Final answer:
E. coli O157:H7 is deadly due to the production of Shiga toxin, a heat-labile exotoxin that can cause severe health complications like bloody diarrhea and kidney failure. Unlike endotoxins which are heat-stable, Shiga toxin is denatured at higher temperatures, underlining the heat-labile nature of many exotoxins.
Step-by-step explanation:
The reason why E. coli O157:H7 is deadly compared to other non-pathogenic strains, referred to as HS in the question, is mainly due to the production of a particular toxin known as Shiga toxin. E. coli O157:H7 is a type of enterohemorrhagic E. coli (EHEC) that produces Shiga toxin, which can cause severe damage to the host including bloody diarrhea, inflammation, and potential renal failure. It's this Shiga toxin, originally from Shigella dysenteriae, that gives EHEC its pathogenicity, allowing it to also cause outbreaks that can lead to serious health complications like hemolytic uremic syndrome (HUS).
Moreover, the majority of exotoxins, including Shiga toxin, are heat-labile, meaning they are inactivated at higher temperatures. This differs from endotoxins which are heat-stable and require much higher temperatures to denature. Given the context of the question, none of the options exactly describe why O157:H7 is deadly, but the closest one referencing toxin production would be option A) O157:H7 produces a heat-labile toxin, while HS would presumably not produce this toxin or would produce a different, less virulent exotoxin.