Abstract
Biofilms not only protect bacteria and Candida species from antibiotics, but they also promote the emergence of drug-resistant strains, making eradication more challenging. As a result, novel antimicrobial agents to counteract biofilm formation are desperately needed. In this study, Terminalia catappa leaf extract (TCE) was used to optimize the TCE-capped silver nanoparticles (TCE-AgNPs) via a one-pot single-step method. Varied concentrations of TCE have yielded different sized AgNPs. The physico-chemical characterization of TCE-AgNPs using UV-Vis, SEM, TEM, FTIR, and Raman spectroscopy have confirmed the formation of nanostructures, their shape and size and plausible role of TCE bio-active compounds, most likely involved in the synthesis as well as stabilization of NPs, respectively. TCE-AgNPs have been tested for antibiofilm and antimicrobial activity against multidrug-resistant Pseudomonas aeruginosa (MDR-PA), methicillin-resistant Staphylococcus aureus (MRSA), and Candida albicans using various microbiological protocols. TCE-Ag-NPs−3 significantly inhibits biofilm formation of MDR-PA, MRSA, and C. albicans by 73.7, 69.56, and 63.63%, respectively, at a concentration of 7.8 µg/mL, as determined by crystal violet microtiter assay. Furthermore, SEM micrograph shows that TCE-AgNPs significantly inhibit the colonization and adherence of biofilm forming cells; individual cells with loss of cell wall and membrane integrity were also observed, suggesting that the biofilm architecture and EPS matrix were severely damaged. Moreover, TEM and SEM images showed that TCE-AgNPs brutally damaged the cell wall and membranes of MDR-PA, MRSA, and C. albicans. Additionally, extreme ultrastructural changes such as deformation, disintegration, and separation of cell wall and membrane from the cells, have also been observed, indicating significant loss of membrane and cell wall integrity, which eventually led to cell death. Overall, the research revealed a simple, environmentally friendly, and low-cost method for producing colloidal TCE-AgNPs with promising applications in advanced clinical settings against broad-spectrum biofilm-forming antibiotic-resistant bacteria and candida strains.
Highlights
The Gram-negative multidrug-resistant Pseudomonas aeruginosa (MDR-PA) and Grampositive methicillin-resistant Staphylococcus aureus (MRSA) human pathogens are the leading causes of nosocomial infections in hospitals globally [1,2]
The role of bio-actives molecules contributed by animal, microbial, and plant cells and tissues in bio-inspired nanomaterial synthesis has been recognized, with the ultimate potential to reduce a wide range of metal cations to nano size particles [34,35,36]
Benign extracts of explants such as leaves, root, stem, bark, and seed typically act as bio-factory for the synthesis of a wide range of bio-actives including long and short hydrocarbon chains, aromatic complex cyclic compounds, polyphenols, alkaloids, flavonoids, terpenoids, sugars, proteins, and enzymes naturally [8,10,30,31]
Summary
The Gram-negative multidrug-resistant Pseudomonas aeruginosa (MDR-PA) and Grampositive methicillin-resistant Staphylococcus aureus (MRSA) human pathogens are the leading causes of nosocomial infections in hospitals globally [1,2]. Matured biofilms of MDR-PA, MRSA, and C. albicans are comprised of a complex three-dimensional structure of multiple stacked layers and aggregated clusters of their cells, hyphae, extracellular DNA, proteins, and abundant exopolysaccharide (EPS) matrix [5,6,7]. Establishment and maturation of biofilms of such microbial pathogens on a number of medical devices such as dental restorative fillings, orthopedic implants, contact lenses, and catheters have been accounted majorly for the failure of biomaterial-based medical implants and traditional antibiotics. A variety of medicinal crude extracts and essential oils containing bio-active carbohydrates, terpenoids, polyphenols, alkaloids, phenolic acids, and proteins have been used as well as these bioactives-capped metal nanoparticles have been employed such as potential antimicrobial, antibiofilm, and antiquorum sensing agents [8,9]
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