Biology subjects

Maset, R. G.

Publications and source records attributed to Maset, R. G..

5 recordsLinked to original sources

bioRxiv2026

Uncovering the multifaceted mechanism of action of a historical antimicrobial

Natural products have provided most of our modern pharmacopoeia, serving as active molecules or scaffolds for active molecules. Their use in drug development is often inspired by their traditional or historical medical use. For many decades, this discovery pipeline has focused on identifying a single molecule responsible for much of the biological activity of a raw natural product preparation (e.g. a whole-plant extract) and scoping this molecule for clinical potential. However, it is increasingly realised that historical/traditional remedies with significant biological activity may owe this activity to the combined action of multiple molecules. Concomitantly, microbiologists increasingly argue that effectively fighting antimicrobial-resistant infections will rely on combination therapies that combine multiple antimicrobials and/or adjuvant molecules. We previously reconstructed a complex historical remedy, Bald's eyesalve. Our reconstruction of this remedy had strong antibiofilm activity, which relied on the presence of multiple ingredients. Here, we report that Bald's eyesalve has multiple antibacterial effects on exemplar Gram-positive (Staphylococcus aureus) and Gram-negative (Acinetobacter baumannii) pathogens. Bald's eyesalve disrupts bacterial membrane integrity; inhibits expression of genes associated with bacterial adhesins, virulence factors and efflux pumps in both S. aureus and A. baumannii; inhibits quorum sensing in S. aureus; and causes downregulation of genes involved in de novo nucleotide biosynthesis in S. aureus. Lastly, we show that this multifaceted mechanism of action makes it difficult for S. aureus, A. baumannii, and Pseudomonas aeruginosa to evolve resistance against Bald's eyesalve. Bald's eyesalve could be used to identify a defined cocktail of natural products suitable for preclinical testing as a multi-target antibacterial preparation to which resistance may arise more slowly than current single-molecule antibiotics.

microbiology↗

bioRxiv2026

Gut-relevant short-chain fatty acids modulate host-pathogen dynamics of uropathogenic Escherichia coli at the colonic epithelial interface

Urinary tract infection (UTI) ranks among the most prevalent bacterial infections worldwide, affecting over 400 million people each year. Uropathogenic Escherichia coli (UPEC), the main aetiological cause of UTI, colonises the intestinal tract, which is thought to serve as a distal reservoir for gut-UTI recurrence. Despite this, the precise role of the gut in UTI recurrence is still not fully defined. Recent research investigating the gut-UTI axis has revealed that reduced abundance of gut commensals producing short-chain fatty acids (SCFAs, namely acetate, butyrate and propionate) is associated with recurrent and chronic UTI. We therefore aimed to investigate the impact of these gut commensal-derived metabolites on a diverse panel of UPEC strains, including well-studied prototypical strains (UTI89, CFT073), a non-pathogenic isolate E. coli K-12, and various clinical UTI isolates (from the urine of both symptomatic and asymptomatic individuals). We observed that SCFAs modulate bacterial growth kinetics in a concentration- and pH-dependent manner, by prolonging the lag phase without affecting final carrying capacity in vitro. These metabolites further suppressed bacterial swimming motility and biased the orientation of fimS, the phase variable switch for T1 fimbriae, under acidic conditions. In a human polarized, mucus-secreting intestinal infection model, SCFA treatment during UPEC challenge altered bacterial localization patterns, favouring planktonic over mucosal-associated populations, and preserved epithelial barrier function. Together, these in vitro findings demonstrate that SCFAs modulate key UPEC colonization-associated phenotypes and influence host-pathogen dynamics at the colonic epithelial interface. These results provide mechanistic insights into how depletion of SCFA-producing gut commensals may alter the intestinal reservoir environment in vitro and warrants further investigation into the role of gut-derived SCFAs in rUTI susceptibility.

microbiology↗

bioRxiv2025

Effect of human urinary microenvironment and fluid flow on antibiotic and phage therapy efficacy against uropathogenic Escherichia coli

Urinary tract infections (UTI) remain a major global health burden, with high recurrence despite antibiotic treatment. The escalating prevalence of antimicrobial resistance further compromises therapeutic efficacy, contributing to an estimated 260,000 deaths annually. Conventional in vitro susceptibility assays often fail to predict clinical outcomes, underscoring the urgent need for physiologically relevant infection models. Here, we examined how microenvironmental complexity shapes uropathogenic Escherichia coli (UPEC) responses to antibiotics and bacteriophages using: human urine, a three-dimensional urothelial microtissue model (3D-UHU), and a novel mesofluidic system (P-FLO) that introduces physiologically relevant flow dynamics to the 3D-UHU. P-FLO was engineered from cost-effective 3D-printed components compatible with standard Transwell systems. Among the antibiotics tested, nitrofurantoin exhibited the greatest potency in minimum inhibitory concentration assays, but it failed to fully eradicate infection within the more physiological 3D-UHU model. A bacteriophage cocktail (LCPR1) showed markedly reduced activity in urine compared with nutrient-rich media, highlighting the influence of infection-site conditions. In contrast, in 3D-UHU, LCRP1 modulated host responses without reducing bacterial burden. Combination therapy (nitrofurantoin + LCPR1) eliminated planktonic bacteria under static conditions but offered no added benefit against adherent or intracellular populations relative to antibiotic monotherapy. Incorporating flow revealed additional layers of complexity, where shear stress induced bacterial elongation and attachment and altered drug performance, diminishing the efficacy of nitrofurantoin and combination therapy against planktonic populations despite increased drug exposure. Together, these findings demonstrate that the bladder microenvironment and its mechanical forces modulate host-pathogen interactions and profoundly influence UPEC infection dynamics and therapeutic outcomes, emphasizing the need for advanced, physiologically informed models to guide treatment strategies in the post-antibiotic era.

microbiology↗

bioRxiv2023

The staphylococcal type VII secretion system impacts daptomycin sensitivity through controlling bacterial cell envelope integrity

The human pathogen Staphylococcus aureus encodes a specialised type VII secretion system (T7SS), which plays an important role in bacterial virulence during infection. However, the functions the T7SS during infection and in bacterial physiology remain unclear. Here we demonstrate that S. aureus strains lacking the the T7SS effector EsxC ({Delta}esxC) was highly sensitive to the important last resort drug, daptomycin, as well as other membrane-targeting antibiotics, including gramicidin and bithionol. To understand how EsxC mediates increased antibiotic sensitivity, we investigated its functions in the staphylococcal cell envelope. Scanning electron microscopy analysis of an esxC mutant revealed a distinct cell surface morphology. Interestingly, {Delta}esxC displayed a decrease in membrane fluidity, altered membrane protein profiles and altered cell wall synthesis. The esxC mutant demonstrated enhanced daptomycin binding which correlated with the increased negative charge of mutant membranes. Calcium ions, which can bind membranes affecting charge, impacted growth of {Delta}esxC and sensitivity to daptomycin, suggesting that EsxC may modulate calcium binding to membranes. Furthermore, the esxC mutant displayed a heightened susceptibility to daptomycin during intracellular infection, and in a murine skin infection model. Thus, our data show that the T7SS effector EsxC impacts sensitivity of S. aureus to membrane-acting drugs such as daptomycin through modulation of cell membrane integrity, indicating its potential as a drug target. Author SummaryT7SS has a range of functions in bacteria including specific roles in bacterial physiology including DNA uptake, membrane integrity and bacterial development. In S. aureus T7SS has been shown to be critical for bacterial virulence, intra-species competition and in host cell interactions, although their functions in bacterial physiology are not clear. Here we report a role of the staphylococcal T7SS effector EsxC in the modulation of the cell membrane and surface integrity, which impacts the activity of membrane targeting drugs like daptomycin. Our data indicate that targeting this system could potentially enhance activity of existing therapeutic agents.

microbiology↗

bioRxiv2023

A human urothelial microtissue model reveals shared colonization and survival strategies between uropathogens and asymptomatic bacteria

Urinary tract infection is among the most common infections worldwide, and is typically studied in animals and cell lines with limited uropathogenic strains. Here, we assessed diverse bacterial pathogens and asymptomatic bacteria (ASB) in a human urothelial microtissue model including full stratification/differentiation and urine tolerance. Several uropathogens and ASB-like E. coli invaded intracellularly, suggesting invasion is a shared survival strategy, instead of a virulence hallmark. The E. coli adhesin FimH was required for intracellular community formation, but not for invasion. Other shared lifestyles included filamentation (Gram-negatives), chaining (Gram-positives) and hijacking of exfoliating cells, while biofilm-like aggregates formed mainly with Pseudomonas and Proteus. Urothelial cells expelled invasive bacteria in Rab-/LC3-decorated structures, while highly cytotoxic/invasive uropathogens, but not ASB, disrupted host barrier function and strongly induced exfoliation and cytokine production. Overall, this work highlights diverse species-/strain-specific infection strategies and corresponding host responses in a human urothelial microenvironment, providing insights at the tissue, cell and molecular level. One-Sentence SummaryA human urothelial model revealed shared colonization strategies between uropathogens and asymptomatic bacteria, and pathogen-specific innate immune responses

microbiology↗