# Optimization of probiotic-mediated selenium nanoparticles for superior antibacterial action against methicillin-resistant Staphylococcus aureus

## TL;DR

This study uses probiotics to create selenium nanoparticles that are more effective than linezolid in fighting MRSA, a drug-resistant bacteria.

## Contribution

A novel method for optimizing probiotic-mediated SeNP synthesis to enhance antibacterial activity against MRSA.

## Key findings

- Optimized SeNPs showed higher antibacterial activity than linezolid against MRSA.
- SeNPs had a uniform rod shape and a protein coat, contributing to stability and effectiveness.
- The MIC/MBC of SeNPs was 50 µg/ml, twice as potent as linezolid.

## Abstract

The need for new bactericidal agents is becoming increasingly crucial as current antibiotic treatments are becoming less effective against methicillin-resistant Staphylococcus aureus (MRSA). The present study involves the biosynthesis of selenium nanoparticles (SeNPs) using the cell-free supernatant of Limosilactobacillus fermentum (OR553490). To achieve the two objectives of optimizing the biosynthesis of SeNPs and enhancing their antibacterial activity, response surface methodology (RSM) coupled with the Box–Behnken design was employed to vary the components to achieve the desired outcomes. For the maximum production of biosynthesized SeNPs (ODmax), the optimum conditions were found to be a Na2SeO3 concentration of 30 mM at pH 7, incubation temperature within the 30–40 °C range for 72 h, and a metabolite-to-precursor ratio within the range of 1:1 to 1:4 (v/v%). Conversely, for maximum antibacterial activity against MRSA (strain ATCC 43300), the optimum conditions are a higher precursor concentration (50 mM) at a 1:1 ratio (30 °C for 48 h). The SeNPs were well characterized; most were coated with a protein layer and had a uniform rod-shaped structure with a mean diameter of 30.94–43.94 nm. The presence of the protein coat was confirmed by the presence and identification of an amine and C–N band in the FT-IR spectrum. The synthesized protein-coated SeNPs exhibited a zeta potential of − 20.93 ± 5 mV, which indicates good stability. Both optimized SeNPs and linezolid were tested against MRSA, with the SeNPs demonstrating greater anti-MRSA activity than linezolid, which served as the clinical benchmark. SeNPs demonstrated identical minimum inhibitory and bactericidal concentrations (MIC/MBC) of 50 µg/ml, effectively doubling the potency of linezolid (MIC/MBC: 100/110 µg/ml). Probiotic-mediated rod-shaped SeNPs may offer an environmentally viable solution for treating drug-resistant bacterial infections.