Nature-inspired synthesis of antibacterial glucovanillin derivatives.

The ongoing threat of Antimicrobial Resistance (AMR) complicated by the rise of Multidrug-Resistant (MDR) pathogens calls for increased efforts in the search for novel treatment options. While deriving inspiration from antibacterial natural compounds, this study aimed at using synthetic approaches to generate a series of glucovanillin derivatives and explore their antibacterial potentials. Among the synthesized derivatives, optimum antibacterial activities were exhibited by those containing 2,4- and 3,5-dichlorophenylamino group coupled to a glucovanillin moiety (compounds 6h and 8d respectively). In those compounds, the Minimum Inhibitory Concentrations (MIC) of 128-256 µg/mL were observed against reference and MDR strains of Klebsiella pneumoniae, Methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus faecium (VRE). Moreover, these findings emphasize the claims from previous reports on the essence of smaller molecular size, the presence of protonatable amino groups and halogens in potential antibacterial agents. The observed moderate and broad-spectrum activities of the stated derivatives point to their suitability as potential leads towards further efforts to improve their antibacterial activities.

Isolation and Characterization of Galloylglucoses Effective against Multidrug-Resistant Strains of Escherichia coli and Klebsiella pneumoniae.

The search for new antibiotics against multidrug-resistant (MDR), Gram-negative bacteria is crucial with respect to filling the antibiotics development pipeline, which is subject to a critical shortage of novel molecules. Screening of natural products is a promising approach for identifying antimicrobial compounds hosting a higher degree of novelty. Here, we report the isolation and characterization of four galloylglucoses active against different MDR strains of Escherichia coli and Klebsiella pneumoniae. A crude acetone extract was prepared from Paeonia officinalis Linnaeus leaves, and bioautography-guided isolation of active compounds from the extract was performed by liquid-liquid extraction, as well as open column, flash, and preparative chromatographic methods. Isolated active compounds were characterized and elucidated by a combination of spectroscopic and spectrometric techniques. In vitro antimicrobial susceptibility testing was carried out on E. coli and K. pneumoniae using 2 reference strains and 13 strains hosting a wide range of MDR phenotypes. Furthermore, in vivo antibacterial activities were assessed using Galleria mellonella larvae, and compounds 1,2,3,4,6-penta-O-galloyl-ß-d-glucose, 3-O-digalloyl-1,2,4,6-tetra-O-galloyl-ß-d-glucose, 6-O-digalloyl-1,2,3,4-tetra-O-galloyl-ß-d-glucose, and 3,6-bis-O-digalloyl-1,2,4-tri-O-galloyl-ß-d-glucose were isolated and characterized. They showed minimum inhibitory concentration (MIC) values in the range of 2-256 µg/mL across tested bacterial strains. These findings have added to the number of known galloylglucoses from P. officinalis and highlight their potential against MDR Gram-negative bacteria.

Reproducibility challenges in the search for antibacterial compounds from nature.

BACKGROUND: Reproducibility of reported antibacterial activities of plant extracts has long remained questionable. Although plant-related factors should be well considered in serious pharmacognostic research, they are often not addressed in many research papers. Here we highlight the challenges in reproducing antibacterial activities of plant extracts. METHODS: Plants with reported antibacterial activities of interest were obtained from a literature review. Antibacterial activities against Escherichia coli and Klebsiella pneumoniae were tested using extracts' solutions in 10% DMSO and acetone. Compositions of working solutions from both solvents were established using LC-MS analysis. Moreover, the availability of details likely to affect reproducibility was evaluated in articles which reported antibacterial activities of studied plants. RESULTS: Inhibition of bacterial growth at MIC of 256-1024 µg/mL was observed in only 15.4% of identical plant species. These values were 4-16-fold higher than those reported earlier. Further, 18.2% of related plant species had MICs of 128-256 µg/mL. Besides, 29.2% and 95.8% of the extracts were soluble to sparingly soluble in 10% DMSO and acetone, respectively. Extracts' solutions in both solvents showed similar qualitative compositions, with differing quantities of corresponding phytochemicals. Details regarding seasons and growth state at collection were missing in 65% and 95% of evaluated articles, respectively. Likewise, solvents used to dissolve the extracts were lacking in 30% of the articles, whereas 40% of them used unidentified bacterial isolates. CONCLUSION: Reproducibility of previously reported activities from plants' extracts is a multi-factorial aspect. Thus, collective approaches are necessary in addressing the highlighted challenges.

Influence of salt type and ionic strength on self-assembly of dextran sulfate-ciprofloxacin nanoplexes.

We evaluated an analytical setup to identify optimal preparation conditions for nanoplex formation of small molecule drugs and polyelectrolytes using ciprofloxacin (CIP) and dextran sulfate (DS) as model compounds. The suitability of isothermal titration calorimetry (ITC) as a screening tool for rational formulation optimization was assessed. Besides ITC, static and dynamic light scattering, zeta potential measurements and scanning electron microscopy were applied to analyze the influence of different salt types and ionic strengths on CIP/DS nanoplex formation. The addition of low amounts of salt, especially 0.1M NaCl, improved the formation of CIP/DS nanoplexes. The presence of low amounts of salt led to smaller and more numerous particles of higher uniformity but had no influence on the release of CIP from nanoplexes. Furthermore, the molar range, within which efficient complexation was achieved, was broader in the presence of 0.1M NaCl than in the absence of salt with overall comparable complexation efficiency. Importantly, binding affinity correlated with particle shape and morphology, potentially enabling optimization of critical quality attributes based on ITC data. Altogether, ITC along with supplemental methods is a versatile screening tool for the evaluation of nanoplex formulation conditions regarding mixing ratio, salt type and ionic strength.

Bioluminescence and 19F magnetic resonance imaging visualize the efficacy of lysostaphin alone and in combination with oxacillin against Staphylococcus aureus in murine thigh and catheter-associated infection models.

Staphylococci are the leading cause of hospital-acquired infections worldwide. Increasingly, they resist antibiotic treatment owing to the development of multiple antibiotic resistance mechanisms in most strains. Therefore, the activity and efficacy of recombinant lysostaphin as a drug against this pathogen have been evaluated. Lysostaphin exerts high levels of activity against antibiotic-resistant strains of Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA). The therapeutic value of lysostaphin has been analyzed in two different clinically relevant in vivo models, a catheter-associated infection model and a thigh infection model. We infected mice with luciferase-expressing S. aureus Xen 29, and the efficacies of lysostaphin, vancomycin, oxacillin, and combined lysostaphin-oxacillin were investigated by determining numbers of CFU, detecting bioluminescent signals, and measuring the accumulation of perfluorocarbon emulsion at the site of infection by (19)F magnetic resonance imaging. Lysostaphin treatment significantly reduced the bacterial burden in infected thigh muscles and, after systemic spreading from the catheter, in inner organs. The efficiency of lysostaphin treatment was even more pronounced in combinatorial therapy with oxacillin. These results suggest that recombinant lysostaphin may have potential as an anti-S. aureus drug worthy of further clinical development. In addition, both imaging technologies demonstrated efficacy patterns similar to that of CFU determination, although they proved to be less sensitive. Nonetheless, they served as powerful tools to provide additional information about the course and gravity of infection in a noninvasive manner, possibly allowing a reduction in the number of animals needed for research evaluation of new antibiotics in future studies.

Immunotherapeutic strategies to combat staphylococcal infections.

Antibiotic-resistant staphylococci are the leading cause of nosocomial infections in many hospitals around the world. Meanwhile, methicillin-resistant Staphylococcus aureus (MRSA) spread also in the community where highly virulent strains infect healthy adults that have no predisposing risk factors. Although a few novel antibiotics have been recently introduced into clinical practice, the search for alternative strategies to efficiently combat staphylococcal infections is urgently demanded to decrease the enormous burden caused by pathogenic staphylococci. In particular, immunological strategies based on vaccine development or therapeutic antibodies may significantly enhance the efficiency of anti-staphylococcal therapy. Most approaches are directed against surface components of staphylococci such as cell wall-linked adhesins, teichoic acids, capsule, the biofilm component PIA/PNAG, or soluble virulence determinants such as alpha-toxin, Panton-Valentine leukocidin, or superantigenic enterotoxins. Although 2 recent clinical trials have failed, several novel promising vaccines and therapeutic antibodies are currently in preclinical and clinical development.