Use of Thermal and Emerging Non-Thermal Treatments Reveal Biomolecular and Morphological Changes in Pathogenic E. coli

(1) Background: We sought to explore the changes in the biomolecular profile and morphology of Pathogenic heat-resistant E. coli isolated from animal-based food. (2) Methods: Six strains underwent heat (60 °C for 6 min), ultrasound (US; 299 W), UVC (4950 mJ/cm²), and combined treatments (UVC+US and heat+UVC). Afterwards, biomolecular characterization across four spectral regions was evaluated by Fourier transform infrared (FT-IR) spectroscopy and analyzed by principal component analysis (PCA) for treated and non-treated strains (control group). These regions are fatty acids (3010–2800 cm⁻¹), proteins and peptides (1700–1200 cm⁻¹), carbohydrates (1200–900 cm⁻¹), and amide A (3280–3120 cm⁻¹). Additionally, treated and untreated strains were assessed for surface damage using scanning electron microscopy (SEM). (3) Results: Among all the regions studied, the amide A and fatty acids regions exhibited the most significant variations in absorbance for treated strains compared to the control. Treatments such as US, heat, and UVC+US tended to increase Principal Components (PCs) and, consequently, absorbance. On the other hand, UVC and heat+UVC showed the opposite trend in these regions. SEM images showed filamentous cells for strains treated with UVC and UVC+US, indicating that cells continued to replicate under these conditions. These results highlight how thermal and non-thermal treatments influence specific biomolecular and morphological regions of E. coli. The methodologies used provide reliable data for understanding stress responses, which can guide the development of more effective technologies for eliminating multi-resistant pathogens.