If you have more than one positively charged atom of silver in a particle, then each can attract a negatively charged atom or particle. If a clump of silver atoms binds with two negatively charged particles, such as oxygen and something else, these two particles will no longer electrostatically repel each other, but will be brought together and will react, oxidizing the particle. The larger the particle, the more positively charged silver atoms can attract oxygen and other negatively charged particles to the surface. If particle size becomes too large, then the amount of silver hidden in the center of the particle means that the increase in mass, which goes up with the cube of the diameter, is increasing faster than the active surface areas, which goes up at the square of the diameter. The catalytic effect thus peaks at some particle size and decreases with respect to the amount of silver if the size is increased further.
Bacteria come in two forms - anaerobic and aerobic.
Earlier this century, it was discovered by Dr. Gram that he could stain bacteria with a specially prepared Gram stain, and that in general good bacteria stained, but pathogenic bacteria did not stain. It was later discovered that the pathogenic bacteria are negatively charged. Most pathogenic bacteria are anaerobic, and if oxidized will die. In order to prevent oxidization, they carry an enzyme to repel negatively charged oxygen. If this enzyme is disabled so that they lose this negative charge, or if oxygen is supplied in a form such that it is reactive to negatively charged pathogens, such as ozone water or hydrogen peroxide, the bacteria will be oxidized.