic from an antibiotic-loaded poly(methyl methacrylate) (PMMA) bone cement (ALBC). We aimed to further investigate whether microbubbles-mediated US (US + MB) facilitate elution of vancomycin (VAN) from cylindrical specimens and enhance the activity of the eluted antibiotic against Staphylococcus aureus (S. aureus) in vitro. The study groups comprised cylindrical bone cement fabricated with VAN (VAN), ALBC using US (VAN + US), and ALBC using MB-mediated US (VAN + US + MB). We also carried out an in vivo study involving the activity of VAN from cylindrical cement implanted in tibiae of New Zealand white rabbits inoculated with S. aureus. We found that (1) in vitro, elution from VAN + US + MB cylinders was significantly higher than from either the VAN or VAN + US specimens; (2) the activity of the eluted VAN from the VAN + US + MB cylinders against planktonic S. aureus was significantly higher than from either the control or VAN or VAN + US specimens; and (3) in the rabbits, the activity of the eluted VAN from the VAN + US + MB cylinders against S. aureus was significantly higher than from either the control or VAN or VAN + US specimens. The present results suggest that VAN-loaded PMMA cement irradiated with MB-mediated US may have a role in controlling prosthetic joint infection.

Quercetin 3-O-rutinoside mediated inhibition of PBP2a: computational and experimental evidence to its anti-MRSA activity

The PBP2a is a cell wall synthesizing protein, which causes resistivity in methicillin resistant Staphylococcus aureus (MRSA) from β-lactam antibiotics but it is susceptible to 5th generation cephalosporin, ceftobiprole. Ceftobiprole inhibits the growth of MRSA by targeting the PBP2a-mediated cell wall synthesis, but it is reported to have adverse side effects. Due to this, there is a constant need to develop natural alternatives, which are generally free from adverse side effects. Hence in this study, in silico based docking analysis was performed with 37 quercetin derivatives towards PBP2a inhibition and their efficiencies were compared with β-lactam antibiotic, ceftobiprole. The docking studies suggested that quercetin 3-O-rutinoside (ZINC5280805) interacted efficiently with PBP2a, attaining the highest LibDock score (187.32) compared to other quercetin derivatives. The structural stability and dynamics of the identified lead with PBP2a were validated through molecular dynamics simulation. Simulation results such as RMSD, RMSF, and Rg values indicated that the stability of quercetin 3-O-rutinoside with PBP2a was better, with respect to the un-ligated PBP2a. Furthermore, the quercetin 3-O-rutinoside was subjected to an antibacterial susceptibility test and found to have antibacterial activity at 500, 700, and 900 μM concentration. Also, morphological changes in the bacterial colony and bacterial surface were observed using a scanning electron microscope, when MRSA was treated with 900 μM concentration of quercetin 3-O-rutinoside. Collectively, results from this study suggest that the quercetin 3-O-rutinoside has the capability to inhibit PBP2a and hence could be used as an alternative or in combination with other drugs in treating MRSA infection.

Inhibition of microbial adhesion to plastic surface and human buccal epithelial cells by Rhodomyrtus tomentosa leaf extract

OBJECTIVE

The adherence of oral pathogenic microorganisms to host tissues is the initial step for successful process of oral diseases. This study aimed to determine the effect of the Rhodomyrtus tomentosa leaf extract and rhodomyrtone, an antibacterial compound from R. tomentosa leaf, on adhesion of some oral pathogens to polystyrene plastic surface and human buccal epithelial cells.

METHODS

The minimum inhibitory concentration (MIC) was evaluated using broth microdilution method. The microbial adhesion to the plastic surface and buccal cells was determined using microtiter plate method and microscopy technique.

RESULTS

The ethanol extract of leaf demonstrated antibacterial activity against oral microorganisms including Staphylococcus aureus ATCC 25923, Streptococcus mutans (clinical isolate), and Candida albicans ATCC 90028 with the MIC values of 31.25, 15.62, and 1000μg/ml, respectively. Rhodomyrtone displayed activity with the MIC values of 0.78 and 0.39μg/ml against S. aureus ATCC 25923 and S. mutans, respectively. The MIC value of the compound against C. albicans ATCC 90028 was more than 100μg/ml which was the highest test concentration. All pathogenic microorganisms treated with the extract and rhodomyrtone at their subinhibitory concentrations resulted in a decrease in their adherence ability to both plastic surface and buccal cells.

CONCLUSION

It is suggested that R. tomentosa extract and rhodomyrtone may be useful in therapy or as prophylaxis in infections involving oral pathogens.