# Femtosecond laser irradiation has an anti-virulence effect by reducing the adhesion and invasion of MRSA bacteria to human cells: an in vitro study

## TL;DR

A femtosecond laser treatment significantly reduces the ability of MRSA bacteria to stick to and invade human cells, offering a potential new approach to combat antibiotic-resistant infections.

## Contribution

The study demonstrates that sublethal femtosecond laser doses can impair MRSA virulence by reducing bacterial adhesion and invasion in human epithelial cells.

## Key findings

- A 50 mW, 15-minute femtosecond laser treatment reduced MRSA adhesion by 84–96% and invasion by 84–98%.
- Femtosecond laser exposure at higher durations (30 and 45 minutes) significantly reduced MRSA viability.
- All tested laser doses effectively impaired MRSA's ability to adhere to and invade epithelial cells.

## Abstract

Multidrug-resistant bacterial infections are a substantial global health challenge. Targeting bacterial virulence factors that control the progression, severity, and pathogenicity of bacterial infections could prevent and combat infection by intractable, potentially life-threatening pathogens such as methicillin-resistant Staphylococcus aureus (MRSA). Laser-based antibacterial photodynamic therapy (aPDT) has emerged as a promising alternative for infection management.

This study assessed the attenuation of adhesion and invasion of MRSA bacteria in two human epithelial cell lines, melanoma cells (A375) and breast ductal carcinoma (T47D), after exposure to different sublethal femtosecond laser doses. The INSPIRE HF100 laser system (Spectra Physics), pumped by a mode-locked femtosecond Ti: sapphire laser MAI TAI HP (Spectra Physics), was used to provide the femtosecond laser pulses at a wavelength of 400 nm for different durations; 15, 30, and 45 min., as well as different average powers; 50, 100, and 150 mW.

Our results showed that, an average power of 50 mW for 15 min. significantly reduced MRSA adhesion (by ~ 84–96%) and invasion (by ~ 84–98%), even though exposure durations of 30 and 45-min. resulted in reduced viability (p < 0.0001 by ANOVA and Tukey test).

All proposed femtosecond laser doses effectively impaired MRSA’s ability to adhere to and invade epithelial cells.

This diagram illustrates the experimental workflow for identifying the optimal femtosecond laser parameters to attenuate MRSA’s adhesion to and invasion of different epithelial cell lines. Following exposure to femtosecond laser irradiation, MRSA was co-cultured with epithelial cells for various infection durations. Adhesion and Invasion assays were done, and the adherent and invasive MRSA were quantified by colony-forming unit (CFU) counting, allowing for recommending an optimal femtosecond laser treatment for mitigating bacterial adhesion and invasion.