Enterobacter spp. lactose negative findings and their implications on food safety

This study provides Enterobacter spp. lactose negative strains characterization susceptible of being wrongly identified as Salmonella spp. having into account its meaning for what concerns on food safety. More than five hundred feed samples for farm animal feeding were microbiologically analyzed according the Spanish Normative for feed, in which different media are accepted for detecting Salmonella spp. after performing preenrichement steps. In this study SS agar was chosen for differential isolation. Results show that 55% of those colonies supposed to be Salmonella spp. belonged to the genus Enterobacter when performing confirmation by means of API20E method and TSI/LIA tests, indicating that several strains of the genus Enterobacter have lost their condition of lactose positive microorganisms and becoming lactose negative, inducing confusion when trying to identify Salmonella spp. by traditional and reference methods.