<s>[INST] context: Under harsh environmental conditions, certain gram-positive bacteria convert from the vegetative state into a dormant state or spore. The spores, which are dehydrated structures, protect bacterial DNA and other contents from the effect of the intense heat, radiation, and standard disinfectants. If spores present in the food are not killed during preparation, and if the cooked food is left for several hours at room temperature, the spores will germinate allowing vegetative bacteria to produce the enterotoxin. The spore-forming gram-positive bacteria (a), Clostridium perfringens and Bacillus cereus, produce enterotoxins that cause watery diarrhea and abdominal cramps but no fever. While very similar, the vignette suggests C. perfringens as the etiologic agent. Onset is more rapid than with B. cereus diarrheal toxin, and while the types of food overlap, temperature-abused food is frequently associated with C. perfringens. Among the gram-positive cocci (b), Staphylococcus aureus produces enterotoxin, but the onset is more abrupt (1-6 hours) and fever may be present. The gram-negative bacilli (a) must first colonize the intestine and grow, even if an enterotoxin is at the root of the diarrhea. Thus, onset of symptoms occurs from 24 hours to several days after ingestion of the food. Opportunistic fungi (d) are not known to be involved in food poisoning. Enteric viruses (e) such as norovirus and rotavirus require 12 to 48 hours and 1 to 3 days, respectively, for symptoms to appear. They are more commonly associated with foods contaminated by food workers during preparation (salads, sandwiches, and fruit), or food prepared with contaminated water (salads, fruit, and ice). [/INST] question: Guests at a party consumed beef broth that was boiled earlier in the day but left at room temperature for several hours. The individuals presented with symptoms of food poisoning, including watery diarrhea and abdominal cramps, 8 to 10 hours later. The symptoms lasted 24 hours. The agent that caused the symptoms is most likely which of the following? | options: A: Spore-forming gram-positive bacilli B: Gram-positive cocci C: Gram-negative bacilli D: An opportunistic fungus | answer: A </s>