What is different about interaction of Salmonella with the immune system of the body?

Salmonella is a gram negative bacterium. Unlike other bacteria, Salmonella does not cause tissue damage in the body. In fact it releases a protein AvrA. This protein punches through the intestinal wall and reaches the cells. Here it secretly multiplies itself until its number reaches a threshold level. After reaching the threshold, the bacteria attack the body with full force leading to symptoms like nausea, diarrhea, vomiting etc.