Basanta Kumar Das, Tamasi Senapati, Jyotirmayee Pradhan, Kausalya K. Nayak, Barsha Baisakhi, Debasmita Mohanty, Mala Kumari, Swagatika Sahu

Antibacterial activity of green-synthesised silver nanoparticles (AgNPs) on major bacterial fish pathogens with emphasis on their extracellular enzymatic and haemolytic activities

Introduction

Antibacterial activity of green-synthesised silver nanoparticles (agnps) on major bacterial fish pathogens with emphasis on their extracellular enzymatic and haemolytic activities. Explore the antibacterial activity of green-synthesised silver nanoparticles (AgNPs) against major fish pathogens, inhibiting their extracellular enzymatic and haemolytic activities.

Abstract

Silver nanoparticles (AgNPs) were synthesised using a green synthesis approach using silver nitrate, starch and glucose under optimised conditions. Morphometric characterisation of the green-synthesised AgNPs was carried out by Fourier-transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), dynamic light scattering (DLS), and X-ray diffraction (XRD). The antibacterial, extracellular enzymatic and haemolytic activities of AgNPs were evaluated against nine fish pathogenic bacteria, viz., Aeromonas hydrophila (AH1), Edwardsiella tarda (ATCC15947), Pseudomonas putida (ATCC49128), Pseudomonas aeruginosa (ATCC35072), Pseudomonas fluorescens (PF1), Vibrio alginolyticus (ATCC17749), Vibrio parahaemolyticus (ATCC17802), Escherichia coli (EC1) and Staphylococcus aureus (ATCC6538). Bactericidal activity of AgNPs was assessed using both minimum inhibitory concentration (MIC) and disc diffusion assays. In A. hydrophila, starch hydrolysis was completely inhibited from 72 h onwards in cultures exposed to both 50 μl and 100 μl of AgNPs. Similarly, the haemolytic activity of V. alginolyticus showed a marked reduction from 24 h onwards at both AgNP exposure levels (50 μl and 100 μl). Bacterial sensitivity to AgNPs was found to vary among species, indicating pathogen-specific responses to AgNP treatment. Keywords: Antibacterial activity, Bacterial sensitivity, Minimum inhibitory concentration, Nanomaterials in aquaculture, Virulence factors

Review

This study presents a timely investigation into the antibacterial efficacy of green-synthesised silver nanoparticles (AgNPs) against a panel of major bacterial fish pathogens, with a commendable focus on their impact on bacterial virulence factors. The green synthesis approach, utilising starch and glucose, aligns well with sustainable practices and is complemented by a robust set of characterisation techniques including FTIR, TEM, DLS, and XRD, ensuring the physical and chemical properties of the synthesised AgNPs are well-defined. The evaluation against nine diverse fish pathogens, encompassing both Gram-positive and Gram-negative species, provides a broad assessment of the AgNPs' potential in aquaculture disease management. A significant strength of the work lies in moving beyond simple bactericidal activity, assessed via MIC and disc diffusion, to explore the AgNPs' influence on key virulence factors. The abstract specifically highlights the complete inhibition of starch hydrolysis in *Aeromonas hydrophila* and a marked reduction in haemolytic activity of *Vibrio alginolyticus* at specific AgNP exposure levels and time points. These findings are crucial as they suggest that AgNPs not only inhibit bacterial growth but can also mitigate the pathogenic potential of these organisms, offering a more comprehensive protective strategy. The observed variability in bacterial sensitivity underscores the need for pathogen-specific applications and further tailored research. While the abstract effectively outlines the study's scope and key findings, a more detailed summary of the antibacterial activity (e.g., a range of MIC values or a general trend of sensitivity across all nine pathogens) would enhance its impact. Furthermore, while two specific examples of virulence factor inhibition are given, it would be beneficial to know if similar effects were observed, or assessed, for other pathogens in the panel, or if these two represent the most pronounced findings. Given the emphasis on "nanomaterials in aquaculture," a brief mention of the potential broader implications for fish health, or even preliminary considerations regarding their environmental fate or non-target toxicity, would provide a more complete picture of their applicability.

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