Isolation and Characterization Through Whole-Genome Sequencing of STEC Strains from Free-Ranging Red Deer

Whole-genome sequence (WGS) analysis was used in this study to characterize Shiga toxin-producing Escherichia coli (STEC) isolates in free-ranging red deer from the central Italian Alps. Fecal samples from 92 hunted red deer collected between September and December 2022 were analyzed for the presence of STEC. Single E. coli colonies positive by PCR for stx genes were analyzed by WGS. STEC were isolated from eleven (12%) samples, showing eight stx2b, one stx2a, two stx1c, and one stx1a subtypes. Different serotypes and sequence types were identified (n = 8 each). Three isolates of O27:H30 serotype and ST753 showed no correlation in the cgMLST analysis (AD range 44-98). All strains harbored additional virulence factors. The only isolate harboring stx2a also possessed the eae gene and belonged to serotype O26:H11. Some isolates displayed shuffled virulence features of more than one E. coli pathotype. The high genetic diversity of strains circulating in the red deer population living in the central Italian Alps, including the STEC O26:H11 strain associated with STEC from severe disease in humans, confirms red deer as STEC reservoirs and highlights the need for monitoring the presence of these pathogens in wild ruminants.