# Investigating Salmonella biofilm responses to antibiotic treatment using optical photothermal infrared spectroscopy

## TL;DR

This study uses a new imaging technique to track how Salmonella biofilms respond to antibiotics by analyzing their metabolism at different depths.

## Contribution

A novel method combining optical-photothermal infrared spectroscopy and 13C isotope probing is introduced to study biofilm metabolism.

## Key findings

- Metabolic gradients in biofilms show low activity in the core and higher activity in outer regions.
- Antibiotic exposure alters metabolic responses in Salmonella biofilms depending on bacterial resistance profiles.

## Abstract

Biofilms are microbial communities of aggregated cells encased in extracellular matrix that are a pressing healthcare concern. Since biofilms have complex metabolic dynamics, in this study a new approach for studying biofilm metabolism is developed that employs optical-photothermal infrared (O-PTIR) spectroscopy imaging combined with 13C stable isotope probing and cryosectioning to track the carbon metabolism of cells at different depths of the biofilm. This approach demonstrated that metabolic gradients can be visualised using O-PTIR imaging, revealing a core of cells with low metabolic activity at the centre of the biofilm, with outer regions showing significantly higher metabolic activity. By incorporating the heavy stable isotope of carbon into bacterial biomass, we monitored the metabolic activity of gentamicin-resistant Salmonella Typhimurium within the biofilm structure upon exposure to various antibiotics. O-PTIR imaging revealed altered metabolic responses at various depths of the biofilm, with variations that depend on the bacterial antibiotic susceptibility profile.

Optical-photothermal infrared spectroscopy imaging combined with 13C stable isotope probing reveals changing carbon metabolic gradients in Salmonella Typhimurium biofilms in response to antibiotic treatments.