Biology subjects

Gunasekera, R. S.

Publications and source records attributed to Gunasekera, R. S..

4 recordsLinked to original sources

bioRxiv2026

Characterizations of Antibacterial and Anti-biofilm Properties of Dendrimers G6 and G9

Dendrimers are nanosized molecules with potential antimicrobial applications. This study evaluates the antibacterial and anti-biofilm properties of two cationic dendrimers, NVX-G6 (G6) and NVX-G9 (G9), against clinically relevant bacterial pathogens. Minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC99) were determined for Escherichia coli, Pseudomonas aeruginosa, methicillin-sensitive Staphylococcus aureus (MSSA), and methicillin-resistant Staphylococcus aureus (MRSA). The synergy of dendrimers with ceftazidime and vancomycin was evaluated using checkerboard assays. Furthermore, biofilm formation inhibition assays and fluorescent microscopy were performed to assess dendrimer interactions with bacterial biofilms. The results indicate that G6 and G9 exhibit limited direct antibacterial activity at high concentrations (MIC > 1024 {micro}g/mL) but demonstrate synergistic effects when combined with ceftazidime against E. coli and P. aeruginosa (FIC < 0.5). Notably, both dendrimers penetrated and colocalized within established biofilms, with time-dependent reductions in biomass observed after extended incubation, suggesting a role in progressive biofilm disruption rather than acute inhibition of formation, although significant biomass reduction was not observed under standard assay conditions. These findings contribute to the understanding of dendrimer-antibiotic interactions and their implications in antimicrobial and nanomedicine therapy.

microbiology↗

bioRxiv2024

Green Synthesized Magnolia alba Silver Nanoparticles Kill Pathogens, Inhibit Cancer, and Display Antioxidant and Photocatalytic Properties

The biosynthesis of silver nanoparticles has recently emerged as a promising approach in nanomedicine, particularly for targeted therapeutic applications. Green synthesized (plant-based) nanoparticles have been shown to offer enhanced reduction efficiency, greater bioavailability, and improved stability compared to synthetic nanoparticles. Here, we report the green synthesis of silver nanoparticles (AgNPs) using Magnolia alba leaf extract. The formation of these Magnolia-derived silver nanoparticles (MAgNPs) was verified through UV-Vis spectroscopy and further characterized by scanning electron microscopy (SEM) which showed that the MAgNPs have a mean diameter of 40 nm and a spherical morphology. The antibacterial efficacy of MAgNPs, evaluated by the well diffusion method, showed significant activity against E. coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Enterococcus faecalis, and strains of methicillin-resistant and -sensitive Staphylococcus aureus. Disc diffusion and plaque assays demonstrated notable antifungal activity against Candida albicans and antiviral activity against bacteriophage T7. In vitro studies with HCT-116 human colon cancer cells, MAgNPs exhibited significant bi-phasic inhibition of cancer cell growth. These effects were greater than that of the magnolia leaf extracts alone, confirming the green synthesized nanoparticles bioactive efficacy. These findings suggest that MAgNPs possess significant antimicrobial and anticancer activities, indicating their potential as therapeutic agents for certain infections and cancers. Antioxidant assays indicated that MAgNPs exhibit greater antioxidant activity than magnolia leaf extract alone. Results suggest that MAgNPs may have promise as antioxidants for treating free radical-induced disorders. Additionally, MAgNPs showed efficient photocatalytic degradation of the azo bond in methyl orange within 30 minutes, suggesting they may provide a sustainable approach to certain types of environmental pollution. To our knowledge, this is the first report of the biosynthesis of silver nanoparticles using Magnolia alba and examination of their antioxidant and photocatalytic properties, their killing and inhibitory effects on various bacteria, fungi, bacteriophages, and colon cancer.

bioengineering↗

bioRxiv2024

Microbicidal Mechanisms for Light-Activated Molecular Nanomachines in Mycobacterium smegmatis: A Model for Pathogenic Bacteria

There is a global health crisis of antimicrobial resistance, with over a million deaths annually attributed to antimicrobial-resistant pathogens, and mycobacterial infections are a major cause of antimicrobial-resistant infections, leading to more deaths than any other single infectious agent. Notably, the rise of multidrug-resistant (MDR), extensively drug-resistant (XDR), and totally drug-resistant (TDR) strains of Mycobacterium tuberculosis led to higher mortality rates and challenge all existing antibiotic regimens. Light-activated molecular nanomachines (MNMs) represent a promising class of broad-spectrum antimicrobial agents that could help counter this rise in antimicrobial resistance. Addressing a key knowledge gap, this study explores the mechanisms of action for MNMs in Mycobacterium smegmatis, a surrogate model for pathogenic mycobacteria. We show that fast rotor MNMs kill up to 97% of M. smegmatis and co-localize with the bacteria as part of their mechanism of action. The ability to translate these observations to pathogenic mycobacteria was demonstrated by the ability of MNMs to kill 93.5% of M. tuberculosis under similar conditions. These findings suggest that MNMs may provide innovative sustainable antimicrobial agents for the treatment of drug-resistant mycobacterial infections. Graphical AbstractBacteria exposed to MNMs have two distinct outcomes when activated by 365 nm light. Slow motors (MNM 2 and 4) have no rotational action, remains outside the bacteria and have little to no effect on bacterial viability. Whereas fast motors (MNM 1 and 3) co-localize and embed into the bacterial cell wall causing disruptions that lead to a significant reduction in bacterial viability. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=89 SRC="FIGDIR/small/616754v1_ufig1.gif" ALT="Figure 1"> View larger version (30K): org.highwire.dtl.DTLVardef@70991corg.highwire.dtl.DTLVardef@541a36org.highwire.dtl.DTLVardef@18504bcorg.highwire.dtl.DTLVardef@1fa08c3_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗

bioRxiv2022

ORFanID: A Web-Based Search Engine for the Discovery and Identification of Orphan and Taxonomically Restricted Genes

With the numerous genomes sequenced today, it has been revealed that a noteworthy percentage of genes in a given taxon of organisms in the phylogenetic tree of life do not have orthologous sequences in other taxa. These sequences are commonly referred to as "orphans" or "ORFans" if found as single occurrences in a single species or as "taxonomically restricted genes" (TRGs) when found at higher taxonomic levels. Quantitative and collective studies of these genes are necessary for understanding their biological origins. However, the current software for identifying orphan genes is limited in its functionality, database search range, and very complex algorithmically. Thus, researchers studying orphan genes must harvest their data from many disparate sources. ORFanID is a graphical web-based search engine that facilitates the efficient identification of both orphan genes and TRGs at all taxonomic levels, from DNA or amino acid sequences in the NCBI database cluster and other large bioinformatics repositories. The software allows users to identify genes that are unique to any taxonomic rank, from species to domain, using NCBI systematic classifiers. It provides control over NCBI database search parameters, and the results are presented in a spreadsheet as well as a graphical display. The tables in the software are sortable, and results can be filtered using the fuzzy search functionality. The visual presentation can be expanded and collapsed by the taxonomic tree to its various branches. Example results from searches on five species and gene expression data from specific orphan genes are provided in the Supplementary Information. Availability and ImplementationThe ORFanID web application and database can be accessed at http://www.orfangenes.com/. The website provides textual and video instructions on how to use the tool. The Source Code for ORFanID is available at https://github.com/orfanid.

bioinformatics↗