Using a variety of samples and methods, the researchers were able to differentiate which microorganisms were already present in the body during his lifetime and which only colonized it after his death—both during the time in the glacier and over three decades of preservation. In samples of internal tissue, the team was able to detect genetic material from bacteria belonging to Ötzi's original gut flora.

A surprising finding is the presence of cold-adapted yeast species, likely originating from the glacial environment, that have persisted on Ötzi's body to the present day. These cold-tolerant yeasts may also hold potential for industrial applications. The study appears in Microbiome.

It was an extensive investigation, in which the research team analyzed ice from the surface as well as meltwater from inside the mummy and collected numerous samples by swab. Data from intestinal tissue and stomach contents were available from previous studies. A soil sample from the discovery site, collected and frozen during Ötzi's recovery in 1991, was also analyzed to trace environmental influences.

Researchers also identified genetic material from the original gut microbiome in the intestinal tract and stomach content. This microbiome, first described in a 2019 study conducted by Eurac Research, closely resembles the few known examples of gut flora from early human populations—such bacteria are rarely found in the intestines of modern humans living in industrialized societies. Ötzi therefore offers a rare glimpse into humanity's microbial past.