FMGE 2013 — Microbiology

Question 1: Symptoms of food poisoning seen within 6 h are commonly due to:

• A. Shigella
• B. Bacillus cereus
• C. Staphylococcus aureus (Correct Answer)
• D. Salmonella

Explanation: ***Staphylococcus aureus*** - Food poisoning due to *Staphylococcus aureus* is caused by preformed **enterotoxins** in the food, leading to rapid onset of symptoms, typically within 1-6 hours. - Common symptoms include **nausea**, **vomiting**, **abdominal cramps**, and **diarrhea**, often appearing abruptly and resolving within 24-48 hours. *Shigella* - *Shigella* infections typically cause symptoms after an **incubation period of 1-7 days**, which is much longer than the 6-hour window. - It is characterized by **dysentery** (bloody and mucoid stools), fever, and severe abdominal cramps, resulting from direct invasion of the intestinal mucosa. *Bacillus cereus* - *Bacillus cereus* can cause two types of food poisoning: diarrheal (onset 6-15 hours) and emetic (onset 0.5-6 hours). While the emetic form can occur within 6 hours, it is more specifically associated with contaminated **rice products** and prominent vomiting. - The emetic type is due to a **preformed toxin (cereulide)**, but *S. aureus* is a more common and general cause of rapid-onset food poisoning across various food types. *Salmonella* - Food poisoning from *Salmonella* typically has an **incubation period of 6 hours to 6 days**, usually 12-72 hours. - Symptoms include **fever**, diarrhea (which can be bloody), abdominal pain, nausea, and vomiting, and are due to bacterial invasion rather than preformed toxin.