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 <i>Escherichia coli</i> (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 <i>E. coli</i> colonies positive by PCR for <i>stx</i> genes were analyzed by WGS. STEC were isolated from eleven (12%) samples, showing eight <i>stx2b</i>, one <i>stx2a</i>, two <i>stx1c</i>, and one <i>stx1a</i> subtypes. Different serotypes and sequence types were identified (<i>n</i> = 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 <i>stx2a</i> also possessed the <i>eae</i> gene and belonged to serotype O26:H11. Some isolates displayed shuffled virulence features of more than one <i>E. coli</i> 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.