The outermost layer of a bacteria cell is called a capsule. The capsule majorly consists of polysaccharides, and the nature of polysaccharides are they are not easily washed away with water. Thus, bacteria has its power to cause diseases and sickness.
The capsule plays a big role in causing diseases of a bacteria as it strongly protects the bacteria cells from being engulfed by eukaryotic cells. One maybe immune to one type of capsule but it does not mean that he or she is immune to all other types. That is why it is important to wash our hands with soap and water in order to avoid getting ill from disease-causing bacteria.