Microbial Proteolytic and Hydrolytic Enzyme Kinetics in Postmortem Liquefaction and Tissue Degradation: A Systematic Review for PMI Mapping

Abstract

Background: Estimating the postmortem interval (PMI) beyond the early algor-mortis window remains one of the least standardized areas of forensic pathology. As decomposition proceeds, host autolytic enzymes and a succession of microbial proteases, lipases, and other hydrolases drive the progressive liquefaction of soft tissue, and the kinetics of this enzymatic activity have been proposed as quantitative PMI markers.

Objective: This systematic review synthesizes evidence on microbial proteolytic and hydrolytic enzyme activity during postmortem tissue liquefaction and degradation, and evaluates its utility, alongside host-derived enzymatic and omics markers, for PMI mapping.

Methods: A structured search of PubMed-, Scopus-, Web of Science-, and Google Scholar-indexed literature was conducted for studies published between July 2000 and April 2026 addressing protein, lipid, or other macromolecule degradation kinetics in postmortem tissue, with emphasis on microbial enzymatic drivers. Eligible study types included animal and human cadaveric studies, proteomic/metabolomic PMI studies, and systematic reviews; entomological and pure skeletal-isotope PMI methods without an enzymatic/biochemical component were excluded.

Key findings: Twenty-eight studies met inclusion criteria. Host calpain-mediated proteolysis dominates the first hours to days postmortem in skeletal muscle, while microbial hydrolasesgenerated as gut and environmental bacteria proliferate and disseminatebecome the principal driver of tissue liquefaction from roughly the second day onward, producing characteristic byproducts such as hydrogen sulfide, ammonia, and biogenic amines. Multi-omics and machine-learning approaches integrating these markers now predict PMI to within approximately one to two days across a multi-week range, substantially outperforming classical methods beyond the first 72 hours.

Conclusion: Microbial enzyme kinetics offer a biologically grounded, decomposition-resistant complement to host-protein degradation and entomological methods for PMI mapping, but standardization of sampling, enzyme assay, and statistical modelling is required before broad forensic validation. Practical and research implications are discussed.