A large number of patrons of a restaurant in a large city develop symptoms of food poisoning. Officials collect several foods that are suspected in the episode. Which of the Gram-positive bacteria in this chapter may be responsible for the food poisoning? How do health officials determine which bacterium is the culprit?

Question

What will be an ideal response?

Answer 1

Possible causative agents include Staphylococcus aureus, Clostridium perfringens, and Listeria monocytogenes. The symptoms are different with the different bacteria. S. aureus food poisoning starts about 4 hours with nausea, diarrhea, severe cramping and vomiting, and lasts about 24 hours. C. perfringens food poisoning is less severe with cramping and watery diarrhea but no nausea, vomiting or fever, and lasts less than 24 hours. Listeria monocytogenes causes mild symptoms of sore throat and low grade fever with little to no intestinal distress. However, it is the most serious of the three because it is an infection, not an intoxication (and technically not food poisoning in the most literal sense). Listeriosis can lead to far more serious disease in pregnant women and people with reduced immune function.
Bacteria are not always detected in contaminated food, but if present can be distinguished by Gram staining. S. aureus are cocci in irregular clusters C. perfringens are large nearly rectangular bacilli (endospores may be present) and are usually present in large numbers in cases of food poisoning. L. monocytogenes are smaller bacilli with no endospores, and can be recovered by cold enrichment culturing.