Staphylococcus aureus poses a global threat to livestock health and public health security, necessitating a novel antibiotic. Pleuromutilin, a natural antibiotic, has served as a promising foundation for developing new antibacterial agents through structural modification. This study aims to evaluate the antibacterial potential, safety, and pharmacokinetic profile of a novel pleuromutilin derivative 2-3 (22-[2-(L-prolylamino)phenylsulfanyl]-22-deoxypleuromutilin). The compound 2-3 exhibited potent antibacterial activity (MIC = 0.25 μg/mL), concentration-dependent bactericidal effects, and prolonged post-antibiotic effects (PAEs). Safety assessments revealed low cytotoxicity (CC50 = 62.63 μg/mL) and no observable hemolytic activity. In vitro metabolic studies indicated species-dependent clearance, primarily mediated by CYP3A4. Pharmacokinetic in rats showed rapid absorption and elimination, with oral and intramuscular bioavailability of 16.03% ± 8.82% and 53.36% ± 12.27%, respectively. Notably, 2-3 demonstrated superior efficacy over tiamulin in a neutropenic murine thigh infection model. Molecular docking revealed a stronger binding free energy between 2-3 and the 50S ribosomal subunit compared to tiamulin. Collectively, these results highlight 2-3 as a promising clinical candidate against S. aureus infections, characterized by enhanced efficacy and a favorable safety profile.

Colorectal cancer, which originates in the epithelial cells of the colon or rectum, is closely associated with dysbiosis of the gut microbiota. Increasing evidence has shown that Fusobacterium nucleatum plays a significant role in colorectal cancer progression by activating inflammatory responses, modulating the tumor microenvironment, and promoting tumor cell proliferation. Antimicrobial peptides targeting Fusobacterium nucleatum have the potential to serve as more effective and less toxic therapeutic agents compared to chemotherapy drugs. In this study, we systematically evaluated the antibacterial activity of Trp-containing peptides, including natural peptides isolated from the skin secretions of the Chinese brown frog (Rana chensinensis) and their derivatives, which exhibit potent antibacterial activity against Fusobacterium nucleatum with minimal cytotoxicity. Mechanistic investigations using membrane permeability assays and membrane potential-sensitive dyes indicated that Trp-containing peptides exert their antimicrobial effects by disrupting the bacterial membrane structure, increasing membrane permeability, and interfering with membrane potential. In a colorectal cancer mouse model infected with Fusobacterium nucleatum, treatment with Trp-containing peptides significantly alleviated tumor-related symptoms, reduced colonic inflammatory cytokine levels, and alleviated colonic tissue damage, as confirmed by histopathological analysis. Importantly, no apparent toxicity or adverse effects were observed during the treatment. These findings indicate that Trp-containing peptides, as lead compounds, not only exhibit potent antibacterial activity but also attenuate Fusobacterium nucleatum associated colorectal cancer progression, providing critical evidence to support the development of innovative therapeutic strategies with combined antimicrobial and antitumor properties.

Plasmepsin V (PMV), an essential aspartyl protease, plays a critical role during the asexual blood stage of infection of Plasmodium by enabling the export of parasite proteins into the host red blood cell. This export is vital for parasite survival and pathogenesis, making PMV an attractive target for antimalarial drug development. Peptidomimetic inhibitors designed to mimic the natural substrate of PMV have demonstrated potent parasite-killing activity by blocking protein export. While these compounds have been instrumental in validating PMV as a bona fide antimalarial target, inconsistencies between their biochemical potency and cellular activity have raised questions regarding their precise mechanism of action. In this study, we employed chemoproteomic approaches, including solvent-induced protein precipitation and intact-cell thermal profiling, to demonstrate PMV target engagement by the peptidomimetics. To further support these findings, we generated parasite lines exhibiting reduced sensitivity to peptidomimetics. Through whole-genome sequencing of these parasite lines, a single nucleotide variant within the pmv gene was revealed. This mutation was later validated using reverse genetics, confirming its role in mediating resistance. Together, these data provide strong evidence that the peptidomimetics exert their antimalarial activity by directly targeting PMV. These findings further support the potential of PMV as a validated and promising target for future antimalarial drug development.

The F1FO-ATP synthase is essential to the aerobe Acinetobacter baumannii. Its FO-domain utilizes the proton motive force to rotate the turbine (c10-ring) inside the stator (a subunit), which generates a torque that is translated to the catalytic F1-domain for adenosine 5'-triphosphate (ATP) synthesis. Here, we investigated key features of the FO-domain, including the proton intake channel, proton donor and acceptor residues, an A. baumannii unique subunit a helix, and the proton exit pathway. By employing a heterologous system, we generated mutants and studied their growth kinetic properties in minimal media, as well as the ATP synthesis activity of their inverted-membrane vesicles. The findings highlight the front entry as the main proton uptake pathway and the key residues involved in proton translocation. Molecular dynamics (MD) simulations confirm the role of these charged residues, which interact with water molecules to facilitate a water-mediated proton transfer in a Grotthuss-like mechanism. Similarly, the exit channel with R224 of subunit a playing a central role is described. Importantly, the sequential flow of proton intake, turbine rotation, and proton release are modulated by the unique a subunit helix, which functions like a molecular ratchet to facilitate effective proton transfer for the final formation of ATP. The importance in function, difference in amino acid content, and uniqueness in regulation by its specific molecular ratchet make the A. baumannii proton pathway an attractive inhibitor target, where a cork-like molecule could prevent proton intake and/or release with the consequence of ATP synthesis and cell growth inhibition.

Polymyxins are considered last-resort antibiotics for multidrug-resistant Gram-negative bacteria. However, their clinical utility is limited by toxicities, particularly nephrotoxicity and neurotoxicity, as well as the emergence of resistance. This review addresses these challenges and evaluates strategic interventions aimed at enhancing the efficacy of polymyxins while mitigating their adverse effects. Combination therapies have emerged as a cornerstone strategy. These therapies can be categorized into five frameworks: structural barrier disruption, bioenergetic flux modulation, metabolic homeostasis disruption, resistance neutralization, and virulence disarming. In addition to synergistic agents, complementary strategies such as detoxifying adjuvants and advanced delivery systems have been systematically integrated to overcome the intrinsic limitations of polymyxins. Collectively, these multifaceted strategies enhance the antibacterial activity of polymyxins against Gram-negative bacteria, while simultaneously reducing effective doses, minimizing toxicity, and mitigating the development of resistance. These innovations represent a pivotal advance in revitalizing polymyxin therapy in the era of multidrug resistance.

Bacterial strains are distinguished by surface glycans composed of defined sugar sequences that include "rare" monosaccharides, which are absent in human glycans and help to mediate host-microbe interactions. One of the most prevalent rare sugars is l-Rhamnose (l-Rha), and human sera are generally enriched in anti-l-Rha antibodies; however, the source of l-Rha antigens is unknown. Here, we synthesize a surface glycan l-Rha-N-acetyl glucosamine disaccharide sequence, which is found across many bacterial species, to evaluate binding motifs of human anti-glycan antibodies in clinical and commercial human sera. We find that sera are enriched in IgG antibodies that react with this disaccharide probe. Through capture of bound antibodies and analysis with surface glycan sequences from different strains, we observe that bound human antibodies appear to recognize free or branched, but not internal, l-Rha motifs. Overall, this work details the isolation of naturally occurring anti-l-Rha human antibodies and promotes an understanding of their carbohydrate recognition epitopes.

Bacterial glycans are complex and often presented on the surface of the cell as a level of protection. These glycans offer an opportunity to screen for new antibiotic targets and immunological markers. Here recent developments in the field of glycan arrays are presented as opportunities to advance therapies for human health.

Mycobacterium tuberculosis (Mtb), the causative agent of human tuberculosis (TB), employs its de novo histidine (His) biosynthesis to escape host-inflicted His starvation. This makes the enzymes involved in this biosynthetic pathway promising anti-TB drug targets. In this study, employing the high-resolution crystal structure of imidazole glycerol phosphate dehydratase (IGPD) of the Mtb His pathway, three triazole scaffold molecules were identified as potential inhibitors of this enzyme. These high-resolution crystal structures of the enzyme-inhibitor complexes elucidated the key interactions responsible for their binding specificity and affinity. We also studied the interactions of these inhibitors with the enzyme at the atomic level and tested their cytotoxicity and efficacy in in vitro and in vivo models. Our findings revealed that the most prominent inhibitor, SF2, was safe in mice and effectively inhibited the in vitro growth of both free as well as in macrophage-internalized wild-type and drug-resistant Mtb clinical isolates. Notably, SF2 also showed a marginal reduction in the bacterial load in organs of mice infected with Mtb. Collectively, these findings advocate the chemical inhibition of IGPD of the His pathway as a novel anti-Mtb therapeutic strategy.

Methicillin-resistant Staphylococcus aureus (MRSA) ST398 carries two hyaluronidase genes, hysA and its homologue hysAνSaβ, the latter located on the genomic island νSaβ. However, the prevalence of hysAνSaβ and its contribution to virulence remain unclear. Here, we report that the hysAνSaβ gene is present in 18.3% (4707/25,752) of S. aureus in the NCBI database, with ST398 being the most prevalent sequence type (30.9%, 1457/4707). In ST398, the hysAνSaβ gene is flanked by IS21 and IS3, with >99.0% nucleotide identity across strains, suggesting horizontal acquisition. In a mouse skin infection model, a wild-type ST398 MRSA strain carrying both hysA and hysAνSaβ formed significantly larger abscesses than isogenic mutants lacking one or both hyaluronidase genes. Wild-type infection led to a higher bacterial load and sustained induction of chemokines (CCL5, CXCL1, CCL4) and pro-inflammatory cytokines (IL-1β, IL-6, IL-33), resulting in prolonged neutrophil recruitment and severe inflammation. Consistently, hysA and hysAνSaβ enhanced the survival of MRSA ST398 inside RAW 264.7 macrophages and neutrophils. In vitro, a double knockout strain (ΔhysA-ΔhysAνSaβ) grew more slowly with hyaluronic acid (HA) as the sole carbon source, accompanied by intracellular accumulation of specific amino acids (proline, valine, threonine, and phenylalanine) and downregulation of amino acid biosynthesis pathways. Moreover, RAW 264.7 macrophages infected with ΔhysA-ΔhysAνSaβ showed a marked upregulation of the oxidative phosphorylation (OXPHOS) pathway compared to uninfected controls, suggesting an enhanced cellular metabolic and inflammatory response that could improve bacterial clearance. Our findings highlight the functionally redundant roles of hysA and hysAνSaβ in MRSA ST398 pathogenesis, suggesting that these hyaluronidases are potential targets for antistaphylococcal therapy.