(Some) current concepts in antibacterial drug discovery

Naturally Occurring Organohalogen Compounds-A Comprehensive Review

The present volume is the third in a trilogy that documents naturally occurring organohalogen compounds, bringing the total number-from fewer than 25 in 1968-to approximately 8000 compounds to date. Nearly all of these natural products contain chlorine or bromine, with a few containing iodine and, fewer still, fluorine. Produced by ubiquitous marine (algae, sponges, corals, bryozoa, nudibranchs, fungi, bacteria) and terrestrial organisms (plants, fungi, bacteria, insects, higher animals) and universal abiotic processes (volcanos, forest fires, geothermal events), organohalogens pervade the global ecosystem. Newly identified extraterrestrial sources are also documented. In addition to chemical structures, biological activity, biohalogenation, biodegradation, natural function, and future outlook are presented.

Optimizing the Culture Medium of Lasiodiplodia sp. to Improve the Yield of Ethyl Acetate Extract as an Antimicrobial Source

Endophytes often inhabit plant tissues and cause no disease symptoms. Lasiodiplodia is generally considered a pathogenic fungus, but such a genus is capable of producing high-value bioactive molecules, such as enzymes, secondary metabolites including antimicrobials. Therefore, Lasiodiplodia sp. endophyte was cultivated in static mode for 12 days and EtOAc extracts were obtained and evaluated against pathogens afterward. Fermentation parameters (glucose, sucrose and NaNO₃) were optimized by the factorial design and response surface methodology, as these are powerful tools to provide reliable information about fungal culture conditions and EtOAc extract yields were considered as response variables. Lasiodiplodia growth curve indicated that optimal production of EtOAc extract mass was achieved after 12 days of fermentation (284 mg 300 mL^-1 broth), which is in agreement with values obtained from validation tests. Minimum Inhibitory Concentration (MIC) and Minimum Microbicidal Concentration (MMC) essays suggested that the endophyte produce substances presenting antimicrobial and antifungal activities against ATCC Staphylococcus aureus and Candida albicans strains at optimum point under evaluated conditions. MIC values ranged between 50 and 100 µg mL^-1 for both pathogens, while MMC of C. albicans ranged from 100 to 200 µg mL^-1, which evidence its fungicidal effect. Furthermore, it was found that the EtOAc extract yield can be increased by optimizing carbon and nitrogen sources in endophyte cultivation, and there was good agreement between predicted and experimental values under optimized conditions. Thus, Lasiodiplodia fungi are promising sources of antimicrobials and changes in carbon and nitrogen sources can improve the yield of secondary metabolites according to the factorial design.

Antibacterial, antibiofilm, anti-inflammatory, and wound healing effects of nanoscale multifunctional cationic alternating copolymers

Infectious diseases caused by new or unknown bacteria and viruses, such as anthrax, cholera, tuberculosis and even COVID-19, are a major threat to humanity. Thus, the development of new synthetic compounds with efficient antimicrobial activity is a necessity. Herein, rationally designed novel multifunctional cationic alternating copolymers were directly synthesized through a step-growth polymerization reaction using a bivalent electrophilic cross-linker containing disulfide bonds and a diamine heterocyclic ring. To optimize the activity of these alternating copolymers, several different diamines and cross-linkers were explored to find the highest antibacterial effects. The synthesized nanopolymers not only displayed good to excellent antibacterial activity as judged by minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against Staphylococcus aureus, Enterococcus faecalis, Pseudomonas aeruginosa, and Escherichia coli, but also reduced the number of biofilm cells even at low concentrations, without killing mammalian cells. Furthermore, in vivo experiments using infected burn wounds in mice demonstrated good antibacterial activity and stimulated wound healing, without causing systemic inflammation. These findings suggest that the multifunctional cationic nanopolymers have potential as a novel antibacterial agent for eradication of multidrug resistant bacterial infections.

Treatment of municipal wastewater by employing membrane bioreactors combined with efficient nitration microbial communities isolated by Isolation Chip with Plate Streaking technology

In this research, we developed a method so-called Isolation Chip with Plate Streaking (ICPS) to selectively enrich nitrifying microbial consortium for treating municipal wastewater. In batch experiment, these bacterial communities were able to remove NH₃ -N in 72 h with an efficiency of 96%. Firmicutes, Bacteroidetes, and Proteobacteria species are dominant bacteria in these communities. When the bacterial communities were used in the membrane bioreactor under typical condition, the removal efficiency was 81.0%. In contrast, under the actual wastewater condition, the efficiency could reach 91.2%. All above results showed clearly that the consortium selected by our ICPS method could achieve high-efficient NH₃ -N removal, thus offering a reliable technique for screening functional microorganisms in the field of water treatment. PRACTITIONER POINTS: ICPS technology was designed and used for screening specialized NH₃ -N-removing isolates. The screening process benefited the growth of the dominant nitrifying bacteria Firmicutes and Bacteroidetes. When the functional bacteria applied into the MBR, the NH₃ -N removal efficiency was 91.2% under actual wastewater conditions.

Natural brominated phenoxyphenols kill persistent and biofilm-incorporated cells of MRSA and other pathogenic bacteria

Due to a high unresponsiveness to chemotherapy, biofilm formation is an important medical problem that frequently occurs during infection with many bacterial pathogens. In this study, the marine sponge-derived natural compounds 4,6-dibromo-2-(2',4'-dibromophenoxy)phenol and 3,4,6-tribromo-2-(2',4'-dibromophenoxy)phenol were found to exhibit broad antibacterial activity against medically relevant gram-positive and gram-negative pathogens. The compounds were not only bactericidal against both replicating and stationary phase-persistent planktonic cells of methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa; they also killed biofilm-incorporated cells of both species while not affecting biofilm structural integrity. Moreover, these compounds were active against carbapenemase-producing Enterobacter sp. This simultaneous activity of compounds against different growth forms of both gram-positive and gram-negative bacteria is rare. Genome sequencing of spontaneous resistant mutants and proteome analysis suggest that resistance is mediated by downregulation of the bacterial EIIBC phosphotransferase components scrA and mtlA in MRSA likely leading to a lower uptake of the molecules. Due to their only moderate cytotoxicity against human cell lines, phenoxyphenols provide an interesting new scaffold for development of antimicrobial agents with activity against planktonic cells, persisters and biofilm-incoporated cells of ESKAPE pathogens. KEY POINTS: • Brominated phenoxyphenols kill actively replicating and biofilm-incorporated bacteria. • Phosphotransferase systems mediate uptake of brominated phenoxyphenols. • Downregulation of phosphotransferase systems mediate resistance.

Targeting virulence factors as an antimicrobial approach: Pigment inhibitors

The fascinating and dangerous colored pathogens contain unique chemically pigmented molecules, which give varied and efficient assistance as virulence factors to the crucial reproduction and growth of microbes. Therefore, multiple novel strategies and inhibitors have been developed in recent years that target virulence factor pigments. However, despite the importance and significance of this topic, it has not yet been comprehensively reviewed. Moreover, research groups around the world have made successful progress against antibacterial infections by targeting pigment production, including our serial works on the discovery of CrtN inhibitors against staphyloxanthin production in Staphylococcus aureus. On the basis of the previous achievements and recent progress of our group in this field, this article will be the first comprehensive review of pigment inhibitors against colored pathogens, especially S. aureus infections, and this article includes design strategies, representative case studies, advantages, limitations, and perspectives to guide future research.

Anthranilic Acid Inhibitors of Undecaprenyl Pyrophosphate Synthase (UppS), an Essential Enzyme for Bacterial Cell Wall Biosynthesis

We report the successful implementation of virtual screening in the discovery of new inhibitors of undecaprenyl pyrophosphate synthase (UppS) from Escherichia coli. UppS is an essential enzyme in the biosynthesis of bacterial cell wall. It catalyzes the condensation of farnesyl pyrophosphate (FPP) with eight consecutive isopentenyl pyrophosphate units (IPP), in which new cis-double bonds are formed, to generate undecaprenyl pyrophosphate. The latter serves as a lipid carrier for peptidoglycan synthesis, thus representing an important target in the antibacterial drug design. A pharmacophore model was designed on a known bisphosphonate BPH-629 and used to prepare an enriched compound library that was further docked into UppS conformational ensemble generated by molecular dynamics experiment. The docking resulted in three anthranilic acid derivatives with promising inhibitory activity against UppS. Compound 2 displayed high inhibitory potency (IC₅₀ = 25 μM) and good antibacterial activity against E. coli BW25113 ΔtolC strain (MIC = 0.5 μg/mL).

Bacteriophages: Protagonists of a Post-Antibiotic Era

Despite their long success for more than half a century, antibiotics are currently under the spotlight due to the emergence of multidrug-resistant bacteria. The development of new alternative treatments is of particular interest in the fight against bacterial resistance. Bacteriophages (phages) are natural killers of bacteria and are an excellent tool due to their specificity and ecological safety. Here, we highlight some of their advantages and drawbacks as potential therapeutic agents. Interestingly, phages are not only attractive from a clinical point of view, but other areas, such as agriculture, food control, or industry, are also areas for their potential application. Therefore, we propose phages as a real alternative to current antibiotics.

Synergistic bacterial inactivation by combining antibiotics with nanosecond electric pulses

Antibiotic resistance mechanisms render current antibiotics ineffective, requiring higher concentrations of existing drugs or the development of more powerful drugs for infection treatment. This study demonstrates the synergistic inactivation of a gram-positive (Staphylococcus aureus) and a gram-negative (Escherichia coli) bacteria by combining either tobramycin or rifampicin with 300-ns electric pulses (EPs). For EPs depositing the same total energy density into the sample with no drug, higher electric fields induced greater inactivation, indicating a threshold for irreversible electroporation at these fields and membrane recovery in between lower intensity EPs. Synergistic inactivation generally increased with increasing drug concentration up to 20 μg/mL compared to strictly EP treatment. Combining even 1/20 of the clinical dose of tobramycin with a train of EPs induced between 2.5 and 3.5 log inactivation after only 10 min of exposure compared to hours to induce inactivation with a clinical dose with no EPs. Similarly, combining a train of EPs with a clinically relevant dose of rifampicin induced 7 to 9 log inactivation over the same time of exposure. These results indicate the promise of combining EPs with antibiotics to rapidly inactivate antibiotic-resistant bacteria in localized treatment areas.