Silver may be common in some places, but IIRC it isn't common inside animals or plants. So if you are a bacteria producing an infection, you would not expect to find a lot of silver inside your target. The metabolically paths that have resistance are usually more expensive, so the cheap path is usually selected and the other unused path is lost after some generations lost dew to random mutations.
It's possible that there exist some strange bacteria that feed on sulfur components and live inside mines with high silver concentration that have special mechanism to handle silver, but I think they are not very happy eating meat.