Colloidal Silver is the worlds oldest known natural antibiotic.
It is very very simply tiny particles of silver suspended in water.
A colloid is a solution that has particles ranging between 1 and 1000 nanometres in diameter, yet are still able to remain evenly distributed throughout the solution. These are also known as colloidal dispersions because the substances remain dispersed and do not settle to the bottom of the container. (Wiki)
The silver colloids disable an aerobic bacteria’s ability to produce oxygen to feed itself by inhibiting the production of the enzyme that the bacteria uses to produce the oxygen. This you tube video by 1beinki explains the process beautifully.