Assessing the risk of cross-tolerance to heat in Escherichia coli exposed to antibacterial Blue Light

Escherichia coli, includes pathogenic strains that contaminate food products, creating challenges for the food industry. Non-thermal methods like antimicrobial blue light (aBL) are gaining attention as an alternative to thermal processing. This study assessed whether cross-tolerance could develop between aBL and heat treatments in E. coli under sublethal stress conditions. Experiments were performed using E. coli and 64 aBL-hypersensitive mutants. aBL tolerance was developed through 10 days of sublethal exposure, while heat-tolerant strains were exposed to 52°C for 20 minutes. Cross-stress tolerance risk was then assessed. Repeated sublethal exposure to heat and aBL resulted in stable phenotypic adaptations. Populations with increased aBL tolerance showed enhanced heat tolerance. Genomic analysis identified 11 genes involved in cross-stress tolerance. These adaptations did not affect antibiotic susceptibility. aBL shows promise as a complementary food processing tool, though the risk of cross-tolerance should be considered when combining aBL with heat treatments.