A cook prepares sandwitches for 10 people going for picnic. Eight out of them develop severe gastroenteritis within 4-6 hrs of consumption of the sandwitches. It is likely that on investigation, the cook is found to be carrier of:
Staphylococcal food poisoning is caused by enterotoxin. The enterotoxin is a preformed toxin, already present in the contaminated food before consumption.
Milk and milk products and animal products like fish and meat kept at room temperature after cooking are mainly incriminated.
When kept at room temperature, the contaminating staphylococci multiply and produce toxin adequate enough (as little as 25g of toxin B can lead to illness) to cause food poisoning.
Often a food handler, who either is a carrier of S. aureus (nose, skin) or is suffering from staphylococcal skin infection, is the source of infection. 
The onset of symptoms is sudden, appearing within 2–6 hours of ingestion of food. It is a self-limiting condition characterized by nausea, vomiting, abdominal cramps, and watery, non-bloody diarrhea.

Parija SC. Textbook of Microbiology & Immunology. Elsevier Health Sciences; 2014. Page: 178
Salmonella typhi
Vibrio cholerae
Entamoeba histolytica
Staphylococcus aureus