Which process is NOT caused by microorganisms in post-mortem changes?

Rigor mortis is a post-mortem change that is primarily caused by biochemical processes within the body, specifically the depletion of ATP (adenosine triphosphate) after death, leading to muscle stiffening. This process occurs within hours of death and is driven by physiological changes rather than microbial action.

In contrast, mortis encompasses the types of changes that occur after death, including rigor mortis, livor mortis, and algor mortis, all of which can occur without the involvement of microorganisms. Decomposition and fermentation, on the other hand, are processes that are significantly influenced by the activity of microorganisms.

Decomposition involves the breakdown of bodily tissues facilitated by bacteria, fungi, and other microorganisms that thrive in the anaerobic environment of a corpse. Fermentation, which can also be caused by microorganisms, occurs when organic matter is broken down into simpler compounds, producing byproducts that affect the body's chemistry after death. This highlights that both decomposition and fermentation are directly associated with microbial activity, while rigor mortis is an automatic physical response due to chemical changes in the body.