What is the most likely causative agent of stomach cramps after eating ham at a restaurant?

The most likely causative agent of stomach cramps after eating ham at a restaurant is often associated with Salmonella. Salmonella is a bacterium commonly found in various food sources, including poultry, eggs, and sometimes meat like ham. It can lead to foodborne illness characterized by symptoms such as stomach cramps, diarrhea, and fever shortly after consuming contaminated food.

In the context of the question, Salmonella is a more common pathogen associated with meat products than the other listed options. While Campylobacter is primarily linked to poultry and E. coli is mostly associated with undercooked beef or contaminated produce, Listeria more often occurs in processed deli meats and unpasteurized dairy products.

Thus, when considering the typical sources of foodborne pathogens related to ham, Salmonella stands out as the principal risk, specifically in restaurant settings where food handling practices may impact safety. Hence, it's important to consider the context of the food consumed and its usual associations with certain pathogens when identifying potential causes of foodborne illness.