Is there any risk of illness from eating a bunch of fresh grapes?

Depending on how they are grown, harvested, and processed, fresh grapes may harbor pathogenic bacteria such as E. coli and salmonella. The human hand can pass these bacteria from bunch to bunch or grape to grape at several junctures in the food chain. Contamination also can occur at the supermarket or in the home. Before grapes are harvested, water can cause contamination, as can birds and other wildlife.
 
Bacteria can also multiply on grapes as a result of improper storage or proper storage over an extended period of time. They are also subject to mold growth, particularly in moist environments.  Fortunately, proper storage and handling  of fresh grapes eliminate most risk of illness.
 
Source(s):
FDA "Guide to Minimize Microbial Food Safety Hazards for Fresh Fruits and Vegetables"