The usnic acid derivative peziculone targets cell walls of Gram-positive bacteria revealed by high-throughput CRISPRi-seq analysis

Natural Product Usnic Acid as an Antibacterial Therapeutic Agent: Current Achievements and Further Prospects

Antimicrobial resistance (AMR) poses a significant global public health threat, endangering both human and animal health. In clinical environments, AMR often undermines the effectiveness of antibacterial treatments, underscoring the urgent need to discover and develop new antibacterial agents or alternatives to antibiotics. Usnic acid, a secondary metabolite derived from lichens, has emerged as a promising candidate owing to its diverse pharmacological properties, which include antibacterial, immune-regulating, antiaging, and anti-inflammatory activities. Extensive research has shown that usnic acid exhibits strong direct antibacterial effects against Gram-positive bacteria and acts as an antimicrobial adjuvant to enhance the therapeutic efficacy of antibiotic drugs against Gram-negative pathogens. Its mechanisms of action are multifaceted, encompassing the inhibition of RNA, DNA, and protein synthesis; suppression of bacterial efflux pump protein expression and membrane-localized drug-resistant enzyme activity; disruption of cell membrane integrity and metabolic homeostasis; and reduction of virulence factor production and biofilm formation. Despite its potential, the clinical application of usnic acid as an antibacterial agent faces significant challenges including poor aqueous solubility, low bioavailability, and dose-dependent toxicity. To overcome these limitations, nanodelivery systems such as liposomes and polymeric nanoparticles have been developed to enhance solubility, improve targeted delivery, and reduce toxicity, thereby expanding its therapeutic potential. Structural modification can also enhance the antibacterial activity and address solubility issues. This review systematically consolidates current knowledge on usnic acid's antibacterial properties, molecular mechanisms, and combinatorial therapies. It critically evaluates advancements in nanoformulation strategies, assesses safety and toxicity profiles, and identifies obstacles to its development as a clinically viable antibacterial agent. By addressing these aspects, this review aims to provide actionable insights, foster interdisciplinary dialogue, and catalyze further innovation in leveraging this natural product to combat AMR.

Usnic acid and tannic acid as inhibitors of coccidia and Clostridium perfringens: alleviating necrotic enteritis and improving intestinal health in broiler chickens

BACKGROUND

Necrotic enteritis (NE) in broiler chickens leads to significant economic losses in poultry production. This study examined the inhibitory effects of usnic acid and tannic acid on coccidia, sporozoite, and Clostridium perfringens and assessed their influence on growth performance and intestinal health in NE-challenged broilers through in vitro and in vivo experiments.

METHODS

The in vitro experiment included 5 treatment groups: the negative control (NC), 2 μmol/L diclazuril (DZ), 30 μmol/L usnic acid (UA), 90 μmol/L tannic acid (TA), and 15 μmol/L usnic acid + 45 μmol/L tannic acid (UTA) groups. The in vivo experiment involved 320 broilers divided into four groups: PC (NE-challenged), SA (500 mg/kg salinomycin premix + NE-challenged), UA (300 mg/kg usnic acid + NE-challenged), and UTA (300 mg/kg usnic acid + 500 mg/kg tannic acid + NE-challenged) groups.

RESULTS

In the in vitro study, the UA, TA, and UTA treatments significantly increased apoptosis in coccidian oocysts and sporozoites, lowered the mitochondrial membrane potential (P < 0.05), and disrupted the oocyst structure compared with those in the NC group. UA and TA had inhibitory effects on C. perfringens, with the strongest inhibition observed in the UTA group. The in vivo results demonstrated that the SA group presented significantly improved growth performance on d 13, 21, and 28 (P < 0.05), whereas the UA and UTA groups presented improvements on d 13 and 21 (P < 0.05). The SA, UA, and UTA treatments reduced the intestinal lesion scores by d 28 and the fecal coccidian oocyst counts from d 19 to 21 (P < 0.05). Compared with the PC group, the UA and UTA groups presented lower intestinal sIgA levels and CD8+ cell percentages (P < 0.05), with a trend toward a reduced CD3+ cell percentage (P = 0.069). The SA, UA, and UTA treatments significantly reduced the serum diamine oxidase activity, crypt depth, and platelet-derived growth factor levels in the intestinal mucosa while increasing the villus height to crypt depth ratio and number of goblet cells (P < 0.05). The UTA treatment also significantly increased the acetate and butyrate concentrations in the cecum (P < 0.05). With respect to the gut microbiota, significant changes in β diversity in the ileum and cecum were observed in the SA, UA, and UTA groups, indicating that the microbial community compositions differed among the groups. Romboutsia dominated the SA group, Bacillales dominated the UA group, and Lactobacillales and Lachnospirales dominated the UTA group in the ileal microbiota. In the cecal microbiota, Lactobacillus, Butyricicoccus, and Blautia abundances were significantly elevated in the UTA group (P < 0.05).

CONCLUSION

Usnic acid and tannic acid induce apoptosis in coccidia and sporozoites by lowering the mitochondrial membrane potential. Both usnic acid alone and in combination with tannic acid alleviate NE-induced adverse effects in broilers by modulating intestinal immunity, altering the microbial composition, and improving intestinal barrier function. Compared with usnic acid alone, the combination of usnic acid and tannic acid had superior effects, providing a promising basis for the development of effective feed additive combinations.

Metabolic engineering approaches for the biosynthesis of antibiotics

BACKGROUND

Antibiotics have been saving countless lives from deadly infectious diseases, which we now often take for granted. However, we are currently witnessing a significant rise in the emergence of multidrug-resistant (MDR) bacteria, making these infections increasingly difficult to treat in hospitals.

MAIN TEXT

The discovery and development of new antibiotic has slowed, largely due to reduced profitability, as antibiotics often lose effectiveness quickly as pathogenic bacteria evolve into MDR strains. To address this challenge, metabolic engineering has recently become crucial in developing efficient enzymes and cell factories capable of producing both existing antibiotics and a wide range of new derivatives and analogs. In this paper, we review recent tools and strategies in metabolic engineering and synthetic biology for antibiotic discovery and the efficient production of antibiotics, their derivatives, and analogs, along with representative examples.

CONCLUSION

These metabolic engineering and synthetic biology strategies offer promising potential to revitalize the discovery and development of new antibiotics, providing renewed hope in humanity's fight against MDR pathogenic bacteria.

The rise and future of CRISPR-based approaches for high-throughput genomics

Clustered regularly interspaced short palindromic repeats (CRISPR) has revolutionized the field of genome editing. To circumvent the permanent modifications made by traditional CRISPR techniques and facilitate the study of both essential and nonessential genes, CRISPR interference (CRISPRi) was developed. This gene-silencing technique employs a deactivated Cas effector protein and a guide RNA to block transcription initiation or elongation. Continuous improvements and a better understanding of the mechanism of CRISPRi have expanded its scope, facilitating genome-wide high-throughput screens to investigate the genetic basis of phenotypes. Additionally, emerging CRISPR-based alternatives have further expanded the possibilities for genetic screening. This review delves into the mechanism of CRISPRi, compares it with other high-throughput gene-perturbation techniques, and highlights its superior capacities for studying complex microbial traits. We also explore the evolution of CRISPRi, emphasizing enhancements that have increased its capabilities, including multiplexing, inducibility, titratability, predictable knockdown efficacy, and adaptability to nonmodel microorganisms. Beyond CRISPRi, we discuss CRISPR activation, RNA-targeting CRISPR systems, and single-nucleotide resolution perturbation techniques for their potential in genome-wide high-throughput screens in microorganisms. Collectively, this review gives a comprehensive overview of the general workflow of a genome-wide CRISPRi screen, with an extensive discussion of strengths and weaknesses, future directions, and potential alternatives.

New Fe3O4-Based Coatings with Enhanced Anti-Biofilm Activity for Medical Devices

With the increasing use of invasive, interventional, indwelling, and implanted medical devices, healthcare-associated infections caused by pathogenic biofilms have become a major cause of morbidity and mortality. Herein, we present the fabrication, characterization, and in vitro evaluation of biocompatibility and anti-biofilm properties of new coatings based on Fe3O4 nanoparticles (NPs) loaded with usnic acid (UA) and ceftriaxone (CEF). Sodium lauryl sulfate (SLS) was employed as a stabilizer and modulator of the polarity, dispersibility, shape, and anti-biofilm properties of the magnetite nanoparticles. The resulting Fe3O4 functionalized NPs, namely Fe3O4@SLS, Fe3O4@SLS/UA, and Fe3O4@SLS/CEF, respectively, were prepared by co-precipitation method and fully characterized by XRD, TEM, SAED, SEM, FTIR, and TGA. They were further used to produce nanostructured coatings by matrix-assisted pulsed laser evaporation (MAPLE) technique. The biocompatibility of the coatings was assessed by measuring the cell viability, lactate dehydrogenase release, and nitric oxide level in the culture medium and by evaluating the actin cytoskeleton morphology of murine pre-osteoblasts. All prepared nanostructured coatings exhibited good biocompatibility. Biofilm growth inhibition ability was tested at 24 h and 48 h against Staphylococcus aureus and Pseudomonas aeruginosa as representative models for Gram-positive and Gram-negative bacteria. The coatings demonstrated good biocompatibility, promoting osteoblast adhesion, migration, and growth without significant impact on cell viability or morphology, highlighting their potential for developing safe and effective antibacterial surfaces.

Azalomycin F4a targets peptidoglycan synthesis of Gram-positive bacteria revealed by high-throughput CRISPRi-seq analysis

Azalomycin F4a is a promising 36-membered polyhydroxy macrolide that shows antibacterial activity against drug-resistant Gram-positive bacteria, but its exact working mechanism remains to be elusive. Here, we isolated the azalomycin F4a product from a Streptomyces solisilvae and demonstrated its antibacterial activity against Gram-positive pathogens including Streptococcus pneumoniae, Staphylococcus aureus and methicillin-resistant Staphylococcus aureus (MRSA). We further showed that combination of azalomycin F4a with methicillin has an additive antimicrobial effect on MRSA, where the minimal inhibitory concentrations (MIC) of methicillin to MRSA was decreased by 1000-fold in the presence of sublethal concentration of azalomycin F4a. A CRISPRi-seq based whole genome screen was employed to identify the potential targets of azalomycin F4a, which revealed that peptidoglycan synthesis (PGS) was inhibited by azalomycin F4a. Furthermore, azalomycin F4a treatment could significantly impair S. aureus biofilm formation. Our research highlights that cell wall synthesis is an additional target for novel classes of macrolide besides ribosome.