Ethanol and Higher Alcohols’ Production in Fungal and Bacterial Laboratory Cultures and Significance for Forensic Samples

Abstract

Ethanol can be produced by many microorganisms that colonize a dead body. Ethanol’s concentration depends on the congener higher alcohols, 1-propanol, isobutanol, 2-methyl-1-butanol, 3-methyl-1-butanol, and 1-butanol, as previous research has shown. This correlation is expressed by mathematical models which estimate the concentration of microbial ethanol. The aim of this contribution was to study the ethanol and higher alcohols’ production in various laboratory bacterial and fungal cultures and the applicability of the bacterial and fungal models (which concern the bacteria E. coli, S. aureus, K. pneumoniae, and E. faecalis, and the fungus C. albicans) in these samples, as well as in blood samples from autopsy cases, with the overall objective of investigating the models’ applicability in routine casework. The bacteria and fungus were cultured in conventional culture media and in denatured human blood cultures under various conditions. The alcohols’ concentrations were determined using a head space–gas chromatography–flame ionization detector (HS-GC-FID). The previously reported bacterial and yeast models were applied in the cultured samples and in blood from 122 autopsy cases. Our results showed that 1-propanol was not produced by C. albicans and E. faecalis under certain conditions. Also, 1-butanol was not produced by C. albicans, E. faecalis, and K. pneumonia under certain conditions. Furthermore, the bacterial models were applicable in postmortem samples irrespective of the microbes that were possibly activated in the sample, while the EC models showed the best applicability among all the bacterial and yeast models. The best applicability of the bacterial models was observed in autopsy blood with 0.10 g/L < BAC < 1.0 g/L in cases of violent and undetermined causes of death and in cases with putrefaction. Finally, the yeast models were applicable in limited, possibly special, autopsy cases. In conclusion, it could be inferred that the source of ethanol in any given postmortem blood sample is likely microbial if either most bacterial models or at least one model from each distinct bacterial species is successfully applicable.