[BjoernKW]

Yes, the salt mainly is meant to reduce irritation.

Amoeba aren't bacteria, though. Both, however should be adversely affected by saline solutions because osmosis will draw water out of the cells, effectively killing these organisms.

Salt can be as effective a disinfectant as chlorine if dissolved in water. There are public swimming pools that make use of this because chlorine can have adverse effects on your health, such as causing irritation on both the skin and the respiratory system.