Final answer:
E. coli O157:H7 is deadly due to its production of Shiga toxin, leading to severe health complications such as bloody diarrhea and hemolytic uremic syndrome (HUS).
Step-by-step explanation:
The strain Escherichia coli O157:H7 is considered deadly because it produces Shiga toxin, which can inhibit protein synthesis within host cells and lead to serious health complications such as bloody diarrhea and hemolytic uremic syndrome (HUS). This is in contrast with many other strains of E. coli that are non-pathogenic and do not produce such toxins. E. coli O157:H7 has caused numerous outbreaks through contaminated food and water, leading to recalls and significant health crises. The presence of Shiga toxin genes in this strain is a result of horizontal gene transfer, most likely through transduction from a bacteriophage that once infected Shigella dysenteriae. Its virulence is due to specific antigens on its surface, identified by the O and H in its name, which refer to surface structures and flagella, respectively, and contribute to the bacterium's ability to cause disease.