Can Extraintestinal Pathogenic Escherichia coli with Heat Resistance Profile Overcome Nonthermal Technologies?

Ultraviolet-C light-emitting diode (UVC-LED) and ultrasound (US) are two nonthermal technologies with the potential to destroy pathogens. However, little is known about their effectiveness in strains with a history of heat resistance. Thus, this study aimed to evaluate the phenotype and genotype of heat-resistant extraintestinal pathogenic Escherichia coli (ExPEC) with heat resistance genes after the application of US, UVC-LED, and UVC-LED+US. For this, two central composite rotatable designs were used to optimize the UVC-LED and US conditions in four ExPEC isolated from beef. From the genome of these isolates obtained in a previous study, possible genes for UVC resistance were analyzed. Results showed that US was ineffective in reducing >0.30 log colony-forming unit/mL, and that when used after UVC-LED, it showed a nonsynergic or antagonistic effect. Also, UVC-LED had the greatest effect at the maximum dose (4950 mJ/cm² from 1.65 mW/cm² for 50 min). However, the strains showed some recovery after that, which could be implicated in the expression of genes included in SOS system genes, some others present in the transmissible Locus of Stress Tolerance (trxBC and degP), and others (terC). Thus, ExPEC can overcome the conditions used in this study for US, UVC-LED, and UVC-LED+US, probably due to the history of resistance to other cellular damage. The result of this study will contribute to future studies that aim to find better treatment conditions for each food product.