The Genetic Legacy of Thermal Processing in Pasteurized Foods: Persistence of Antimicrobial Resistance Genes, Potential for Horizontal Gene Transfer, and a Proposed Genetic Legacy Index

Thermal processing inactivates foodborne bacteria but does not necessarily destroy their DNA, membrane vesicles, or bacteriophage particles. Such residues persist in pasteurized milk and heat-treated meat and are ingested by consumers. Whether this material can transfer antimicrobial resistance genes (ARGs) to gut bacteria remains untested: the only direct human evidence of foodborne resistance-gene transfer involved live bacteria, not material released from heat-killed cells. This narrative review synthesizes evidence on the post-thermal fate of extracellular DNA, membrane vesicles, and bacteriophages, grading that evidence explicitly from detection of a target sequence, through structural integrity, to demonstrated transfer under realistic conditions. Persistence of ARG sequences after pasteurization is well documented, whereas functional transfer from foodborne dead-cell material has not been demonstrated in vivo . A Genetic Legacy Index (GLI) is proposed as a conceptual measurement framework—not a validated index—combining extracellular DNA abundance, ARG load, and ARG–mobile genetic element linkage, with an illustrative formula, normalization strategy, and validation agenda. Current finished-product microbiological criteria are predominantly culture-based and do not establish limits for extracellular or dead-cell genetic material, although integrated antimicrobial resistance surveillance increasingly includes molecular detection and whole-genome sequencing. The GLI is therefore proposed as a research and surveillance tool rather than a product-release criterion: a first step toward evaluating an unquantified exposure pathway within One Health surveillance of the food chain.