Virulent shiga toxin-producing Escherichia coli (STEC) O157:H7 ST11 isolated from ground beef in Brazil.

In this study, a total of 248 ground beef samples were analyzed for the presence of Shiga toxin-producing Escherichia coli (STEC). Out of these samples, only one (0.4%) tested positive for STEC. Further analysis using PCR confirmed the presence of all tested genes associated with STEC, including stx1, stx2, eae, ehx, uid, rfbO157, and fliCH7 in this isolate. Interestingly, no STEC strains were detected in the remaining 100 beef cut samples or the 100 chicken cut samples, indicating the absence of detectable STEC contamination in those specific samples. The isolated strain exhibited significant cytotoxic activity in Vero cells, indicating its ability to produce cytotoxic Shiga toxins. To further investigate the strain, whole-genome sequencing (WGS) analyses were performed. The resistome analysis revealed the absence of acquired antimicrobial resistance genes, indicating a pan-susceptible phenotype. However, this strain presented chromosomal mutations in gyrA, gyrB, parC, parE, pmrA, pmrB, and folP. Plasmid analysis identified the presence of two plasmids, namely IncFIB(AP001918) and IncFII. The multi-locus sequence typing (MLST) identified the strain as belonging to sequence type (ST) 11, which is associated with E. coli O157:H7 strains. The virulome analysis confirmed the presence of several canonical virulence markers, including stx1, stx2, eae-g01-gamma, ehxA, stx1a-O157, and stx2a-O157. Overall, this study identified for the first time a rare occurrence of STEC contamination in ground beef, with the isolated strain belonging to the highly virulent O157:H7 serotype. These findings contribute to our understanding of STEC prevalence and characteristics in food samples, highlighting the importance of effective food safety measures to prevent potential health risks associated with STEC contamination.