# Lectin-Coated Silver/Silver Chloride Nanoparticles in Combination with Gentamicin: A Strategy to Preserve Antibiotic Efficacy at Lower Doses Against Pathogenic Planktonic Bacteria

## TL;DR

This study shows that combining gentamicin with lectin-coated silver nanoparticles can significantly reduce the antibiotic dose needed to fight planktonic bacteria.

## Contribution

A novel strategy using lectin-coated silver nanoparticles to enhance gentamicin efficacy at lower doses is proposed.

## Key findings

- The combination reduced gentamicin MIC by over 90% against Staphylococcus aureus and Pseudomonas aeruginosa.
- Fractional inhibitory concentration indexes confirmed synergistic antibacterial activity.
- The combination showed bactericidal effects but had limited impact on biofilm formation at higher concentrations.

## Abstract

The rampant overuse of antibiotics in recent decades
has significantly
contributed to the emergence of antibiotic resistance. This highlights
the need for new antibacterial strategies to reduce dependence on
traditional antibiotics and slow the development of resistance. Concanavalin
A-coated silver/silver chloride nanoparticles (ConA/Ag/AgCl-NPs) offer
a promising alternative, combining the antimicrobial activity of metallic
silver with the ability of concanavalin A to interact with both membrane
carbohydrates and antibiotic gentamicin. The aim of this study is
to investigate the synergistic antibacterial activity of gentamicin
combined with ConA/Ag/AgCl-NPs against pathogenic bacteria. Our results
confirmed that gentamicin interacts with ConA/Ag/AgCl-NPs, altering
their plasmonic resonance properties. The combination of gentamicin
with ConA/Ag/AgCl-NPs significantly reduced the minimum inhibitory
concentration (MIC) values of both, from 0.19 μg/mL and 0.04
μg/mL to 0.02 μg/mL and 0.01 μg/mL, respectively,
required to inhibit planktonic Staphylococcus aureus. Similarly, the MIC values required to inhibit planktonic Pseudomonas aeruginosa reduced from 0.39 μg/mL
and 0.02 μg/mL to 0.02 μg/mL and 0.0012 μg/mL, respectively.
In both cases, a reduction of more than 90% in the amount of gentamicin
used was observed. These data demonstrate synergistic antibacterial
activities, as revealed by the fractional inhibitory concentration
indexes below 0.5. Additionally, a killing kinetic assay confirmed
bactericidal effects of the combination against both strains tested.
Conversely, for both strains, ConA/Ag/AgCl-NPs exhibited substantial
reduction in biofilm formation only at a concentration at least 500-fold
greater than the MIC values observed for planktonic cells. Therefore,
the strategy presented here allows for significantly lower doses of
gentamicin to achieve the same level of effectiveness against pathogenic
planktonic bacteria.