Misconception: All bacteria can be killed by colloidal silver.

At the moment, not every bacteria has been studied, and new strains come into existence every day. What can be said is that colloidal silver has proven effective against a very wide range of common bacteria.

Most pathogenic bacteria, especially bacteria with cell walls are rapidly destroyed. It is believed that the mechanism somehow involves blocking of essential enzymes by covalent binding of silver to the sulfur or amino groups. 

Resistance to silver, while possible, is very difficult and requires many mutations within the cells. Many bacteria have not been able to survive in the presence of silver for long periods of time. Some bacteria, especially the bacteria of intestinal flora, however, can survive and even manufacture silver nanoparticles out of an ionic environment; these bacteria are generally resistant to silver toxicity, as they have developed a mechanism to cope and safely deal with silver ions.

As described above, surprisingly (or maybe not) bacteria that can cope well and even manufacture silver nanoparticles are the same as those found in the lower digestive tract. Some of these beneficial bacteria and fungi are: Aspergillus fumigatus, Penicillium[ajc1]  species, Bacillus sp., Brevibacterium casei, Corynebacterium, L. fermentum, Enterococcus faecium, Lactococcus, Lactobacillus, Streptomyces hygroscopicus, E. coli, A. niger, and Enterobacter.

The bacterial development of silver resistance consists mainly of two mechanisms: the accumulation and storage of silver (generally redox chemistry); and the active efflux pump, which sends the silver ions out of the cell.

So yes most pathogenic bacteria and viruses are killed by silver, while most beneficial bacteria are preserved. This property alone makes colloidal silver superior to antibiotics.

“This statement has not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.”