Aims: The production of putrescine is a relevant property related to food quality and safety. Morganella morganii is responsible for putrescine production in fresh fish decomposition. The aim of this study was to gain deeper insights into the genetic determinants for putrescine production in M. morganii. Methods and Results: The 6972 bp DNA region showed the presence of three complete and two partial open reading frames all transcribed in the same direction. The second and third genes putatively coded for an ornithine decarboxylase (Spel') and a putrescine-ornithirle antiporter (PotE), respectively, and constituted an operon. The speF gene has been expressed in Escherichia coli HT414, an ornithine clecarboxylase defective mutant, resulting in ornithine clecarboxylase activity. The genetic organization of the SpeF-PotE- encoding region in M. morganii is different to that of E. coli and several Salmonella species. Conclusions: The speF gene cloned from M. morgami encodes a functional ornithine decarboxylase involved in putrescine production. Phylogenetic tree based on 16S rDNA showed that ornithine decarboxylase activity is not related to a specific phylogenetic tree branch in Enterobacteriaceae. Significance and Impact of the Study: The identification of the DNA region involved in putrescine production in M. morganii will allow additional research on their induction and regulation in order to minimize putrescine production in foods.